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cond-mat0511225

i

in recent years substantial efforts have been invested in miniaturizing chemical processes by building microfluidic systems . the `` lab on a chip '' concept integrates a great variety of chemical and physical processes into a single device @xcite in a similar way as an integrated circuit incorporates many electronic devices into a single chip . these microfluidic devices do not only allow for cheap mass production but they can operate with much smaller quantities of reactants and reaction products than standard laboratory equipments . even though most available microfluidic devices today have micron sized channels , further miniaturization is leading towards the nano - scale . there are two main lines of development for microfluidic systems . the first one encompasses systems with closed channels , essentially microfabricated tubes . however , closed channel systems have the disadvantage that they can be easily clogged by solute particles such as colloids or large bio - polymers . the second type consists of systems which are open with a free liquid - vapor interface , where the fluid is confined laterally not by geometrical but by chemical walls . the idea is that the liquid will be guided by lyophilic stripes on an otherwise lyophobic substrate @xcite . the substrate surfaces can be structured chemically by printing or photographic techniques . all these techniques are confined to two dimensions . while liquid flow in closed channel systems can be pumped by applying a pressure difference between the inlet and the outlet , the liquid - vapor interface of an open system would yield to the pressure ( like a very soft rubber tube ) and droplets would form . furthermore , upon pumping flow directions in interconnected open channel systems would be difficult to predict because small droplets may or may not inflate into larger ones , depending on details of the channel geometry and the filling state . however , there are a number of alternative ways to drive a liquid through a chemical channel . the most obvious one is to use inertia to drive the flow , e.g. , centrifugal forces or gravity , as occurs when a liquid film flows down an inclined plane . for films with thicknesses in the nanometer range one needs stronger accelerations in order to achieve a decent throughput . these can be realized most conveniently on a rotating disc ( e.g. , a spin coater or a centrifuge ) . electric forces are also commonly used in order to drive flows in small channels , e.g. , by using the electro - osmotic effect which , however , only works for liquids containing ions . since water is the most interesting liquid for biological applications , this is not a serious restriction . depending on the wall potential , a charged layer a few in thickness forms and an electric field applied parallel to the substrate will set the liquid in this layer in motion . while the electro - osmotic effect drives the liquid molecules at the substrate , the marangoni effect drives the molecules at the liquid - vapor interface . the origin of the marangoni forces are gradients in surface tension which arise from temperature gradients or from gradients in surfactant concentrations . the fourth method to cause flow in a chemical channel is wicking , i.e. , the sucking of a droplet into a chemical channel by capillary forces . here we consider inertial driving of the liquid , which is one of the most promising methods to generate flow in open microfluidic devices . marangoni forces could be induced easily by local heating of the liquid , but for volatile fluids like water this will lead to enhanced and undesirable evaporation . wicking is slow for longer channels and ceases to act as a driving force once the channel is filled . in principle , electrical forcing has the advantage that the direction of the force can be controlled on very small scales , but the required fields are high and might lead to electrolysis . in contrast , inertial driving can be realized easily by centrifugal forces and does not affect the liquid sample . our focus in this paper is the stability and robustness of one - dimensional channel flow ( i.e. , flow in a straight channel ) with inertial forcing aligned with the channel direction . the flow geometry is sketched in fig . [ fig : wurst ] . in the absence of forcing , a chemical channel filled homogeneously by a non - volatile liquid of fixed volume is unstable with respect to droplet formation when the contact angle with the triple - line pinned at the channel edge exceeds 90@xmath0 @xcite . this pearling instability is surface tension driven and similar to the rayleigh - plateau instability . the resulting drop shapes have been studied extensively in ref.@xcite . of particular interest is the question of spilling onto the lyophobic substrate , which can lead to cross - talk between neighboring channels . in the force - free case this happens for large droplets on chemical stripes on a partially wetting embedding substrate . in sec . [ sec : md ] we describe the formulation of the molecular dynamics ( md ) simulations for flow on a chemical channel and discuss the special case of unidirectional flow quantitatively . in sec . [ sec : pearl ] we discuss the appearance of pearling instabilities in channel flows and , in particular , we study the influence of the liquid ridge height ( effectively , the channel depth ) and of the wetting properties of the surrounding substrate on the stability of the liquid ridge . the full linear stability analysis of a stokes flow in sec . [ sec : stab ] as well as the hydrodynamic long - wavelength approximation developed in sec . [ sec : lw ] are in qualitative agreement with the md simulations . we discuss the results in sec . [ sec : disc ] . a liquid ridge on a chemical wetting stripe of width @xmath1 embedded in a solid substrate , which is non - wetting . gravity or inertial forces act on the liquid in the direction parallel to the @xmath2-axis . the liquid - vapor interface is parameterized in cylindrical coordinates as @xmath3 , and the local height @xmath4 . ]

we investigate the flow of a nano - scale incompressible ridge of low - volatility liquid along a `` chemical channel '' : a long , straight , and completely wetting stripe embedded in a planar substrate , and sandwiched between two extended less wetting solid regions . pearling instability develops if the thickness of the ridge exceeds half of the width of the channel . in the flowing case

we investigate the flow of a nano - scale incompressible ridge of low - volatility liquid along a `` chemical channel '' : a long , straight , and completely wetting stripe embedded in a planar substrate , and sandwiched between two extended less wetting solid regions . molecular dynamics simulations , a simple long - wavelength approximation , and a full stability analysis based on the stokes equations are used , and give qualitatively consistent results . while thin liquid ridges are stable both statically and during flow , a ( linear ) pearling instability develops if the thickness of the ridge exceeds half of the width of the channel . in the flowing case periodic bulges propagate along the channel and subsequently merge due to nonlinear effects . however , the ridge does not break up even when the flow is unstable , and the qualitative behavior is unchanged even when the fluid can spill over onto a partially wetting exterior solid region .

astro-ph0607095

i

advances in submillimeter continuum imaging techniques in the past decade have dramatically improved our understanding of the structure of the dense , cold interstellar medium ( ism ) in star - forming regions . in every region studied , the cold , dusty ism exhibits a clumpy , often filamentary structure whose density maxima correspond to sites of present or future star formation activity . the primary metric used to describe this inhomogeneous structure is the clump / core pc ) , dense condensations thought to be the immediate precursors of individual stars or small multiple systems . we use the term `` clump '' more generally to denote discrete structures which may form zero , one , or many stars and may therefore be much more massive than cores . in this sense , cores may be considered a subset of clumps . ] mass function . submillimeter continuum observations of the core mass function in nearby regions of low - mass star formation , such as serpens @xcite , @xmath3 oph @xcite , and orion b @xcite , have provided compelling evidence that the mass function of cold , dense cores mirrors the stellar initial mass function ( imf , e.g. @xcite , @xcite ) . it appears , therefore , that these dusty cores are the immediate precursors of stars . two main arguments are typically advanced in favor of this interpretation . first , both the stellar and core mass functions are well fit by salpeter - like power laws @xcite above @xmath41 @xmath5 . second , both the core and stellar mass functions appear to flatten out below @xmath41 @xmath5 and peak at about 0.1 @xmath5 @xcite . in other words , the core mass function and the stellar imf have similar _ shapes _ and intrinsic mass _ scales_. thus , by applying a more or less constant core - to - star mass conversion efficiency , the core mass function can be converted into the stellar imf . in papers i and ii in this series , we showed that , despite the large difference in the median clump mass , the clump mass function in massive star - forming regions ngc 7538 and m17 has a similar shape to that in low - mass star - forming regions ( @xcite ; papers i and ii hereafter ) . in both ngc 7538 and m17 , we found that double power law fits to the clump mass functions produce exponents which are consistent with the salpeter mass function @xcite . the similarities in their shapes suggests that the clump mass functions in low- and high - mass star - forming regions may have similar origins . what if the mass function of massive clumps were found to resemble that of massive stars , as is the case for low - mass stars ? that would suggest that massive clumps could also be converted to massive stars ( or small multiple systems ) on a more or less one - to - one basis . such a finding would lend weight to theories which suggest that massive stars form by the collapse of individual clumps @xcite , rather than those which suggest that massive stars form by coalescence or competitive accretion @xcite . to address these important matters , it is necessary to be able to accurately fit and interpret clump mass functions . in paper i , we argued that variations in analytic technique might account for much of the observed variation in the power - law exponents derived from fits to submillimeter continuum clump mass functions . in particular , we suggested that the systematic differences between the power - law exponents of clump mass functions in low- and high - mass regions probably result from the fact that the former are typically fit with two power law segments , while the latter are usually fit with only one ( compare @xcite and @xcite with @xcite and @xcite ) . in this paper , we extend and develop these arguments using a more thorough study of the available data on the submillimeter continuum clump mass function . in [ sec : howtofit ] , we discuss how best to fit a clump / core mass function , paying special attention to means by which the fits may be misinterpreted . in [ sec : funcform ] , we apply a consistent fitting methodology to determine which of several plausible functions best represents the clump / core mass function in a variety of star - forming regions . finally , in [ sec : compare ] , we use non - parametric tests to determine whether the shape of the clump / core mass function varies significantly from region to region or changes with the mass scale studied .

we investigate the mass function of cold , dusty clumps in 11 low- and high - mass star - forming regions . using a homogeneous fitting technique we find that the submillimeter continuum clump mass function in low - mass star - forming regions is typically best fit by a lognormal distribution , while that in high - mass star - forming regions is better fit by a double power law . we find no region - to - region trend in with the mass scale of the clumps in a given region , as characterized by their median mass . similarly , non non - parametric tests show that the _ shape _ of the clump mass function does not change much from region to region , despite the obvious changes in the intrinsic mass scale .

we investigate the mass function of cold , dusty clumps in 11 low- and high - mass star - forming regions . using a homogeneous fitting technique , we analyze the shape of each region s clump mass function and examine the commonalities among them . we find that the submillimeter continuum clump mass function in low - mass star - forming regions is typically best fit by a lognormal distribution , while that in high - mass star - forming regions is better fit by a double power law . a single power law clump mass distribution is ruled out in all cases . fitting all of the regions with a double power law , we find the mean power law exponent at the high - mass end of each mass function is , consistent with the salpeter result of . we find no region - to - region trend in with the mass scale of the clumps in a given region , as characterized by their median mass . similarly , non non - parametric tests show that the _ shape _ of the clump mass function does not change much from region to region , despite the obvious changes in the intrinsic mass scale . this result is consistent with the hypothesis that the clump mass distribution is determined by a highly stochastic process , such as turbulent fragmentation . it may also suggest that the data reduction and analysis techniques strongly affect the shape of the derived mass function .

astro-ph0607095

i

in this paper , we have examined the issue of the functional form of the clump / core mass function derived from millimeter / submillimeter continuum observations of galactic star - forming regions . we have demonstrated that , even in the case of a strict single power - law mass function , great care must be taken in fitting the cumulative form of the mass function to accurately measure the exponent of this power law . unexpected curvature can be introduced into the cmf when the range of masses or the number of objects is small , particularly when the power law is shallow ( @xmath22 with @xmath90 ) . in some cases , an intrinsically single power - law mass function might appear better fit by two or more power laws . in practice , the mass function is unlikely to be a pure single power law , so the potential to be mislead when fitting the cumulative mass function is even greater . we have fit 11 independent measurements of the clump / core mass function extracted from millimeter and submillimeter continuum observations of 7 star - forming regions . the masses of the clumps / cores in these regions collectively span more than five orders of magnitude . we find that , in regions where the median clump / core mass is less than a few @xmath5 , the clump / core mass function is best fit by a lognormal distribution . in more massive regions , a double power law provides a better fit to the clump cmf . at intermediate masses , both the lognormal and the double power law adequately describe the cmf . this difference in the functional form of the clump mass function may represent an evolution toward a lognormal mass function at lower masses and smaller spatial scales . this interpretation is consistent with theoretical explanations for the origin of a lognormal mass function via stochastic processes such as turbulent fragmentation and gravitational n - body interactions . the shape of the clump / core mass function does not appear to be a strong function of the intrinsic mass scale . the transition from lognormal to double power - law mass functions is fairly subtle . the mean value of the power - law exponent of the high - mass end of the clump / core mass function is found to be @xmath76 , consistent with the salpeter mass function . this result suggests that the shape of the stellar imf may be apparent in the clump mass function on clump mass scales of several tens of @xmath5 or more and linear scales of several tenths of a parsec . it also suggests that molecular cloud cores may be converted into stars ( or small multiple systems ) on an essentially one - to - one basis . this scenario is consistent with theories in which massive stars form by core collapse and disk accretion . it also relaxes the need to invoke either coalescence or competitive accretion to explain the formation of massive stars , though these processes probably do occur at some level . this result deserves further investigation , especially to constrain any instrumental or post - processing effects which may affect it . the similarities among the shapes of the various clump / core mass functions are confirmed to be statistically significant using non - parametric pair - wise comparisons of the cmfs . in 44 of 55 comparisons , after normalizing away the differences in their median masses , the clump / core mass functions are found to have a high likelihood of representing random samplings from the same parent distribution . that the observational cmfs agree well with the cmf of clumps extracted from a simulation of self - gravitating turbulent gas suggests that turbulent fragmentation is one possible sufficient explanation for the shape of the clump / core mass function . m. a. r. has been supported by an ontario graduate scholarship in science and technology . both m. a. r. and c. d. w. are supported by the natural sciences and engineering research council of canada ( nserc ) . m. a. r. would like to thank e. feigelson and f. motte for helpful discussions during the preparation of this manuscript . adams , f. c. , & fatuzzo , m. 1996 , , 464 , 256 bonnell , i. a. , bate , m. r. , clarke , c. j. , & pringle , j. e. 1997 , , 285 , 201 bonnell , i. a. , clarke , c. j. , bate , m. r. , & pringle , j. e. 2001 , , 324 , 573 bonnell , i. a. , larson , r. b. , & zinnecker , h. 2006 , preprint(astro - ph/0603447 ) bonnell , i. a. , vine , s. g. , & bate , m. r. 2004 , , 349 , 735 chabrier , g. 2003 , , 115 , 763 clark , p. c. & bonnell , i. a. preprint ( astro - ph/0603578 ) elmegreen , b. g. 2004 , , 354 , 367 gammie , c. f. , lin , y. , stone , j. m. , & ostriker , e. c. 2003 , , 592 , 203 israel , f. p. 1977 , , 59 , 27 johnstone , d. j. , wilson , c. d. , moriarty - schieven , g. , joncas , g. , smith , g. , gregersen , e. , & fich , m. 2000 , , 545 , 327 johnstone , d. j. , fich , m. , mitchell , g. f. , moriarty - schieven , g. 2001 , , 559 , 307 klessen , r. s. , burkert , a. , & bate . m. r. 1998 , , 501 , l205 klessen , r. s. 2001 , , 556 , 837 klessen , r. , & burkert , a. 2000 , , 128 , 287 kramer , c. , stutzki , j. , rhrig , r. , & corneliussen , u. 1998 , , 329 , 249 kroupa , p. 2002 , science , 295 , 82 krumholz , m. r. , mckee , c. f. , & klein , r. i. 2005 , , 618 , 33 krumholz , m. r. 2006 , , 641 , l45 larson , r .b . 1973 , , 161 , 133 maz - apellniz , j. & beda l. 2005 , preprint ( astro - ph/0505012 ) mckee , c. f. , & tan , j. c. 2002 , , 416 , 6876 mckee , c. f. , & tan , j. c. 2003 , , 585 , 2 mookerjea , b. , kramer , c. , nielbock , m. , & nyman , l .- . 2004 , , 426 , 119 motte , f. , andr , p. , ward - thompson , d. , bontemps , s. 2001 , , 372 , l41 motte , f. , andr , p. , & neri , r. 1998 , , 336 , 150 motte , f. , schilke , p. , & lis , d.c . 2003 , , 582 , 277 padoan , p. & nordlund , . 2002 , , 576 , 870 press , w. h. , teukolsky , s. a. , vetterling , w. t. , & flannery , b. p. 1992 , numerical recipes in fortran , ( 2nd ed . , cambridge : university press ) reid , m. a. , & wilson , c. d. 2005 , , 625 , 891 reid , m. a. , & wilson , c. d. 2005 , , submitted salpeter , e. e. 1955 , , 121 , 161 scalo , j. 1998 , in asp conf . 142 , the stellar initial mass function proceedings , ed . g. gilmore & d. howell ( san francisco : asp ) , 201 testi , l. & sargent , a. i. 1998 , , 508 , l91 tilley , d. a. & pudritz , r. e. 2004 , , 353 , 769 tothill , n. f. h. , white , g. j. , matthews , h. e. , mccutcheon , w. h. , mccaughrean , m. j. , kenworthy , m. a. 2002 , , 580 , 285 williams , j. p. , de geus , e. j. , & blitz , l. 1994 , , 428 , 693 wynn - williams , c. g. , becklin , e. e. , & neugebauer , g. 1974 , , 187 , 473 zinnecker , h. 1984 , , 210 , 43

fitting all of the regions with a double power law , we find the mean power law exponent at the high - mass end of each mass function is , consistent with the salpeter result of . this result is consistent with the hypothesis that the clump mass distribution is determined by a highly stochastic process , such as turbulent fragmentation .

we investigate the mass function of cold , dusty clumps in 11 low- and high - mass star - forming regions . using a homogeneous fitting technique , we analyze the shape of each region s clump mass function and examine the commonalities among them . we find that the submillimeter continuum clump mass function in low - mass star - forming regions is typically best fit by a lognormal distribution , while that in high - mass star - forming regions is better fit by a double power law . a single power law clump mass distribution is ruled out in all cases . fitting all of the regions with a double power law , we find the mean power law exponent at the high - mass end of each mass function is , consistent with the salpeter result of . we find no region - to - region trend in with the mass scale of the clumps in a given region , as characterized by their median mass . similarly , non non - parametric tests show that the _ shape _ of the clump mass function does not change much from region to region , despite the obvious changes in the intrinsic mass scale . this result is consistent with the hypothesis that the clump mass distribution is determined by a highly stochastic process , such as turbulent fragmentation . it may also suggest that the data reduction and analysis techniques strongly affect the shape of the derived mass function .

0904.3096

i

the rigorous , statistical confirmation of bimodality within the luminous ( @xmath0 mag ) , nearby galaxy population has proven a key result to emerge from modern wide - field imaging surveys implying the existence of two principal evolutionary pathways for bright systems . this bimodality is clearly evident in the distribution of local galaxies in various _ ( i.e. , total ) observable pairs , including color - magnitude @xcite , concentration ( log @xmath14)-magnitude is used exclusively to represent the _ global _ srsic index , i.e. , the inverse - exponent in the best - fitting , single srsic function to the total galaxy light profile . in the context of our two - component model , where only the central excess above an outer exponential ( i.e. , the bulge ) is fit with a srsic function , the corresponding index will be denoted @xmath15 . ] @xcite and global color - concentration ( log @xmath14 ) @xcite . importantly , many galaxies also display distinct , identifiable structural components frequently ( in massive systems ) a central _ bulge _ and a surrounding _ disc _ @xcite , as well as bars , nuclei , and spiral arms . hierarchical clustering @xcite , the predominant theory of galaxy formation , postulates the existence of two distinct structural formation mechanisms the cooling of gas inside rotating dark matter halos to form _ discs _ @xcite and the merging of similar - sized discs to form _ spheroids _ ( i.e. , ellipticals and classical _ bulges _ ) @xcite . hence , understanding the role of structure in shaping the observed global bimodality may prove crucial to understanding a range of galaxy formation processes . using the millennium galaxy catalogue ( mgc , @xcite ) of 10,095 galaxies , @xcite revealed a clear relationship between visual morphological type and position in the global color - concentration plane . specifically , e / s0s dominate the red , high-@xmath14 ( centrally - concentrated ) peak , sd / irrs dominate the blue , low-@xmath14 ( diffuse ) peak , and sa - sc galaxy types span both . the authors proposed that this relationship derives from the two - component nature of galaxies , and that objects falling between the two peaks of the global bimodality result from the mixing of separate red , compact , bulge and blue , diffuse , disc components in varying degrees . @xcite challenged this hypothesis based upon a sample of 39 s0-sc galaxies with high - resolution , hst imaging . specifically , they recovered a correlation between galaxy color and ( visually - classified ) bulge type , such that classical bulge systems are globally red ( i.e. , also have red discs ) and pseudobulge systems are globally blue , regardless of the bulge - to - total flux ratio . here we further explore the origin of the color - concentration bimodality using the results of allen et al.s ( 2006 ) bulge - disc decomposition of 10,095 bright galaxies in the mgc . in section [ data ] we review the mgc structural dataset and describe the construction of a robust sample , supplemented with rest - frame component colors . in section [ results ] we contrast the global color - concentration distributions of one - component and two - component galaxies ; identify key structural types and construct their luminosity functions ; and examine the relationship between bulge and disc colors . finally , in section [ discussion ] we summarize our conclusions , discuss our results in light of contemporary galaxy formation theory , and reflect upon the challenges facing low resolution , automated structural decomposition studies . unless otherwise stated , all magnitudes are given in the ab system and a cosmological model with @xmath16 , @xmath17 and @xmath18 km s@xmath19 mpc@xmath19 is used throughout .

we investigate the origin of the galaxy color - concentration bimodality at the bright - end of the luminosity function ( mag ) with regard to the bulge - disc nature of galaxies . via ( 2d ) finally , within the two - component population we confirm a previously - reported correlation between bulge and disc color ( with a mean offset of only mag ) .

we investigate the origin of the galaxy color - concentration bimodality at the bright - end of the luminosity function ( mag ) with regard to the bulge - disc nature of galaxies . via ( 2d ) surface brightness profile modeling with gim2d , we subdivide the local galaxy population in the millennium galaxy catalogue into one - component and two - component systems . we reveal that one - component ( elliptical and disc - only ) systems define the two peaks of the galaxy color - concentration distribution ( with total stellar mass densities of and mpc respectively ) , while two - component systems contribute to both a bridging population and the red , concentrated peak ( with total stellar mass densities of and mpc respectively ) . moreover , luminous , ` bulge - less , red discs ' and ` disc - less , blue bulges ' ( blue ellipticals ) are exceptionally rare ( with _ volume_-densities of and mpc respectively ) . finally , within the two - component population we confirm a previously - reported correlation between bulge and disc color ( with a mean offset of only mag ) .

0904.3096

c

our key conclusions may be summarized as follows . via bulge - disc decomposition and quantitative morphological classification ( i.e. , the logical filter in @xcite ) of luminous ( @xmath0 mag ) , nearby ( @xmath35 ) galaxies in the mgc , we have demonstrated that : \(i ) one - component systems ( predominantly elliptical and disc - only galaxies ) display strong bimodality in the color - concentration plane , contributing to a red , high srsic index peak and a blue , low srsic index peak respectively ( with total stellar mass densities of @xmath1 and @xmath2 @xmath3 @xmath4 @xmath5 @xmath6 mpc@xmath7 in each ) ; \(ii ) luminous , ` bulge - less , red discs ' and ` disc - less , blue bulges ' ( i.e. , blue ellipticals ) are rare ; ( with volume - densities of @xmath10 and @xmath8 @xmath3 @xmath11 @xmath12 mpc@xmath7 respectively ) ; \(v ) the two - component systems may be subdivided in a physically - motivated manner at @xmath134 into bridging ( late - type disc ) and red peak ( early - type disc ) populations ( with total stellar mass densities of @xmath8 and @xmath9 @xmath3 @xmath4 @xmath5 @xmath6 mpc@xmath7 in each ) . we now investigate how these results compare against other recent studies of galaxy structure , and discuss their interpretation within the hierarchical clustering scenario of galaxy formation , focussing on elliptical , disc - only , and bulge - plus - disc systems in turn . finally , we outline future work , and discuss the challenges facing future low resolution , automated structural decomposition campaigns . the red colors and highly centrally - concentrated light profiles of luminous ellipticals in the mgc are consistent with many other observational studies , including a large sample of elliptical galaxies in the sdss selected via a quantitative morphological approach and examined by @xcite . moreover , these properties are broadly consistent with the modern picture of hierarchical formation in which bright ellipticals are assembled at late epochs via ` dry mergers ' with other early - type systems @xcite . only their progenitors ( i.e. , lower luminosity / mass ellipticals ) are built up early via similar - sized disc mergers as in the original hierarchical model @xcite . the modern scenario is supported by direct observations of early - type mergers at intermediate redshifts @xcite , and n - body simulations confirming that ` dry mergers ' can reproduce the structural and kinematic properties of nearby ellipticals @xcite and preserve the fundamental plane @xcite . the ` dry merger ' scenario is also purported to account for the observed build up of mass on the red sequence since @xmath135 @xcite . however , studies showing minimal evolution of the early - type stellar mass - size relation @xcite not preserved by ` dry merging ' @xcite and constraints on the frequency of recent merging in luminous galaxies from pair counts and asymmetry indices @xcite challenge this hypothesis , suggesting a greater role for ( non - merger ) environmental processes in the recent evolution of the red sequence . the study of galaxy structure via automated bulge - disc decomposition of large , intermediate - to - high redshift datasets , followed by comparison against local samples such as the mgc , may enable the degeneracy between early - type , bulge - plus - disc ( s0 ) and predominantly elliptical ( e ) systems implicit in studies of the ` red sequence ' to be broken thereby providing more accurate constraints on elliptical galaxy evolution . however , the handling of ` false disc ' candidates ( see section [ false ] ) requires improvement . in the meantime , the mgc elliptical population should serve as a key local benchmark , which semi - analytical models must be able to reproduce whilst simultaneously accounting for the properties of disc - only and bulge - plus - disc galaxies as well . the blue colors and diffuse ( i.e. , low-@xmath14 ) light profiles of predominantly disc - only systems in the mgc are also consistent with previous observations of disc - only galaxies , including a large sample of bulge - less , edge - on discs identified in the sdss by @xcite . these properties are also qualitatively consistent with expectations from the hierarchical formation scenario in which disc - dominated galaxies form early , but experience a passive evolutionary history @xcite . however , the prevalence of disc - only systems in the local universe is difficult to reconcile with the expected merger history of galaxies in cdm cosmologies . specifically , in our analysis of the mgc data we identify disc - only systems as contributing @xmath2430% of the total stellar mass in nearby disc galaxies , which is comparable to the number reported by @xcite . in a theoretical study of halo merger histories in a @xmath136cdm universe , @xcite reveal that the observed frequency of bulgeless discs can only be reconciled within the hierarhical formation context provided spheroid production only occurs in mergers involving mass ratios greater than 0.3 . moreover , @xcite reveal equivalent limits on the frequency of minor mergers , which are expected to fuel central star - formation , leading to the creation of pseudobulges @xcite . one may question whether these disc - only galaxies identified in the mgc are indeed entirely ` bulge - less ' , or whether they simply possess very faint ` bulges ' , insignificantly brighter in central surface brightness than the discs in which they are embedded . this is indeed possible given the limitations of our photometric decomposition pipeline @xcite , and we further note the potential for dust extinction to obscure compact bulges @xcite . nevertheless , even if a population of very faint bulges is hiding within our disc - only population , their properties are vastly different to those of the bright , high surface brightness classical bulges predicted by the hierarhical clustering model @xcite . we also note that in a high resolution study of 19 nearby late - type discs , @xcite observed that most of their sample could be well - fit using a single srsic profile model , and the vast majority of central flux excesses detected could not be attributed to ` what one would generally consider to be a bulge component ' . similarly , @xcite point out that of the four largest disc galaxies in the local group , two ( m33 and the lmc ) do not possess convincing classical bulges . however , it is certainly important to account for observational limitations when comparing output from semi - analytical simulations against empirical datasets in order to derive robust conclusions . one example of how this may be achieved is the analysis pipeline developed by @xcite to generate realistic simulated galaxy images from model predictions , which may be used to compute ` observed ' structural parameters . the close relationship between the bulge and disc colors of two - component galaxies as well as recent low resolution @xcite and high resolution studies @xcite revealing the disc - like nature of many blue _ and _ red bulges points towards a scenario in which _ both _ secular evolution and merging play key roles in bulge formation , in contrast to the conventional hierarchical view @xcite . recent n - body simulations @xcite certainly indicate that secular evolutionary processes are efficient at establishing pseudobulge - like , central mass concentrations . however , the distinction between classical bulge and pseudobulge systems may not be as clear as is often suggested based upon sauron observations of 24 sa / sab galaxies , @xcite report the co - existence of both an old , velocity - dispersion supported ` classical ' component and a young , rotationally - supported ` pseudobulge ' component within the nuclei of these early - type discs . high redshift observations offer some further important clues as to the formation pathways of bulge - plus - disc galaxies , although cosmic variance contributes a large source of uncertainty to the results . for instance , from the structural decomposition of 248 galaxies at @xmath137 , @xcite reveal that the correlation betweeen bulge and global color is in place by intermediate redshifts . they also identify 60% of their bulges as displaying red colors consistent with passively - evolving stellar populations , and 40% as displaying bluer colors indicative of more recent star - formation . they speculate that the formation of red bulges coincided with a truncation of galaxy star - formation that did not destroy the disc . indeed , the role of black hole and agn formation @xcite can not be overlooked in any complete model of bulge formation given the relationships between bulge and black hole properties @xcite . in contrast to the results of @xcite , @xcite report a much higher fraction ( 85% ) of red bulges at high redshift in their sample of 71 cluster and 21 field galaxies at @xmath138 , more consistent with a merger - built origin . however , the observed fraction is perhaps influenced by their selection of luminous bulges ( rather than simply globally luminous galaxies ) . [ [ future - work - and - challenges - for - low - resolution - automated - structural - decomposition - studies ] ] future work , and challenges for low resolution , automated structural decomposition studies + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + semi - analytical models of hierarchical galaxy formation ( e.g. @xcite ) now have the power to trace the formation and evolution of both bulge and disc components separately @xcite . moreover , wide - field galaxy surveys ( e.g. sdss , mgc , gems ) now achieve sufficient survey volumes and imaging resolutions to facilitate large - scale , automated / semi - automated , bulge - disc decomposition studies @xcite . a number of recent studies also offer important albiet relatively small sample benchmarks of galaxy structure in the intermediate - to - high redshift universe @xcite . hence , there currently exist unprecedented opportunities to unify theory and observation via detailed statistical studies of galaxies by structural type and component . however , many observational challenges in this endeavor still remain . advanced , automated , data processing and quality control procedures are required to account for the impact of secondary structural features ( e.g. bars and/or bright knots of active star - formation ) during bulge - disc decompositions whilst ensuring meaningful output . automation of these processes is mandatory due to the vast sample sizes necessary to successfully limit cosmic variance uncertainties , provide accurate statistical constraints on the relevant structural parameters , and enable investigation of the role of environment and mass . finally , we note that a meaningful comparison between theory and observation will also require careful handling of the relevant observational selection biases and measurement errors , and the use of quantitative classification techniques for defining equivalent morphological sub - types . fortunately , quality , wide - field , near - ir survey data is becoming increasingly available ( e.g. ukidss , gama ) , which should help to limit the impact of irregular star - formation features and dust attenuation . furthermore , the next generation of bulge - disc decomposition software is expected to introduce many new capabilities ( as anticipated in the up - coming galfit v3.0 ) . the millennium galaxy catalogue consists of imaging data from the isaac newton telescope and spectroscopic data from the anglo australian telescope , the anu 2.3-m , the eso new technology telescope , the telescopio nazionale galileo and the gemini north telescope . the survey has been supported through grants from the particle physics and astronomy research council ( uk ) and the australian research council ( aus ) . the data and data products are publicly available from http://www.eso.org/jliske/mgc/ or on request from j.l . or s.p.d . e.c . acknowledges partial financial support from the australian research council discovery project grant dp0451426 . adelman - mccarthy , j. k. , et al . 2007 , , 172 , 2 , 634 - 644 allen , p. d. , driver , s. p. , graham , a. w. , cameron , e. , liske , j. , & de propris , r. 2006 , , 371 , 2 - 18 almeida , c. , baugh , c. m. , & lacey , c. g. 2007 , , 376 , 4 , 1711 - 1726 andredakis , y. c. , peletier , r. f. , & balcells , m. 1995 , , 275 , 3 , 874 athanassoula , e. 2005 , , 358 , 4 , 1477 - 1488 balcells , m. , graham , a. w. , domngues - palmero , l. , & peletier , r. f. 2003 , , 582 , l79-l82 baldry , i. k. , glazebrook , k. , brinkmann , j. , ivezi . , lupton , r. h. , nichol , r. c. , & szalay , a. s. 2004 , , 600 , 681 - 694 ball , n. m. , loveday , j. , brunner , r. j. , baldry , i. k. , & brinkmann , j. 2006 , , 373 , 2 , 845 balogh , m. l. , baldry , i. k. , nichol , r. , miller , c. , bower , r. , & glazebrook , k. 2004 , , 615 , 2 , 101 - 104 barden , m. , et al . 2005 , , 635 , 2 , 959 barnes , j. 1992 , , 393 , 2 , 484 - 507 baugh , c. m. , cole , s. , & frenk , c. s. 1996 , , 283 , 4 , 1361 - 1378 bell , e. f. , mcintosh , d. h. , katz , n. , & weinberg , m. d. 2003 , , 149 , 289 - 312 bell , e. f. , et al . 2004 , , 608 , 752 bernardi , m. , et al . 2003 , , 125 , 4 , 1817 - 1848 bernardi , m. , et al . 2003 , , 125 , 4 , 1849 - 1865 bernardi , m. , et al . 2003 , , 125 , 4 , 1866 - 1881 bernardi , m. , et al . 2003 , , 125 , 4 , 1882 - 1896 blanton , m. r. , et al . 2003 , , 594 , 186 - 207 blanton , m. r. 2006 , , 648 , 1 , 268 - 280 blanton , m. r. , & roweis , s. 2007 , , 133 , 734 - 754 beker , t. , stanek , r. , & van der marel , r. p. 2003 , , 125 , 3 , 1073 - 1086 bournaud , f. , combes , f. , & semelin , b. 2005 , , 364 , 1 , l18-l22 boylan - kolchin , m. , ma , c .- p . , & quataert , e. 2005 , , 362 , 1 , 184 - 196 cameron , e. , & driver , s. p. 2007 , , 377 , 1 , 523 - 534 carollo , c. m. , stiavelli , m. , de zeeuw , p. t. , seigar , m. , & dejonghe , h. 2001 , , 546 , 216 - 222 carollo , c. m. , stiavelli , m. , seigar , m. , de zeeuw , p. t. , dejonghe , h. 2002 , , 123 , 1 , 159 - 183 cole , s. , hatton , s. , weinberg , d. h. , & frenk , c. s. 1998 , , 300 , 4 , 945 - 966 cole , s. , lacey , c. g. , baugh , c. m. , & frenk , c. s. 2000 , , 319 , 1 , 168 - 204 colless , m. , et al . 2001 , , 328 , 4 , 1039 - 1063 combes , f. 2008 , preprint ( arxiv:0801.0343 ) cowie , l. l. , songailia , a. , hu , e. m. , & cohen , j. g. 1996 , , 112 , 839 debattista , v. p. , mayer , l. , carollo , c. m. , moore , b. , wadsley , j. , & quinn , t. 2006 , , 645 , 1 , 209 - 227 de jong , r. s. , & lacey , c. 2000 , , 545 , 2 , 781 - 797 de lapparent , v. 2003 , , 408,845 - 872 de lucia , g. , springel , v. , white , s. d. m. , croton , d. , & kauffmann , g. 2006 , , 366 , 2 , 499 - 509 de propris , r. , conselice , c. , liske , j. , driver , s. p. , patton , d. r. , graham , a. w. , & allen , p. d. 2007 , , 666 , 1 , 212 - 221 de souza , r. e. , gadotti , d. a. , & dos anjos , s. 2004 , , 153 , 411 de vaucouleurs , g. 1959 , handbuch der physik , 53 , 311 domnguez - palmero , l. , & balcells , m. 2008 , , 489 , 3 , 1003 - 1014 driver , s. p. , liske , j. , cross , n. j. g. , de propris , r. , & allen , p. d. 2005 , , 360 , 81 - 103 driver , s. p. , et al . 2006 , , 268 , 414 - 434 driver , s. p. , allen , p. d. , liske , j. , & graham , a. w. 2007 , , 657 , l85-l88 driver , s. p. , popescu , c. , tuffs , r. j. , liske , j. , graham , a. w. , allen , p. , & de propris , r. 2007 , , 379 , 3 , 1022 - 1036 driver , s. p. , popescu , c. c. , tuffs , r. j. , graham , a. w. , liske , j. , & baldry , i. 2008 , apj , 678 , 2 , l101-l104 drory , n. , & fisher , d. b. 2007 , , 664 , 640 - 649 erwin , p. , beltrn , j. c. v. , graham , a. w. , & beckman , j. e. 2003 , , 597 , 2 , 929 - 947 eskridge , p. b. , et al . 2000 , , 119 , 2 , 536 - 544 fall , s. m. , & efstathiou , g. 1980 , , 193 , 189 - 206 ferrerese , l. , & merritt , d. 2000 , , 539 , 1 , l9-l12 fisher , d. b. 2006 , , 642 , l17-l20 fisher , d. b. , & drory , n. 2008 , , 136 , 2 , 773 - 839 freeman , k. c. 1970 , , 160 , 811 gadotti , d. a. 2008 , , 384 , 1 , 420 - 439 gadotti , d. a. 2008 , preprint ( arxiv:0810.1953 ) gebhardt , k. , et al . 2000 , , 539 , 1 , l13-l16 governato , f. , willman , b. , mayer , l. , brooks , a. , stinson , g. , valenzuela , o. , wadsley , j. , & quinn , t. 2007 , , 374 , 4 , 1479 - 1494 graham , a. w. 2001 , , 121 , 820 graham , a. g. & guzmn , r. 2003 , , 125 , 6 , 2936 - 2950 graham , a. w. , & driver , s. p. 2005 , pasa , 22 , 2 , 118 - 127 graham , a. w. & driver , s. p. 2007 , , 380 , 1 , l15-l19 gray , m. e. , et al . 2008 , preprint ( arxiv:0811.3890 ) gunn , j. e. , & gott , j. r. iii 1972 , , 176 , 1 gunn , j. e. , et al . 1998 , , 116 , 6 , 3040 - 3081 gutirrez , c. m. , trujillo , i. , aguerri , j. a. l. , graham , a. w. , & caon , n. 2004 , , 602 , 2 , 664 - 677 hernquist , l. , & mihos , j. c. 1995 , , 448 , 41 hussler , b. , et al . 2007 , , 172 , 2 , 615 - 633 jogee , s. , kenney , j. d. p. , & smith , b. j. 1999 , , 526,2 , 665 - 682 kauffmann , g. , colberg , j. m. , antonaldo , d. , & white , s.d.m . 1999 , , 303 , 188 kautsch , s. j. , grebel , e. k. , barazza , f. d. , & gallagher , j. s. , iii 2006 , , 445 , 2 , 765 - 778 khochfar , s. , & burkert , a. 2003 , , 597 , 2 , l117-l120 koda , j. , milosavljevic , m. , shapiro , p. r. 2007 , preprint(arxiv:0711.3014 ) koo , d. c. , datta , s. , willner , c. n. a. , simard , l. , tran , k .- v . , & i m , m. 2005 , , 634 , 1 , l5-l8 kormendy , j. , & kennicutt , r. c. , jr . 2004 , , 42 , 1 , 603 - 683 kuchinski , l. e. , terndrup , d. m. , gordon , k. d. , & witt , a. n. 1998 , , 115 , 4 , 1438 - 1461 laurikainen , e. , salo , h. , & buta , r. 2005 , , 362 , 4 , 1319 - 1347 laurikainen , e. , salo , h. , buta , r. , & knapen , j. h. 2007 , , 381 , 1 , 401 - 417 liske , j. , lemon , d. j. , driver , s. p. , cross , n. j. g. , & couch , w. j. 2003 , , 344 , 307 - 324 macarthur , l. a. , courteau , s. , bell , e. , & holtzman , j. a. 2004 , , 152 , 175 - 199 magorrian , j. 1998 , , 115 , 6 , 2285 - 2305 mcintosh , d. h. , et al . 2005 , , 632 , 1 , 191 mo , h. j. , mao , s. , & white , s. d. m. , 1998 , , 295 , 2 , 319 - 336 moore , b. , katz , n. , lake , g. , dressler , a. , & oemler , a. 1996 , , 379 , 613 - 616 naab , t. , & burkert , a. 2003 , , 597 , 2 , 893 - 906 neistein , e. , van den bosch , f. c. , & dekel , a. 2006 , , 372 , 2 , 933 - 948 nipoti , c. , londrillo , p. , & ciotti , l. 2003 , , 342 , 2 , 501 - 512 pahre m. a. , ashby , m. l. n. , fazio g. g. , & willner , s. p. 2004 , , 154 , 229 - 234 peebles , p. j. e. 1969 , , 155 , 393 peletier , r. f. , & balcells , m. 1996 , , 111 , 6 , 2238 peletier , r. f. , et al . 2008 , in iau symposium 245 , formation and evolution of galaxy bulges , ed . bureau , m. , athanassoula , e. , & barbuy , b. ( cambridge , uk : cambridge university press ) , 271 - 276 peng , c. y. , ho , l. c. , impey , c. d. , & rix . 2002 , , 124 , 1 , 266 - 293 phillips , s. , davies , j. i. , & disney , m. j. 1990 , , 242 , 1990 , 235 - 240 poggianti , b. m. 1997 , , 122 , 399 - 407 schlegel , d. j. , finkbeiner , d. p. , & davis , m. 1998 , , 500 , 525 shen , s. , et al . 2003 , , 343 , 3 , 978 simard , l. 1998 , in asp conf . 145 , astronomical data analysis software and systems vii , ed . r. albrecht , r. n. hook , & h. a. bushouse ( san francisco , ca : asp ) , 108 somerville , r. s. , & primack , j. r. 1999 , , 310 , 1087 somerville , r. s. , hopkins , p. f. , cox , t. j. , robertson , b. e. , & hernquist , l. 2008 , , 391 , 2 , 481 - 506 stewart , k. r. , bullock , j. s. , wechsler , r. h. , maller , a. h. , & zentner , a. r. 2008 , , 683 , 2 , 597 - 610 strateva , i. , et al . 2001 , , 122 , 1861 tasca , l. a. m. , & white , s. d. m. 2005 , preprint ( astro - ph/0507249 ) toomre , a. , & toomre , j. 1972 , , 178 , 623 - 666 tran , k .- v . h. , van dokkum , p. , franx , m. , illingworth , g. d. , kelson , d. d. , & schreiber , n. m. f. 2005 , , 627 , 1 , l25-l28 trujillo , i. , graham , a. w. , & caon , n. 2001 , mnras , 326 , 3 , 869 - 876 trujillo , i. , et al . 2004 , , 604 , 2 , 521 - 533 tuffs , r. j. , popescu , c. c. , vlk , h. j. , kylafis , n. d. , & dopita , m. a. 2004 , , 419 , 821 - 835 van den bergh , s. 2007 , , 134 , 1508 - 1514 van dokkum , p. g. , franx , m. , fabricant , d. , kelson , d. d. , & illingworth , g. d. 1999 , , 520 , 2 , l95-l98 van kampen , e. , jimenez , r. , & peacock , j. a. 1999 , , 310 , 1 , 43 - 56 vlahakis , c. , dunne , l. , & eales , s. 2005 , , 364,1253 - 1285 weinzirl , t. , jogee , s. , khochfar , s. , burkert , a. , & kormendy , j. 2008 , preprint ( arxiv:0807.0040 ) white , s. m. , & rees , m. j. 1978 , , 183 , 241 - 358 white , s. m. & frenk , c. s. 1991 , , 379 , 52 wyse , r. f. g. , gilmore , g. , & franx , m. 1997 , , 35 , 637 - 675 this appendix contains real ( mgc ) and model ( gim2d / galfit ) , @xmath23-band images and surface brightness profiles of example galaxies illustrating three problematic fit scenarios false discs ( fig . [ cut ] ) , strong bars ( fig . [ bars ] ) , and bright knots of active star - formation ( fig . [ starform ] ) .

we reveal that one - component ( elliptical and disc - only ) systems define the two peaks of the galaxy color - concentration distribution ( with total stellar mass densities of and mpc respectively ) , while two - component systems contribute to both a bridging population and the red , concentrated peak ( with total stellar mass densities of and mpc respectively ) . moreover , luminous , ` bulge - less , red discs ' and ` disc - less , blue bulges ' ( blue ellipticals ) are exceptionally rare ( with _ volume_-densities of and mpc respectively ) .

we investigate the origin of the galaxy color - concentration bimodality at the bright - end of the luminosity function ( mag ) with regard to the bulge - disc nature of galaxies . via ( 2d ) surface brightness profile modeling with gim2d , we subdivide the local galaxy population in the millennium galaxy catalogue into one - component and two - component systems . we reveal that one - component ( elliptical and disc - only ) systems define the two peaks of the galaxy color - concentration distribution ( with total stellar mass densities of and mpc respectively ) , while two - component systems contribute to both a bridging population and the red , concentrated peak ( with total stellar mass densities of and mpc respectively ) . moreover , luminous , ` bulge - less , red discs ' and ` disc - less , blue bulges ' ( blue ellipticals ) are exceptionally rare ( with _ volume_-densities of and mpc respectively ) . finally , within the two - component population we confirm a previously - reported correlation between bulge and disc color ( with a mean offset of only mag ) .

1302.2196

i

now that the higgs - like particle has been discovered in large hadron collider ( lhc ) @xcite , one of primary interests of particle physics is to understand mechanism of dynamical electroweak symmetry breaking . to settle down the unsolved issues including the hierarchy problem , there have been proposed several promising courses including supersymmetric , composite - higgs and extra - dimensional models . among them , the gauge - higgs unification with extra dimensions @xcite produces brilliant dynamics of gauge symmetry breaking , called the hosotani mechanism @xcite , with the higgs particle as an extra - dimensional component of the gauge field : when adjoint fermions are introduced with periodic boundary condition ( pbc ) in gauge theory with a compact dimension , the compact - space component of the gauge field can develop a non - zero vacuum expectation value ( vev ) , which breaks the gauge symmetry to its subgroup spontaneously . this phenomenon originates in the non - abelian aharonov - bohm effect . there have been proposed a number of bsm models directly and indirectly based on this mechanism @xcite recently , the same phenomenon has been observed in a different context . as well - known , the imaginary time dimension is compacted in the finite - temperature ( quantum chromodynamics ) qcd . when the adjoint fermion is introduced with pbc in the theory , it was shown that exotic phases appear @xcite , where the color trace of polyakov line takes non - trivial vev leading to the dynamical gauge symmetry breaking . this can be interpreted as @xmath3 realization of the hosotani mechanism . further study is now required to understand detailed properties and phase diagram for this case . as for the five - dimensional gauge theory on @xmath4 , lattice simulation is still at the stage to understand the nature of 5d pure yang - mills theory . first attempt was done in ref . @xcite and recent progress was shown in ref . @xcite . at the present , we have no detailed investigation on the phase structure of the five - dimensional gauge theory with dynamical quarks . the purpose of our work is to understand properties of gauge theories with quarks on @xmath3 and @xmath4 by using effective theories and show a guideline for further lattice simulations . we focus on the phase structure in @xmath0 gauge theory by mainly using the perturbative one - loop effective potential . when we look into chiral properties , the polyakov - loop - extended nambu jona - lasinio ( pnjl ) model @xcite is introduced . we obtain the phase diagram in the quark - mass and compacted - size space for several different choices of fermion representations and boundary conditions . in the theory with adjoint fermions with pbc , we find rich phase diagram with unusual phases where @xmath0 gauge symmetry is spontaneously broken to @xmath1 ( split phase ) or @xmath2 ( re - confined phase ) . this result is consistent with the recent lattice simulations @xcite and the perturbative calculations for massless quarks @xcite . we show that chiral condensate is gradually decreased and the chiral symmetry is slowly restored with the compacted size being decreased although small chiral transitions coincide with the deconfined / split and split / reconfined transitions . we also study phase diagram for the case with both fundamental and adjoint quarks , and show that the split phase becomes more dominant as a result of the explicit breaking of @xmath5 center symmetry . this result indicates that the @xmath6 phase , which is of significance in terms of phenomenology , can be controlled by adjusting the number of fundamental flavors . in this case we point out that another unusual ( @xmath2 ) phase with negative vev of color - traced polyakov loop emerges , which we call pseudo - reconfined phase " . we note similar investigation on the phase diagram of compact - space gauge theory with pbc fermions were shown in @xcite , where the authors focus on the volume independence of the vacuum structure from the viewpoint of the large n reduction @xcite . in order to reproduce the confined phase at low temperature , they used the gluon effective potentials with the mass - dimension parameter , which leads to explicit gauge symmetry breaking . since these effective potentials do not suit our purpose of studying spontaneous gauge symmetry breaking due to the hosotani mechanism , we mainly use setups with manifest gauge symmetry . it is also notable that gauge symmetry breaking for all clasical lie groups with pbc matters are classified from topological viewpoints in @xcite . this paper is organized as following . in sec . [ sec : ep ] , we show our setups including the one - loop potential and the pnjl model . [ sec : ps4 ] shows our numerical results for four dimensional cases . [ sec : ps5 ] shows the results for five - dimensional cases . in sec . [ sec : ob ] we discuss how our predictions can be checked in the lattice simulations . [ sec : sum ] is devoted to summary .

our result is qualitatively consistent with the recent lattice calculations . when fundamental quarks are introduced in addition to adjoint quarks , the split phase becomes more dominant and larger as a result of explicit center symmetry breaking . we study chiral properties in these theories and show that chiral condensate gradually decreases and chiral symmetry is slowly restored as the size of the compact dimension is decreased .

we investigate the phase structure of gauge theory in four and five dimensions with one compact dimension by using perturbative one - loop and pnjl - model - based effective potentials , with emphasis on spontaneous gauge symmetry breaking . when adjoint matter with the periodic boundary condition is introduced , we have rich phase structure in the quark - mass and compact - size space with gauge - symmetry - broken phases , called the split and the re - confined phases . our result is qualitatively consistent with the recent lattice calculations . when fundamental quarks are introduced in addition to adjoint quarks , the split phase becomes more dominant and larger as a result of explicit center symmetry breaking . we also show that another phase ( pseudo - reconfined phase ) with negative vacuum expectation value of polyakov loop exists in this case . we study chiral properties in these theories and show that chiral condensate gradually decreases and chiral symmetry is slowly restored as the size of the compact dimension is decreased .

1302.2196

i

in this paper we have studied the phase diagram for @xmath0 gauge theories with a compact spatial dimension by using the effective models , with emphasis on the dynamical gauge symmetry breaking . we show that introduction of adjoint matter with periodic boundary condition leads to the unusual phases with spontaneous gauge symmetry breaking , whose ranges are controlled by introducing fundamental matter . we also study chiral properties in these theories and show that the chiral condensate remains nonzero even at a small compacted size . in sec . [ sec : ep ] , we developed our setup based on one - loop effective potential and four - point fermion interactions . the effective potential is composed of the gluon , quark and chiral sectors . the total effective potential corresponds to that of the pnjl model with one - loop gluon potential . this setup is effective enough to investigate vacuum structure and chiral properties at weak - coupling or small size of the compact dimension . in sec . [ sec : ps4 ] , we elucidated the vacuum and phase structure in @xmath0 gauge theory on @xmath3 . the theory with pbc adjoint quarks has three different phases in the @xmath86-@xmath87 space , including the deconfined phase ( @xmath0 , nonzero @xmath142 ) , the split phase ( @xmath1 , nonzero @xmath142 ) and the re - confined phase ( @xmath2 , zero @xmath142 with nontrivial global minima ) . the configuration of these phases in the phase diagram is consistent with that of the lattice calculations although we have no confined phase . by using the pnjl effective potential , we argued that chiral symmetry is slowly restored without clear phase transition when the size of the compact dimension is decreased . in this section we also studied vacuum and phase structure for the case with both fundamental and adjoint matters , and showed that the split phase is generically widened by adding pbc fundamental quarks . we consider that it is because one of the three possible minima for the split phase becomes more stable due to the center symmetry breaking . we showed that another @xmath2 phase with a negative value of @xmath142 emerges in this case ( pseudo - reconfined phase ) . in sec . [ sec : ps5 ] , we studied the vacuum and phase structure in @xmath0 gauge theory on @xmath4 . in the five - dimensional case we concentrate on the one - loop part of the effective potential the theory with pbc adjoint quarks again has the split ( @xmath1 ) and re - confined ( @xmath2 ) phases . introduction of fundamental quarks works to enlarge the split phase more effectively than the four - dimensional case . especially in the case with one adjoint and one fundamental quarks without parity pairs , the split phase overcomes the pseudo - reconfined phase and becomes a unique gauge - symmetry - broken phase . in sec . [ sec : ob ] , we discuss observables comparable to the lattice simulations . we list up observables including particle mass spectrum , in particular gauge boson mass ( lowest kk spectrum ) , polyakov - loop in the compact dimension , constituent mass . they can be good indications of exotic phase and properties both in the existing and on - going simulations . all through this paper , we treat pbc and apbc cases in a parallel manner . we note that the reference @xcite argues that gauge theory with pbc fermions has no thermal fluctuation , and thermal interpretation is inappropriate in such a case . this means that all the results here should be understood as topological phenomena . in the end of the paper , we discuss whether the lattice simulation can check our predictions . one of our main results is that enlargement of the split phase in the presence of fundamental fermions . this property would be observed in the on - going lattice simulations on four - dimesional gauge theory with a compact direction @xcite . the pseudo - reconfined phase can be also observed where the vev of polyakov loop becomes negative but different from that of the split phase . on the other hand , it seems difficult to show the first - order phase transition between the pseudo - reconfined and split phases . the lattice calculation can check whether chiral condensate remains finite in the re - confined phase even at a very small compacted size . the small chiral transitions coinciding with the gauge - symmetry phase transitions are subtle . if the lattice simulation succeeds to measure chiral susceptibility with high precision , this phenomena may be able to be observed . during preparing this draft , the collaboration @xcite kindly informed us that it also performed perturbative calculations on the phase diagram in gauge theory on @xmath3 and @xmath4 . it could be valuable for readers to compare the results from the two independent groups . the authors are grateful to e. itou for giving them chances to have interest in the present topics and reading the draft carefully . they are thankful to y. hosotani , h. hatanaka and h. kouno for their careful reading of this manuscript and valuable comments . they also thank g. cossu and j. noaki for the kind co - operation . k. k. thanks h. nishimura for useful comments . is supported by riken special postdoctoral researchers program . is supported by grand - in - aid for the japan society for promotion of science ( jsps ) postdoctoral fellows for research abroad(no.24 - 8 ) .

we investigate the phase structure of gauge theory in four and five dimensions with one compact dimension by using perturbative one - loop and pnjl - model - based effective potentials , with emphasis on spontaneous gauge symmetry breaking . when adjoint matter with the periodic boundary condition is introduced , we have rich phase structure in the quark - mass and compact - size space with gauge - symmetry - broken phases , called the split and the re - confined phases . we also show that another phase ( pseudo - reconfined phase ) with negative vacuum expectation value of polyakov loop exists in this case .

we investigate the phase structure of gauge theory in four and five dimensions with one compact dimension by using perturbative one - loop and pnjl - model - based effective potentials , with emphasis on spontaneous gauge symmetry breaking . when adjoint matter with the periodic boundary condition is introduced , we have rich phase structure in the quark - mass and compact - size space with gauge - symmetry - broken phases , called the split and the re - confined phases . our result is qualitatively consistent with the recent lattice calculations . when fundamental quarks are introduced in addition to adjoint quarks , the split phase becomes more dominant and larger as a result of explicit center symmetry breaking . we also show that another phase ( pseudo - reconfined phase ) with negative vacuum expectation value of polyakov loop exists in this case . we study chiral properties in these theories and show that chiral condensate gradually decreases and chiral symmetry is slowly restored as the size of the compact dimension is decreased .

0812.1851

i

the astounding range of experimental and theoretical studies performed on carbon nanotubes @xcite has revealed a spectrum of physics characteristic of strongly correlated low - dimensional electronic systems @xcite . the underlying graphene lattice structure of these tubes uniquely affects band structure , effective dimensionality , coulomb interaction effects , and the quantum dot behavior exhibited by short nanotube segments . the band structure shows differing behavior depending on various factors such as chirality , applied gate potentials , boundary conditions at the tube ends and mechanical stress @xcite . in single - walled armchair nanotubes ( swnt ) @xcite , which are the entities of interest here , gapless linearly dispersing modes endow the nanotube with its peculiar quantum wire properties . as described theoretically and ascertained experimentally , interactions within the modes of this effectively one - dimensional system cause it to behave as a luttinger liquid characterized by non - ohmic conductances @xcite . tubes placed between tunnel barriers act as quantum dots @xcite , which , while displaying zero dimensional physics such as coulomb blockade behavior , retain some higher dimensional traits such as hosting plasmons typical of one dimension and band degrees of freedom attributed to the underlying graphene lattice . potentially invaluable to applications , these nanotube quantum dots have been proposed as elements of quantum devices and the quantum states of blockaded electrons have been regarded as candidates for units of quantum information @xcite . in each of these aspects , the presence of applied fields can dramatically alter the nanotube s behavior ; here we present an extensive study of the effects of electric and magnetic fields applied transversally to the axis of the nanotube . at the level of the band structure , it has been shown that a parallel magnetic field can have the striking effect of converting a metallic tube to a semiconducting one by way of inducing a gap @xcite , and vice - versa , an effect discernible in conductance , coulomb blockade and scanning tunneling microscope ( stm ) measurements . here , instead of a parallel field , we discuss transverse field configurations ( both electric and magnetic ) and the conditions under which a band gap opens up or the spectrum remains gapless in armchair swnts . in the latter case , we demonstrate , via band - structure calculations , simultaneous breaking of the valley degeneracy ( of the two distinct dirac points ) , the left - right - mover degeneracy , and the particle - hole symmetry . moreover , the fields yield a non - negligible reduction in the fermi velocity of conduction electrons traveling along the tube . we show that for certain configurations of fields , the ground state of the tube can even be made to carry finite current . transverse fields provide an excellent means of altering the ratio of interaction strength to the fermi energy in swnts . this makes nanotubes potentially the only systems to date in which the associated luttinger liquid physics can be tuned in a controlled fashion . as described in previous work , either an electric field @xcite or a magnetic field @xcite alone suffices to change the value of the luttinger liquid parameter from that measured in field - free environments . the magnitude of the electric fields required to bring about a significant change are well within current experimental reach @xcite . here , we find that our approach reproduces these results . we show that such a tuning of luttinger parameters can mediate a transition from the system showing tendencies towards spin - density - wave ( sdw ) ordering to that of charge - density - wave ( cdw ) ordering . furthermore , in addition to the tuning of the luttinger parameter presented in previous works for the net charge density @xcite , we find that luttinger - type interactions become manifest in modes associated with the density differences between nanotube bands as well . thus we predict that akin to spin - charge separation , transverse fields can induce a spin - charge - band separation wherein the three degrees of freedom move at different velocities . the above results are discussed in the case of an infinite system . for short tubes or finite length segments formed by tunnel barriers , boundary effects need to be taken into account . we find that applied fields influence multiple aspects of short nanotubes . first , fields can alter the single - particle energy level spacing of the tube . here , we carefully account for the effect of the tube ends in the case that the left and right movers travel at different speeds . second , the charging energies become field dependent , and third , the plasmon spectrum varies in accordance with the first two effects . we have conducted a comprehensive analysis of the short nanotube as a finite - sized luttinger liquid and show how all three effects can be captured . within this description , we discuss the structure of field - dependent coulomb blockade peaks and how the presence of both electric and magnetic fields acts as a means of manipulating quantum states of the dot ( the effect of a magnetic field alone has recently been discussed by bellucci and onorato @xcite ) . ) and electric fields . the carbon atoms belonging to the a and b sublattices are indicated by dark ( blue ) and light ( green ) shading , respectively.,width=8 ] the outline of this paper is as follows . in section ii we present the formulation and results of our band structure calculation . in section iii we formulate an effective one - dimensional hamiltonian which takes into account field effects . we bosonize this hamiltonian , describing interaction effects in terms of luttinger liquid physics . in section iv we investigate the various luttinger liquid phases and the feasibility of using fields to access such phases . in section v we discuss field - tuned quantum dot physics . finally , in section vi we present the highlights of our results and discuss their relevance to experiments .

we investigate the properties of conduction electrons in single - walled armchair carbon nanotubes ( swnt ) in the presence of both transverse electric and magnetic fields . we find that these fields provide a controlled means of tuning low - energy band structure properties such as inducing gaps in the spectrum , breaking various symmetries and altering the fermi velocities . we show that the fields can strongly affect electron - electron interaction , yielding tunable luttinger liquid physics , the possibility of spin - charge - band separation , and a competition between spin - density - wave and charge - density - wave order . for short tubes ,

we investigate the properties of conduction electrons in single - walled armchair carbon nanotubes ( swnt ) in the presence of both transverse electric and magnetic fields . we find that these fields provide a controlled means of tuning low - energy band structure properties such as inducing gaps in the spectrum , breaking various symmetries and altering the fermi velocities . we show that the fields can strongly affect electron - electron interaction , yielding tunable luttinger liquid physics , the possibility of spin - charge - band separation , and a competition between spin - density - wave and charge - density - wave order . for short tubes , the fields can alter boundary conditions and associated single - particle level spacings as well as quantum dot behavior .

1209.3302

i

it has been known that nanostructures based on carbon possess unique mechanical , electrical and optical properties.@xcite among them particular attention has been given to graphene , a two - dimensional sheet of carbon atoms arranged in a hexagonal structure with low - energy electronic excitations described by the dirac equation.@xcite at the present time suspended graphene membranes up to @xmath0 m diameter are produced.@xcite this makes possible to investigate the van der waals and casimir interaction between graphene and different material structures , such as another sheet of graphene , atoms , molecules , dielectric and metallic plates , spheres etc . respective theoretical investigations were performed using the phenomenological density - functional methods,@xcite second - order perturbation theory@xcite and , for multilayered carbon nanostructures , using the lifshitz theory.@xcite to apply the lifshitz theory , one needs the reflection coefficients on graphene over a wide frequency region . it is customary to express the reflection coefficients in terms of the frequency - dependent dielectric permittivity , a concept which is not well defined for one - atom - thick carbon nanostructures . because of this , two models for the reflection coefficients on graphene with no use of dielectric permittivity were proposed , the hydrodynamic one@xcite and the dirac one.@xcite in the framework of the hydrodynamic model , graphene is considered as an infinitesimally thin positively charged sheet , carrying a homogeneous fluid with some mass and negative charge densities . the hydrodynamic model was applied for calculation of the casimir and casimir - polder interactions.@xcite in the framework of the dirac model , it is taken into account that for energies below a few ev the dispersion relation for quasiparticles in graphene is linear with respect to the momentum , whereas it is quadratic in the hydrodynamic model . the reflection coefficients of graphene at zero and nonzero temperature were found in refs . @xcite and @xcite , respectively . some calculations of the casimir - polder graphene - atom interaction were performed at zero temperature using both the hydrodynamic and dirac models.@xcite it should be remembered , however , that both these models are only approximations . as was already mentioned , the hydrodynamic model disregards the dirac character of charge carriers in graphene . as to the dirac model , it extends the linear dispersion relation for quasiparticles to any energy , whereas this property applies only at low energies . because of this , one can conclude that in calculations of the casimir and casimir - polder forces the dirac model of graphene should be applicable at large separations between the test bodies , whereas the hydrodynamic model might work at short separation distances . there is also another approach to the application of the lifshitz theory to graphene . in this approach graphene is characterized by a spatially nonlocal dielectric permittivity depending both on the frequency and the wave vector . different authors express such a dielectric permittivity either through the polarizability of one graphene layer @xcite or in the random phase approximation.@xcite it is well known that thermal casimir effect is a subject of debate and there are different theoretical approaches to its description.@xcite for two graphene sheets in a nonretarded regime it was found@xcite that a relatively large thermal correction to the casimir force at room temperature arises at short separation distances of tens of nanometers . this conclusion was qualitatively confirmed,@xcite using the dirac model of graphene , with an alternative explanation . the reason for the origin of large thermal correction for graphene is that the contribution of all terms with nonzero matsubara frequencies at room temperature becomes small in comparison with the zero - frequency term even at short separations . it was also found@xcite that in graphene - atom casimir - polder interaction the thermal effect depends crucially on the magnitude of a mass gap parameter in the dirac model . specifically , for a nonzero gap there exists an interval of temperatures ( separations ) where the thermal correction remains small with increasing temperature ( separation ) . the possibility of large thermal correction at short separations links the dirac model of graphene to the drude model used in the literature to describe the casimir effect between real metals.@xcite because of this , it is of much interest to investigate the thermal casimir effect in the interaction of graphene with real material bodies made of different materials . in this paper , we calculate the free energy of the casimir interaction between a suspended graphene membrane described by the dirac model and dielectric ( silicon , sapphire ) or metallic ( au , ni ) plates . in so doing materials of the plate are described by realistic dielectric permittivities taking into account the interband transitions of core electrons . we demonstrate that , similar to graphene - atom interaction , the behavior of thermal correction crucially depends on the mass gap parameter @xmath1 of the dirac model . note that although the dirac - type excitations in pristine graphene are gapless , the influence of electron - electron interaction , substrates , defects of structure , and other effects leads to a nonzero mass gap.@xcite specifically , we show that larger is the magnitude of mass gap parameter , wider is the separation ( temperature ) interval , where the thermal correction remains small with increasing separation ( temperature ) . for a metallic plate interacting with graphene , we perform all calculations using both the drude- and plasma - model approaches to the dielectric permittivity of metal . in the case when graphene described by the dirac model interacts with a metallic plate ( either nonmagnetic or magnetic ) the calculation results obtained using both approaches nearly coincide and do not depend on the magnetic properties . in contrast to the case of two drude metals , the thermal correction for a graphene - metal interaction has the same sign as the interaction energy at zero temperature , i.e. , the magnitude of the casimir free energy increases with increasing temperature . note that all results obtained for a free energy in graphene - plate geometry can be reformulated as the casimir force between a material sphere and a graphene sheet using the proximity force approximation ( pfa).@xcite as was recently shown,@xcite the error arising from the use of pfa is less than the ratio of separation distance to sphere radius . in this paper we also compare the predictions of the dirac model for the thermal casimir effect with respective predictions of the hydrodynamic model and discuss the application region of each . specifically , it is shown that the hydrodynamic and dirac models of graphene lead to different results at short separations and to nearly coinciding results at large separations for the casimir free energy of graphene interacting at room temperature with a dielectric plate or with a nonmagnetic metallic plate described by the drude model . for a nonmagnetic metallic plate described by the plasma model or for a magnetic plate the predictions of the hydrodynamic and dirac models of graphene are significantly different at all separations considered and can be discriminated experimentally . at large separations the asymptotic expressions for the casimir free energy of graphene - plate interaction are derived and compared with the computational results . the paper is organized as follows . in sec . ii we present the reflection coefficients of the electromagnetic oscillations on graphene in the dirac and hydrodynamic models . section iii is devoted to the thermal casimir interaction of graphene described by the dirac model with a dielectric plate made of silicon or sapphire . similar results for graphene interacting with a metallic plate made of au and ni are presented in sec . iv . in sec . v the theoretical predictions following from the dirac and hydrodynamic models are compared . our conclusions and discussions are contained in sec .

we investigate the thermal casimir interaction of a suspended graphene described by the dirac model with a plate made of dielectric or metallic materials . we demonstrate that for a graphene with nonzero mass gap parameter the casimir free energy remains nearly constant ( and the thermal correction negligibly small ) over some temperature interval . for the interaction of graphene with metallic plate , these differences vanish with increasing temperature ( separation ) .

we investigate the thermal casimir interaction of a suspended graphene described by the dirac model with a plate made of dielectric or metallic materials . the reflection coefficients on graphene expressed in terms of a temperature - dependent polarization tensor are used . we demonstrate that for a graphene with nonzero mass gap parameter the casimir free energy remains nearly constant ( and the thermal correction negligibly small ) over some temperature interval . for the interaction of graphene with metallic plate , the free energy is nearly the same , irrespective of whether the metal is nonmagnetic or magnetic and whether it is described using the drude- or plasma - model approaches . the free energy computed using the dirac model was compared with that computed using the hydrodynamic model of graphene and big differences accessible for experimental observation have been found . for dielectric and nonmagnetic metallic plates described by the drude model these differences vanish with increasing temperature ( separation ) . however , for nonmagnetic metals described by the plasma model and for magnetic metals , a severe dependence on the chosen theoretical description of graphene remains even at high temperature . in all cases the analytic asymptotic expressions for the free energy at high temperature are obtained and found in a very good agreement with the results of numerical computations .

1209.3302

c

in the foregoing , we have investigated the casimir free energy and the thermal correction to the casimir energy at zero temperature for a suspended graphene sheet interacting with a material plate , either dielectric or metallic . in so doing graphene was described by the fully relativistic dirac model with temperature - dependent polarization tensor . the dielectric properties of the plate were described by the frequency - dependent dielectric permittivity taking into account the interband transitions of core electrons . for a metallic plate both the drude- and plasma - model approaches suggested in the literature have been used . the main novel result obtained for both dielectric and metallic plates is that for graphene with any nonzero mass gap parameter @xmath1 there exists temperature interval where the casimir free energy remains nearly constant . this happens under the condition @xmath171 , which should be satisfied with a large safety margin . if this condition is satisfied , the thermal correction to the casimir energy at zero temperature remains negligibly small . we have also demonstrated that under the condition @xmath172 the thermal correction becomes relatively large . this makes possible large thermal corrections for a graphene sheet interacting with material plate at rather low temperature ( short separations ) . with respect to the interaction with a metallic plate , it was shown that for graphene described by the dirac model the computational results for the free energy are nearly independent on whether the drude- or plasma - model approach to the dielectric permittivity of metal is used . to a large extent the free energy of graphene interacting with metallic plate is also independent on whether metal is nonmagnetic or magnetic if graphene is described by the dirac model . in all cases considered ( dielectric or metallic plate , nonmagnetic or magnetic , described by the drude- or plasma - model approach ) the analytic asymptotic expressions for the casimir free energy at high temperature ( large separations ) have been obtained and compared with the results of numerical computations . the casimir free energies obtained using the dirac model of graphene were compared with those calculated using the hydrodynamic model . it was shown that at moderate temperatures ( separations ) the magnitudes of the free energy computed using the hydrodynamic model of graphene differ significantly from that computed using the dirac model . this can be used for the experimental test of these models . at large separations ( high temeperature ) the theoretical predictions from both models of graphene nearly coincide for a dielectric plate and for a nonmagnetic metallic plate described by the drude model . for a nonmagnetic metallic plate described by the plasma model and for a magnetic plate described by any model the hydrodynamic and dirac descriptions of graphene lead to quite different results for the free energy at large separations ( high temperature ) . this fact can be also used for the experimental test of different models . in this respect the investigation of the interaction between graphene and metamaterials@xcite is also of large interest . we have also found analytic asymptotic expressions for the free energy at high temperature ( large separations ) when graphene described by the hydrodynamic model interacts with a dielectric plate or with a plate made of a nonmagnetic or magnetic metal . in the last two cases both the drude- and plasma - model approaches have been used for a description of the dielectric properties of metal . the calculation results obtained from the asymptotic expressions were found in a very good agreement with the results of numerical computations .

the free energy is nearly the same , irrespective of whether the metal is nonmagnetic or magnetic and whether it is described using the drude- or plasma - model approaches . however , for nonmagnetic metals described by the plasma model and for magnetic metals , a severe dependence on the chosen theoretical description of graphene remains even at high temperature . in all cases the analytic asymptotic expressions for the free energy at high temperature are obtained and found in a very good agreement with the results of numerical computations .

we investigate the thermal casimir interaction of a suspended graphene described by the dirac model with a plate made of dielectric or metallic materials . the reflection coefficients on graphene expressed in terms of a temperature - dependent polarization tensor are used . we demonstrate that for a graphene with nonzero mass gap parameter the casimir free energy remains nearly constant ( and the thermal correction negligibly small ) over some temperature interval . for the interaction of graphene with metallic plate , the free energy is nearly the same , irrespective of whether the metal is nonmagnetic or magnetic and whether it is described using the drude- or plasma - model approaches . the free energy computed using the dirac model was compared with that computed using the hydrodynamic model of graphene and big differences accessible for experimental observation have been found . for dielectric and nonmagnetic metallic plates described by the drude model these differences vanish with increasing temperature ( separation ) . however , for nonmagnetic metals described by the plasma model and for magnetic metals , a severe dependence on the chosen theoretical description of graphene remains even at high temperature . in all cases the analytic asymptotic expressions for the free energy at high temperature are obtained and found in a very good agreement with the results of numerical computations .

1509.04637

i

quantum markovian master equations are the simplest but also the most used cases of study for the dynamics of open quantum systems . the concept of open systems plays an important role since perfect isolation in the quantum realm and access to all degrees of freedom is not possible . the main source of inspiration was the theory of lasers where models describing the interaction of a central subsystem weakly coupled to an uncontrollable environment were studied . in the last two decades there has been great interest in the study of composite quantum systems in order to create entanglement between them @xcite with the ultimate aim to realize quantum information procedures @xcite . however , there is always an environment causing decoherence which is also the bottleneck to realize highly efficient quantum information protocols . therefore the theory of open quantum systems was frequently applied to various models @xcite . there is a subclass of models which can be decomposed into many interacting parts which in turn are coupled to independent environments . the best example is the case of two - level atoms interacting with a single mode of the radiation field and coupled to independent reservoirs , like the model of the many - atom laser @xcite or the one - atom maser @xcite . the time evolution of the composite system is derived from a microscopic model or is assembled on the ground of phenomenological considerations from equations which describe independently the parts . the latter case usually assumes a low coupling strength between the two parties which allows a separate description of dissipative effects . in both cases the possible treatments of environments consist in markovian and non - markovian approaches @xcite . obtaining the full solution to the dynamical equation is a very complicated task even with a markovian approach @xcite and sometimes one has to be satisfied by identifying the steady state @xcite or its symmetry properties @xcite . in general , the role of the interaction in a composed system was studied typically for two coupled harmonic oscillators @xcite and for two interacting identical atoms @xcite . in this paper , we focus on the case when two independent quantum systems @xmath0 and @xmath1 are subject to markovian master equations and their interaction is studied through an equation which is obtained by adding the two master equations to a hamiltonian interaction . for physical systems , this consideration usually implies that the interaction strength between @xmath0 and @xmath1 has to be the smallest parameter in the system . we concentrate on a special class of interaction hamiltonians that cause dephasing on system @xmath0 and lead to a generator ( liouvillian ) of the complete system that commutes with the liouvillian of system @xmath0 s master equation . the motivating example is the optomechanical coupling between a single - mode electromagnetic field and a small mechanical oscillator in the presence of independent decoherence mechanisms @xcite . it will be demonstrated that the considered class of interaction hamiltonians leads to an invariant steady state of system @xmath0 , i.e. , tracing out system @xmath1 in the steady state of the composite system one always obtains the same steady state of system @xmath0 which is independent of the interaction hamiltonian . in contrast , the steady state of system @xmath1 may depend on the interaction . in the case of finite dimensional systems , theorems of linear algebra can be employed to prove the statement . however , when dealing with infinite dimensional systems a different and more sophisticated method is required . therefore , the proof of the invariant steady state is based on the properties of quantum dynamical semigroups where we employ the trotter product formula and identify the growth bounds of the master equations . while the proof of our statement is rather general we will explicitly show it in some simple models . the steady state of system @xmath1 does not have any particular property and its solution is model dependent . therefore in our examples we study the steady state of system @xmath1 by analyzing its average excitation . our work presents a general approach towards composite systems governed by independent markovian master equations . this paper is organized as follows . in sec . [ ex1 ] we discuss the motivation of our analysis . in sec . [ ststa ] we show the general statement about the steady state . in sec . [ ex ] , we apply these findings to three different systems : two interacting spins , a spin interacting with a harmonic oscillator and two coupled harmonic oscillators . a discussion about our findings is summarized up in sec . [ remarks ] . in appendix [ appendix0 ] we briefly discuss the liouvillians of the markovian master equations involving some technical problems regarding infinite dimensional hilbert spaces . in appendix [ appendix ] we analyse the form of the equilibrium state of a damped harmonic oscillator in the number state representation .

we investigate two interacting open quantum systems whose time evolutions are governed by markovian master equations . we show a class of coupled systems whose interaction leaves invariant the steady state of one of the systems , i.e. , only one of the reduced steady states is sensitive to the interactions .

we investigate two interacting open quantum systems whose time evolutions are governed by markovian master equations . we show a class of coupled systems whose interaction leaves invariant the steady state of one of the systems , i.e. , only one of the reduced steady states is sensitive to the interactions . a detailed proof with the help of the trotter product formula is presented . we apply this general statement to a few models , one of which is the optomechanical coupling model where an optical cavity is coupled to a small mechanical oscillator .

1502.05428

i

although the source - channel separation architecture is asymptotically optimal in the point - to - point communication setting @xcite as well as several classes of multiuser communication settings ( see _ e.g. , _ @xcite and references therein ) , uncoded schemes have several particularly attractive properties . firstly , they have very simple encoders and decoders ; secondly , they belong to the so - called zero - delay codes , which can avoid the long delay required to approach the asymptotic performance in the separation - based schemes ; lastly , they are in fact optimal in some settings , while the separation - based schemes are not ( see _ e.g. _ , @xcite ) . it was shown in @xcite that uncoded schemes are optimal when certain matching conditions involving the source probability distribution , the channel transition probability distribution , the channel cost function and the distortion measure function are satisfied . though the focus in @xcite was mainly on the point - to - point setting , recent results @xcite suggest that the concept of matching indeed carries over to the multiuser case . in fact , in multiuser settings , matching may occur naturally when the distortion measure , the channel cost function and source distribution are all fixed , and the channel parameters , which represent physically meaningful quantities , satisfy certain conditions . in this work , we consider such matching , particularly , when the sources and the channels are gaussian , the channel constraints are on the expected average signal power , the distortion measure is the mean squared error ( mse ) , and only the channels parameters , such as the channel amplification factors and the additive noise powers , are allowed to vary . in this context , of interest is whether for a fixed source and fixed coding parameters , the distortion vector such induced is on the boundary of the achievable distortion region ( and thus optimal ) . more specifically , we seek to answer the following questions : * is there a set of ( explicitly ) computable conditions that can be used to certify a fixed uncoded scheme to be optimal for a given source and channel pair ? * if so , is there a non - trivial set of channels that satisfy such conditions for a given source and uncoded scheme pair ? we shall refer to this kind of channels as `` matched channels '' ; a dual question is to ask for `` matched sources '' , however in the context of problems considered here , the dual question is notationally more involved , and thus we choose to investigate the problems from the perspective of `` matched channels '' . one can also ask for `` matched distortion measures '' , similarly as the approach taken in @xcite , however in the gaussian setting we consider here , fixing the mse distortion is practically more important and well - motivated . the set of matched channels should be distinguished from the complete set of channels for which the given uncoded scheme is optimal . the former may be a strict subset of the latter , since the former may be only sufficient for an uncoded scheme to be optimal , which usually depends on the specific outer bounding technique employed . characterizing the latter region is naturally more difficult than answering the questions we posed above . the two questions posed above are in essence the two facets of the same question . since we only provide conditions for matching , or in other words , sufficient conditions for the scheme to be optimal , the set of matched channels may in fact be empty . a trivial condition to answer the first question is simply an impossible one such that we would never be able to certify a channel to be matched . thus the second question is important , and we show indeed for the two problems considered here , there are non - trivial channels that match the source and the uncoded scheme . traditionally , research in information theory asks for characterization of certain achievable region , for which we first derive an expression for an outer bound , and derive an expression for an inner bound , and then make comparison of them . this approach can be challenging because it usually involves optimization over a set of parameters , and solving such an optimization problem explicitly can be difficult . it is not clear whether the obstacle mainly stems from the intractable nature of the underlying communication problem , or it is mainly caused by the embedded optimization problem . the aforementioned difficulty motivates the formulation of the first question , which is a decision problem instead of an optimization problem . an analogy of this situation can be found in computer science algorithm research , where instead of asking whether an optimization problem can be solved in polynomial time , the alternative question is asked whether a decision ( _ e.g. _ , regarding a solution is above a threshold ) can be made in polynomial time . our problem formulation naturally leads to a different approach in the investigation . instead of focusing on comparison of the inner bounds and outer bounds using their expressions , we focus on the necessary conditions that the outer bound becomes tight , _ i.e. , _ the conditions when the information inequalities hold with strict equality . with fixed source and fixed coding parameters , the coding vector can be substituted into the conditions , and the necessary and sufficient conditions for such equality can be derived . the outer bounds naturally provide certain `` decoupled '' conditions , which significantly simplifies the overall task . though this approach may have inherently been used by many researchers in the past , its effectiveness becomes particularly evident in our investigation of uncoded schemes in the joint source channel communication setting . in the rest of the paper , we focus specifically on two joint source channel coding problems using the approach outlined above . the first problem is to send correlated gaussian sources on a gaussian broadcast channel where each receiver is interested in reconstructing only one source component ( or equivalently one specific linear function of the source ) under the mse distortion measure . the second problem is to send vector gaussian sources on a gaussian multiple - access channel , where each transmitter observes a noisy combination of the source , _ i.e. , _ a case of the vector ceo problem , and the receiver wishes to reconstruct the source components ( or equivalently linear functions of the source components ) under the mse distortion measure . general conditions for matching are derived , which either include or generalize well - known existing results on the optimality of uncoded schemes in the multiuser setting . particularly notable are the following cases : * the first problem generalizes the two - user case considered in @xcite and @xcite to the @xmath0-user case , for which we show that the uncoded scheme is optimal for a large set of sources and channels ; our results reveal that uncoded scheme can still be optimal when some source components are negatively correlated . * the results on the second problem includes as specials cases the symmetric scalar gaussian ceo problem @xcite , the problem of sending bivariate gaussian sources on a gaussian multiple - access channel @xcite , and sending remote ( noisy ) bivariate gaussians on a gaussian multiple - access channel @xcite . our results reveal that in addition to the symmetric case considered in @xcite , uncoded scheme is also optimal when the sensor observation quality is proportional to the channel quality . these results also allow the sensor observations to have more general correlation structure and the observations to be noisy , thus extending the results in@xcite and @xcite . when viewed from the perspective of computation , our result also provides new characterizations for the problem of computing linear functions of gaussian random variables on the gaussian multiple - access channels considered in @xcite and @xcite . notationally , we write for a source @xmath1 at time @xmath2 as @xmath3 $ ] , and a length-@xmath4 vector as @xmath5 . for a set of coefficients @xmath6 , we sometimes write it in a ( column ) vector form as @xmath7 . for a real matrix @xmath8 , we write its transpose as @xmath9 . the positive semidefinite order is denoted as @xmath10 .

we investigate whether uncoded schemes are optimal for gaussian sources on multiuser gaussian channels . particularly , we consider two problems : the first is to send correlated gaussian sources on a gaussian broadcast channel where each receiver is interested in reconstructing only one source component ( or one specific linear function of the sources ) under the mean squared error distortion measure ; the second is to send vector gaussian sources on a gaussian multiple - access channel , where each transmitter observes a noisy combination of the source , and the receiver wishes to reconstruct the individual source components ( or individual linear functions ) under the mean squared error distortion measure . we ask the question whether and how a match can be effectively determined .

we investigate whether uncoded schemes are optimal for gaussian sources on multiuser gaussian channels . particularly , we consider two problems : the first is to send correlated gaussian sources on a gaussian broadcast channel where each receiver is interested in reconstructing only one source component ( or one specific linear function of the sources ) under the mean squared error distortion measure ; the second is to send vector gaussian sources on a gaussian multiple - access channel , where each transmitter observes a noisy combination of the source , and the receiver wishes to reconstruct the individual source components ( or individual linear functions ) under the mean squared error distortion measure . it is shown that when the channel parameters match certain general conditions , the induced distortion tuples are on the boundary of the achievable distortion region , and thus optimal . instead of following the conventional approach of attempting to characterize the achievable distortion region , we ask the question whether and how a match can be effectively determined . this decision problem formulation helps to circumvent the difficult optimization problem often embedded in region characterization problems , and also leads us to focus on the critical conditions in the outer bounds that make the inequalities become equalities , which effectively decouples the overall problem into several simpler sub - problems . = 0.2 cm

1205.5920

i

communication networks are presenting ever - increasing challenges in a wide range of applications , and there is great interest in inferential methods for exploiting the information they contain . a common source of such data is a corpus of time - stamped messages such as e - mails or sms ( short message service ) . such messaging data is often useful for inferring a social structure of the community that generates the data . in particular , messaging data is an asset to anyone who would like to cluster actors according to their _ similarity_. a practitioner is often privy to messaging data in a _ streaming _ fashion , where the word _ streaming _ describes a practical limitation , as the practitioner might be privy only to the incoming data in a fixed summarized form without any possibility to retrieve past information . it is in the practitioner s interest to transform the summarized data so that the transformed data is appropriate for detecting _ emerging _ social trends in the source community . we mathematically model such streaming data as a collection of tuples of the form @xmath0 of time and actors , where @xmath1 and @xmath2 represent actors exchanging the @xmath3-th message and @xmath4 represents the occurrence time of the @xmath3-th message . there are many models suitable for dealing with such data . the most notable are the cox hazard model , the doubly stochastic process ( also known as the cox process ) , and the self - exciting process ( although self - exciting processes are sometimes considered as special cases of the cox hazard model ) . for references on these topics , see @xcite , @xcite and @xcite . all three models are related to each other ; however , the distinctions are crucial to statistical inference as they stem from different assumptions on information available for ( online ) inference . to transform @xmath5 data to a data representation more suitable for clustering actors , we model @xmath5 as a ( multivariate ) doubly stochastic process , and develop a method for embedding @xmath5 as a stochastic process taking values in @xmath6 for some suitably chosen @xmath7 .

we model messaging activities as a hierarchical doubly stochastic point process with three main levels , and develop an iterative algorithm for inferring actors relative latent positions from a stream of messaging activity data . = 1 social network ; multiple doubly stochastic processes ; classification ; clustering 62m0 , 60g35 , 60g55

we model messaging activities as a hierarchical doubly stochastic point process with three main levels , and develop an iterative algorithm for inferring actors relative latent positions from a stream of messaging activity data . each of the message - exchanging actors is modeled as a process in a latent space . the actors latent positions are assumed to be influenced by the distribution of a much larger population over the latent space . each actor s movement in the latent space is modeled as being governed by two parameters that we call confidence and visibility , in addition to dependence on the population distribution . the messaging frequency between a pair of actors is assumed to be inversely proportional to the distance between their latent positions . our inference algorithm is based on a projection approach to an online filtering problem . the algorithm associates each actor with a probability density - valued process , and each probability density is assumed to be a mixture of basis functions . for efficient numerical experiments , we further develop our algorithm for the case where the basis functions are obtained by translating and scaling a standard gaussian density . = 1 social network ; multiple doubly stochastic processes ; classification ; clustering 62m0 , 60g35 , 60g55

1205.5920

l

for statistical inference when there is information available beyond @xmath5 , the cox - proportional hazard model is a natural choice . in @xcite and @xcite , for instance , instantaneous intensity of messaging activities between each pair of actors is assumed to be a function of , in the language of generalized linear model theory , known covariates with unknown regression parameters . more specifically , in @xcite , the authors consider a model where @xmath8 with @xmath9 and @xmath10 representing independent counting processes , e.g. , @xmath9 are bernoulli random variables and @xmath10 are random variables from the exponential family . on the other hand , in @xcite , a cox multiplicative model was considered where @xmath11 . the model in @xcite posits that actor @xmath12 interacts with actor @xmath13 at a baseline rate @xmath14 modulated by the pair s covariate @xmath15 whose value at time @xmath16 is known and @xmath17 is a common parameter for all pairs . in @xcite , it is shown under some mild conditions that one can estimate the global parameter @xmath17 consistently . in @xcite , the intensity is modeled for _ adversarial _ interaction between _ macro _ level groups , and a problem of nominating unknown participants in an event as a missing data problem is entertained using a self - exciting point process model . in particular , while no explicit intensity between a pair of actors ( gang members ) is modeled , the event intensity between a pair of groups ( gangs ) is modeled , and the spatio - temporal model s chosen intensity process is self - exciting in the sense that each event can affect the intensity process . when data @xmath5 is the only information at hand , a common approach is to construct a time series of ( multi-)graphs to model association among actors . for such an approach , a simple method to obtain a time series of graphs from @xmath18 is to `` pairwise threshold '' along a sequence of non - overlapping time intervals . that is , given an interval , for each pair of actors @xmath12 and @xmath13 , an edge between vertex @xmath12 and vertex @xmath13 is formed if the number of messaging events between them during the interval exceeds a certain threshold . this is the approach taken in @xcite , @xcite and @xcite , to mention just a few examples . the resulting graph representation is often thought to capture the structure of some underlying social dynamics . however , recent empirical research , e.g. , @xcite , has begun to challenge this approach by noting that changing the thresholding parameter can produce dramatically different graphs . another useful approach when @xmath5 is the only information available is to use a doubly stochastic process model in which count processes are driven by latent factor processes . this is the approach taken explicitly in @xcite and @xcite , and this is also done implicitly in @xcite . in @xcite and @xcite interactions between actors are specified by proximity in their latent positions ; the closer two actors are to each other in their latent configuration , the more likely they exchange messages . using our model , we consider a problem of clustering actors `` online '' by studying their messaging activities . this allows us a more geometric approach afforded by embedding @xmath19 data to an @xmath20 representation for some fixed dimension @xmath21 . in this paper , we propose a useful mathematical formulation of the problem as a filtering problem based on both a multivariate point process observation and a population latent position distribution .

each of the message - exchanging actors is modeled as a process in a latent space . each actor s movement in the latent space is modeled as being governed by two parameters that we call confidence and visibility , in addition to dependence on the population distribution . the messaging frequency between a pair of actors our inference algorithm is based on a projection approach to an online filtering problem . the algorithm associates each actor with a probability density - valued process , and each probability density is assumed to be a mixture of basis functions . for efficient numerical experiments , we further develop our algorithm for the case where the basis functions are obtained by translating and scaling a standard gaussian density .

we model messaging activities as a hierarchical doubly stochastic point process with three main levels , and develop an iterative algorithm for inferring actors relative latent positions from a stream of messaging activity data . each of the message - exchanging actors is modeled as a process in a latent space . the actors latent positions are assumed to be influenced by the distribution of a much larger population over the latent space . each actor s movement in the latent space is modeled as being governed by two parameters that we call confidence and visibility , in addition to dependence on the population distribution . the messaging frequency between a pair of actors is assumed to be inversely proportional to the distance between their latent positions . our inference algorithm is based on a projection approach to an online filtering problem . the algorithm associates each actor with a probability density - valued process , and each probability density is assumed to be a mixture of basis functions . for efficient numerical experiments , we further develop our algorithm for the case where the basis functions are obtained by translating and scaling a standard gaussian density . = 1 social network ; multiple doubly stochastic processes ; classification ; clustering 62m0 , 60g35 , 60g55

astro-ph0411655

i

of the sample of stars observed from the cfht , those with planets ( with the exception of 51 peg ) show significant night - to - night variations in their ca ii h and k reversals . @xmath5 ceti and the sun , which have no close planets , remained very steady throughout each of the four observing runs . hd 179949 and @xmath1 and exhibited repeated orbital phase - dependent activity with enhanced emission leading the sub - planetary point by 0.17 and 0.47 in orbital phase , respectively . both systems are consistent with a magnetic heating scenario and may be the first glimpse at the magnetospheres of extrasolar planets . the phase - lead or lag of the peak emission relative to the sub - planetary longitude can provide information on the field geometries and the nature of the effect such as tidal friction , magnetic drag or reconnection with off - center magnetic fields , including a parker - spiral type scenario . @xmath5 boo and hd 209458 also exhibited night - to - night variations that could not exclusively be due to stellar rotation . if @xmath5 boo is indeed tidally locked by its hot jupiter , there is no orbital energy available to generate the alfvn modes efficiently as the stellar fields sweep across the planet due to the slow relative azimuthal motion . we measured the excess absolute flux released in the enhanced chromospheric emission of hd 179949 to be the same order of magnitude as a typical solar flare , @xmath8 10@xmath47 erg s@xmath20 or 1.5@xmath2610@xmath48 ergs s@xmath20 @xmath49 . this implies that flare - like activity triggered by the interaction of a star with its hot jupiter may be an important energy source in the stellar outer atmosphere . this offers a mechanism for short - term chromospheric activity . the h & k emission of @xmath0 ceti , an active star with no confirmed planet , was clearly modulated by the star s 9.3-d rotation . similarly , hd 73256 displayed rotational modulation with its 14-d period . in these two cases , the chromospheric emission increases by @xmath6 6% ( relative to the normalization level at 1/3 of the continuum ) . any planet - induced heating at the level of 1 @xmath19 2% could have been diluted by the dominating hotspot on the stellar surface . neither the @xmath27rvs nor the ca ii periodicity exclude the possibility of a sub - stellar companion in a tight orbit around @xmath0 ceti . apart from the cyclical component for four of the stars , short - term chromospheric activity appears weakly dependent on the mean k - line reversal intensities for the sample of 13 stars . also , a suggestive correlation exists with @xmath2sin@xmath3 and thus with the hot jupiter s magnetic field strength . because of their small separation ( @xmath4 0.1 au ) , many of the hot jupiters lie within the alfvn radius of their host stars which allows a direct magnetic interaction with the stellar surface . additional ca ii observations are crucial to confirm the stability of the magnetic interaction as well as to establish better phase coverage . observations on timescales of a few years will begin to characterize the long - term activity of our program stars and allow us to see correlations between intrinsic ca ii emission and night - to - night activity more clearly . this work opens up the possibility of characterizing planet - star interactions with implications for extrasolar planet magnetic fields and the energy contribution to stellar atmospheres . a next step in understanding planet - star interactions is to map the activity as a function of stellar atmospheric height . above the chromosphere lies the thin transition region ( tr ) , where the temperature increases steeply as density and pressure drop , and the corona , which can extend out to several stellar radii . and since the magnetic field drops off as @xmath82 ( where @xmath127 ) , these layers facilitate a stronger interaction with the planet . their fuv and x - ray emissions will be extremely important diagnostics . one indication that the heating is from the outside in is if the increase in emission occurs slightly earlier in phase than in ca ii . moreover , the relative strengths of the different emission lines will tell us where most of the energy is dissipated . the energy sum will point out if there are any discrepancies with the theorized energy budget . orbital phase - dependent variability at these heights will constrain further the nature , form and strength of the interaction as well as specify non - thermal radiative processes in these hot layers of gas . we are grateful to marek wolf and petr harmanec for their photometric observations of hd 179949 made at the south african astronomical observatory ( saao ) . we thank geoff bryden , peng - fei chen , gary glatzmaier , gordon i. ogilvie , and ethan t. vishniac for useful communications regarding section [ theory ] . research funding from the canadian natural sciences and engineering research council ( g.a.h.w . & e.s . ) and the national research council of canada ( d.a.b . ) is gratefully acknowledged . we are indebted to the cfht staff for their care in setting up the cafe fiber feed and the gecko spectrograph , as well as to the staff at eso s vlt for their telescope and instrument support and the real - time data - reduction pipeline . also , we appreciate the helpful comments and suggestions from the referee , steve saar . mazeh , t. , naef , d. , torres , g. , latham , d.w . , mayor , m. , beuzit , j .- l . , brown , t.m . , buchhave , l. , burnet , m. , carney , b.w . , charbonneau , d. , drukier , g. , laird , j.b . , pepe , f. , perrier , c. , queloz , d. , santos , n.c . , sivan , j .- p . , udry , s. , zucker , s. , 2000 , , 532 , l55 saar , s.h . , shkolnik , e. , cuntz , m. , 2003 , in iau symp . 219 , stars as suns : activity , evolution and planets , international astronomical union . symposium no . 219 , held 21 - 25 july , in sydney , australia , meeting abstract walker , g.a.h . , matthews , j.m . , kuschnig , r. , johnson , r. , rucinski , s. , pazder , j. , burley , g. , walker , a. , skaret , k. , zee , r. , grocott , s. , carroll , k. , sinclair , p. , sturgeon , d. , harron , j. , 2003b , , 115 , 1023

four stars display short - term ( days ) cyclical activity . for two , short - term chromospheric activity appears weakly dependent on the mean k - line reversal intensities for the sample of 13 stars . also , a suggestive correlation exists between this activity and thesin of the star s hot jupiter . because of their small separation ( 0.1 au ) , many of the hot jupiters lie within the alfvn radius of their host stars which allows a direct magnetic interaction with the stellar surface . boo . this work opens up the possibility of characterizing planet - star interactions , with implications for extrasolar planet magnetic fields and the energy contribution to stellar atmospheres .

we monitored the chromospheric activity in the ca ii h & k lines of 13 solar - type stars ( including the sun ) ; 8 of them over three years at the cfht and 5 in a single run at the vlt . ten of the 13 targets have close planetary companions . all of the stars observed at the cfht show long - term ( months to years ) changes in h & k intensity levels . four stars display short - term ( days ) cyclical activity . for two , hd 73256 and ceti , the activity is likely associated with an active region rotating with the star , however , the flaring in excess of the rotational modulation may be associated with a hot jupiter . a planetary companion remains a possibility for ceti . for the other two , hd 179949 and and , the cyclic variation is synchronized to the hot jupiter s orbit . for both stars this synchronicity with the orbit is clearly seen in two out of three epochs . the effect is only marginal in the third epoch at which the seasonal level of chromospheric activity had changed for both stars . short - term chromospheric activity appears weakly dependent on the mean k - line reversal intensities for the sample of 13 stars . also , a suggestive correlation exists between this activity and thesin of the star s hot jupiter . because of their small separation ( 0.1 au ) , many of the hot jupiters lie within the alfvn radius of their host stars which allows a direct magnetic interaction with the stellar surface . we discuss the conditions under which a planet s magnetic field might induce activity on the stellar surface and why no such effect was seen for the prime candidate , boo . this work opens up the possibility of characterizing planet - star interactions , with implications for extrasolar planet magnetic fields and the energy contribution to stellar atmospheres .

0903.0569

i

factorization theorems are fundamental to modern calculations in qcd of the amplitudes for hard - scattering exclusive hadronic processes . they allow one to separate contributions to the amplitudes that involve states of high virtuality from those that involve states of low virtuality . the former , short - distance contributions can , by virtue of asymptotic freedom , be calculated in perturbation theory , while the latter , long - distance contributions are parametrized in terms of inherently nonperturbative matrix elements of qcd operators in hadronic states . states of low virtuality can arise from the emission of a soft gluon , whose four - momentum components are all small , or from the emission of a collinear gluon , whose four - momentum is nearly parallel to the four - momentum of a gluon or light quark . in some discussions of factorization that employ soft - collinear effective theory ( scet ) @xcite or diagrammatic methods @xcite , it is assumed that gluons can have no transverse momentum components that are smaller than the qcd scale @xmath1 . that is , gluons can have hard momentum , in which all components are of order the hard - scattering scale @xmath2 , soft momentum , in which all components are of order @xmath3 , or collinear momentum , in which the transverse components are of order @xmath3 and the energy and longitudinal spatial component are much larger than @xmath1 ( usually taken to be of order @xmath2 ) . this assumption is appropriate to the discussion of physical hadrons , in which confinement provides a nonperturbative ir cutoff of order @xmath1 . however , in perturbative matching calculations of short - distance coefficients , one usually takes the external quark and gluon states to be on their mass shells , and , in this situation , soft and collinear gluons of arbitrarily low energy can be emitted . in order to establish the consistency of such calculations , one must prove , to all orders in perturbation theory , that these soft and collinear gluons factor from the hard - scattering process and that the factorized form is identical to the conventional one that is obtained in the presence of an infrared cutoff of order @xmath3 . or greater , then the short - distance coefficients are independent of all infrared modes , even in perturbative calculations in which modes with scales below @xmath3 are present . this was shown to be the case in a one - loop example . however , no general , all - orders proof of that assertion was given . ] in the absence of such a proof , one would have no guarantee in the matching calculation that low - virtuality soft and collinear contributions either cancel or can be absorbed entirely into the standard nonperturbative functions ( distribution functions in inclusive processes and distribution amplitudes in exclusive processes ) . at the one - loop level , gluons of arbitrarily low energy can be treated along with higher - energy soft and collinear gluons , and the conventional proofs of factorization apply . however , as we shall see , the proof of factorization of low - energy gluons becomes more complicated beyond one loop . in multiloop integrals , in the on - shell case , one finds contributions at leading power in the hard - scattering momentum in which collinear gluons of low energy couple to soft gluons . our goal is to construct a proof of factorization that takes this possibility into account . to our knowledge , the existing discussions of factorization , either in the context of scet or diagrammatic methods , have not addressed this possibility . in on - shell perturbative calculations in scet , gluon transverse momenta extend to zero . hence , the possibility of low - energy gluons with momenta collinear to one of the external particles arises . at one - loop level , the soft and collinear contributions can be separated through the use of an additional cutoff @xcite . however , as we have already mentioned , at two - loop level and higher , a low - energy collinear gluon can attach to a soft gluon . the scet action is formulated so that soft gluons can be decoupled from collinear gluons through a field redefinition , but there is no corresponding provision to decouple collinear gluons from soft gluons . therefore , it seems that , in scet , low - energy collinear gluons would be treated most straightforwardly as part of the soft ( or ultrasoft ) contribution . this results in a factorized form in which the soft function contains gluons with both soft and collinear momenta and , hence , contains both soft and collinear divergences . alternatively , one can consider a factorized form in which gluons with collinear momenta are factored completely from the soft function , so that they reside only in jet functions that are associated with the initial- or final - state hadrons . such an alternative factorized form , in which the soft function is free of collinear divergences , has been discussed in the context of factorization for the drell - yan process in refs . @xcite , although the details of the factorization of gluons with collinear momenta from the soft function were not given . this alternative factorized form has also been discussed in connection with resummation of logarithms in , for example , refs . furthermore , it has been discussed in an axial gauge in the context of on - shell quark scattering @xcite . axial gauges are somewhat problematic , in that they introduce unphysical singularities into gluon and ghost propagators . such singularities could potentially spoil contour - deformation arguments that are used to ascertain the leading regions of integration in feynman diagrams @xcite . for this reason , we believe that it is important to construct a proof of factorization in a covariant gauge , such as the feynman gauge , which we employ in the present paper . a factorized form in which the soft function contains no gluons with collinear momenta has several useful features . one is that contributions in which there are two logarithms per loop ( one collinear and one soft ) reside entirely in the jet functions , which have a diagonal color structure , rather than in the soft function , which has a more complicated color structure . here we focus on a feature that is crucial for factorization proofs : a factorized form in which the soft function contains no collinear modes allows one to establish a cancellation of the soft function when it connects to a color - singlet hadron . as we shall explain below , if the soft function contains gluons with collinear momenta , then the cancellation of the soft function fails at leading order in the large momentum scale . in this paper , we outline the proof of factorization at leading order in the hard - scattering momentum for the case of on - shell external partons . for concreteness , we discuss the example of the exclusive production of two light mesons in @xmath0 annihilation . in an intermediate step , the factorized form that we obtain contains a soft function that is free of collinear divergences . this allows us to demonstrate the cancellation of the soft function at leading order in the large momentum scale . our proof makes use of standard all - orders diagrammatic methods for proving factorization @xcite . we find that the factorization of gluons of arbitrarily low energy can be dealt with conveniently by focusing on the factorization of contributions to loop integrals from singular regions , _ i.e. _ , regions that contain the soft and collinear singularities . such singular regions are discussed in refs . @xcite . however , the coupling of low - energy collinear gluons to soft gluons is not discussed in those papers . the remainder of this paper is organized as follows . in sec . [ sec : model - amp ] we describe the model that we use for the production amplitude . section [ sec : leading - regions ] contains a heuristic discussion of the regions of loop momenta that give leading contributions . this discussion is aimed at making contact with previous work on factorization and also sets the stage for a more precise discussion of the singular regions of loop momenta . in sec . [ sec : topology ] , we discuss the diagrammatic topology of the leading contributions and also the topology of the soft and collinear singular contributions . we treat the collinear and soft contributions by making use of collinear and soft approximations that are valid in the singular regions . these are discussed in sec . [ sec : decoupling ] , along with the decoupling relations for the collinear and soft singular contributions . in sec . [ sec : factorization ] , we outline the factorization of the collinear and soft singularities and describe how one arrives at the standard factorized form for the production amplitude . we also outline the proof of factorization in the case in which the relative momentum between the quark and the antiquark in a meson is taken to be nonzero . here , we discuss the difficulty that arises in the cancellation of the soft function if the soft function contains gluons with collinear momenta . finally , in sec . [ sec : summary ] , we summarize our results .

we outline a proof of factorization in exclusive processes , taking into account the presence of soft and collinear modes of arbitrarily low energy , which arise when the external lines of the process are taken on shell . specifically , we examine the process of annihilation through a virtual photon into two light mesons . in an intermediate step , we establish a factorized form that contains a soft function that is free of collinear divergences . in contrast , in soft - collinear effective theory , the low - energy collinear modes factor most straightforwardly into the soft function .

we outline a proof of factorization in exclusive processes , taking into account the presence of soft and collinear modes of arbitrarily low energy , which arise when the external lines of the process are taken on shell . specifically , we examine the process of annihilation through a virtual photon into two light mesons . in an intermediate step , we establish a factorized form that contains a soft function that is free of collinear divergences . in contrast , in soft - collinear effective theory , the low - energy collinear modes factor most straightforwardly into the soft function . we point out that the cancellation of the soft function , which relies on the color - singlet nature of the external hadrons , fails when the soft function contains low - energy collinear modes .

1212.5606

i

with what seems to be the recent discovery of the higgs boson @xcite , the high energy physics enters into the solitude of a path that no one knows where or how it may found new physics ( np ) . although a light higgs requires either , fine - tuning , or np at the tev scale , the experimental results do not show any hint of new phenomena insofar . as a matter of fact , _ natural _ supersymmetry , which is one of the most popular theories to avoid fine - tuning and to simultaneously explain many other phenomena , is being highly constrained by direct searches at the lhc @xcite . from a general theoretical point of view , one may expect to have np effects in the detailed study of the heavier particles properties . in particular , the top quark is the heaviest known particle and its properties have not been explored in depth insofar . in fact , last years results from tevatron @xcite seemed to point to np in the top forward - backward asymmetry . however , recent results from the top charge asymmetry at lhc @xcite , have contradicted most of the np proposals except for very few models @xcite that have survived . regardless of these recent results in top physics , in this article we consider the inclusive @xmath7 process where we study the @xmath8 invariant mass ( @xmath9 ) spectrum as a sensitive observable to np resonant phenomena . this is due to a potential enhancement in the coupling of the top quark to the np . in this work , we address the question of how to increase the sensitivity of this observable in the case of np that couples to quarks and not to gluons . the reason for this study is that at the lhc most ( @xmath10 at @xmath11 tev and increasing with energy ) of the @xmath8 events have a gluon in the initial state partons and , therefore , a possible np as the stated above would be per - se diluted just because of the initial state partons of the event . for the sake of brevity , from this point forward we call gluon - fusion any event with at least one gluon in the initial state . the goal of this article is to propose kinematic cuts which enrich the quark - annihilation fraction ( @xmath12 ) of a selected @xmath8 sample in order to increase the sensitivity to the stated np in the @xmath9-spectrum . moreover , in light of the upcoming experimental results , we focus our work to the @xmath13 tev region of energy . this range of energies has two special features which determine the results in this work : _ i ) _ we propose to use as one of the variables to discriminate quark - annihilation events , the center of mass scattering angle , which is useful for this purpose at high @xmath9 ; and _ ii ) _ the lack of statistics at high @xmath9 requires a special selection criteria that with small cuts makes considerable increases in the sensitivity . this latter is in contrast to the low energy regime , where strong cuts that yield a very large increase in the sensitivity are sought . the search for kinematic cuts that increase @xmath12 in a given @xmath8 sample has been studied in the last years @xcite mainly to increase the sensitivity in the top charge - asymmetry at the lhc and very few in the @xmath9-spectrum @xcite . these articles deal mainly with two different features in the production mechanisms that allow to distinguish @xmath14 production in @xmath7 . the first one is that valence quarks inside the colliding protons tend to have larger fraction of the proton momentum than gluons and anti - quarks . therefore , top pairs produced through quark - annihilation tend to be boosted along the pipe line . this characteristic can be measured through the kinematic variable = , [ beta ] which ranges from @xmath15 for not boosted pairs to @xmath16 for maximum boosted pairs . notice for future purposes that the origin of this feature is in the proton parton distribution function ( pdf ) . the second feature which allows to isolate top pairs produced through quark - annihilation is that initial state gluons tend to produce more initial state radiation ( isr ) than quarks . this is an effect due to a larger numeric factor in the three gluon vertex in the qcd lagrangian . this characteristic can be measured through the transverse momentum of the top pair , p_t=| p_t(t ) + p_t(|t ) | . [ pt ] the larger is @xmath3 , the more probable is to have a gluon in the initial state . notice that , in this case , the origin of this feature is pure qcd and is independent not only from the pdf , but also from the dynamics in the @xmath8 production process . the usage of these two variables to increase the sensitivity to np in the @xmath9-spectrum has been exploited in refs . @xcite . there is a third variable which may serve to distinguish quark - annihilation processes . this is the center of mass scattering angle ( @xmath4 ) of the top quark direction relative to the right moving parton . this variable has been previously studied in refs . since , as we show in the article , to take profit of this variable requires large @xmath9 , we use it to study the upcoming experimental results where the @xmath9 region above @xmath16 tev will be better analyzed . this variable is related to the dynamics of the @xmath17 process and the spin of the particles . the key feature in using the angular distribution is that for large @xmath9 the quark - annihilation processes have a smooth angular distribution , whereas gluon - fusion processes accumulate most of the events in the forward @xmath18 region . or , to be more precise , the @xmath19-channel @xmath20 amplitude is the one that peaks the production in the forward region for relativistic tops . therefore , the angular distribution may also be understood as a discriminator of @xmath21- from @xmath19-channel contributions , as in dijet resonance searches @xcite . the aim of this work is to analyze simultaneously cuts in all three variables ( @xmath22 and @xmath4 ) to enhance the sensitivity to resonant np in the @xmath9-spectrum by increasing @xmath12 . notice that , although all three variables have different origins , they have some degree of indirect correlation through the pdf s . in any case due to their different origin none of them can be expressed as a function of the other two . the price to pay for increasing @xmath12 is to reduce the fraction of the original sample ( @xmath23 ) that is selected for the analysis . this reduction , which always yields an increase in the statistical uncertainty , may not worth the selection . the critical point up to where it is convenient to cut the sample depends on how @xmath12 and the total uncertainty behave as a function of @xmath23 . henceforth , it is crucial at this point also to take into account systematic uncertainties in the analysis in order to know if the selection cut is useful or not . however , since a full realistic simulation of the systematic uncertainty would require a detailed simulation of the detector , which is beyond the scope of this work , we use a simpler model which is enough to lead us to the desired interplay between @xmath12 , @xmath23 and statistic and systematic uncertainties in order to decide whether the selection is suitable or not . under this scenario , for the setup of the problem and its solution , it will be enough to consider @xmath17 processes up to parton level including isr . hadronization , detector simulation and reconstruction would be useful only if one could perform a fully realistic detector simulation including its systematic uncertainties . this is left for the experimental groups in case they consider to follow the guidelines in this work . the purpose of this article is to show that exists an interplay between a selection cut on the three variables @xmath2 , @xmath3 and @xmath4 and the statistic and systematic uncertainties , that yields an optimal cut which enhances the sensitivity of the @xmath9-spectrum to np that couples to quarks . we show along the article that this interplay , and therefore also the optimal cut , is strongly dependent on the energy of the process and the accumulated luminosity . for instance , we show that for the 2012 lhc data , as the energy increases beyond @xmath24 tev , strong cuts in @xmath2 should be gradually replaced by mild cuts in @xmath4 . this article is divided as follows . in next section we present the analytic results for the angular distributions in the standard model ( sm ) for quark - annihilation and @xmath25-fusion . we also study angular distribution of np models which couple to quarks and not to gluons . in section 3 , we study the parton level variables @xmath2 , @xmath3 and @xmath4 and their interplay with @xmath12 and @xmath23 , as well as the relationships of these two with the uncertainties . in section 4 , we present an example of a resonant np in @xmath8 production and show how the progressive cuts in the studied variables leads to the visibility of the resonant bump . section 5 contains a discussion on the results and previous works , and section 6 the conclusions .

we perform a general parton level analysis for the search of heavy resonant states in the production of pairs at the lhc with an integrated luminosity of 30 fb . we assume the existence of resonances that only couple to quarks and propose kinematic cuts in order to increase the amount of events produced through quark - annihilation . we study the interplay between different variables and their impact on the purity of the selected sample . finally , we illustrate the analysis with a gluon resonance of 1.5 tev and show the improvement in the sensitivity of the signal when cuts on are imposed . * top - antitop resonance searches beyond 1 tev * + + _ conicet , ifiba and departamento de fsica , fceyn , universidad de buenos aires , + ciudad universitaria , pab.1 , ( 1428 ) buenos aires , argentina _ + _ iflp , conicet - dpto . de fsica , universidad nacional de la plata , + c.c . 67 , 1900 la plata , argentina _ + e - mail : sequi@df.uba.ar , jisanchez@df.uba.ar , szynkman@fisica.unlp.edu.ar

we perform a general parton level analysis for the search of heavy resonant states in the production of pairs at the lhc with an integrated luminosity of 30 fb . we assume the existence of resonances that only couple to quarks and propose kinematic cuts in order to increase the amount of events produced through quark - annihilation . we study the interplay between different variables and their impact on the purity of the selected sample . we make focus on the longitudinal ( ) and transverse ( ) momentum of the pair , and the scattering angle ( ) in the center of mass reference frame . we observe that is replaced by as a suitable discriminating variable of quark - annihilation processes for invariant masses above 1 tev . finally , we illustrate the analysis with a gluon resonance of 1.5 tev and show the improvement in the sensitivity of the signal when cuts on are imposed . * top - antitop resonance searches beyond 1 tev * + + _ conicet , ifiba and departamento de fsica , fceyn , universidad de buenos aires , + ciudad universitaria , pab.1 , ( 1428 ) buenos aires , argentina _ + _ iflp , conicet - dpto . de fsica , universidad nacional de la plata , + c.c . 67 , 1900 la plata , argentina _ + e - mail : sequi@df.uba.ar , jisanchez@df.uba.ar , szynkman@fisica.unlp.edu.ar

1412.1103

c

the distribution of matter at small scales may provide insights on the nature of dark matter particles and potentially constrain scenarios alternative to the standard cold dark matter paradigm . in this work we have performed a first study of the nonlinear clustering of late - forming dark matter using a suite of high - resolution n - body simulations . the main phenomenological feature of this scenario is the presence of damped acoustic oscillations at large wave numbers in the linear matter power spectrum . the scale where such a power suppression occurs depends on the epoch of the phase transition of a scalar field coupled to relativistic particles that generates the dm particles . without requiring an extreme fine - tuning of the microscopic model parameters , this may occur before matter - radiation equality and imprint a pattern of damped oscillations at @xmath21 h mpc@xmath2 in the initial conditions . because of this , lfdm models are indistinguishable from standard cdm on large scales , while they are constrained by probes of the small - scale clustering of matter . from the analysis of n - body simulations , we have shown that lfdm could be a viable alternative to cdm , as it provides predictions of the nonlinear matter power spectrum largely consistent with bounds from high - redshift lyman-@xmath0 power spectrum measurements . it should be noted that the lyman-@xmath0 constraints have so far been obtained for a restricted class of dm models ( such as wdm ) with a sharp cutoff in the linear power spectrum . as lfdm models have spectra with considerably shallower slopes than wdm , it is very likely that lfdm models that resolve @xmath4cdm inconsistencies on galactic and subgalactic scales would also be in better agreement with lyman-@xmath0 measurements . we have evaluated the halo abundance ; comparison with predictions from the standard @xmath4cdm model shows that small - mass lfdm halos ( @xmath116<10^{10}$ ] ) are less abundant than their cdm counterparts . we have also evaluated the corresponding differences in the circular velocity function at @xmath20 and shown that the lfdm scenario is in better agreement with observations of the number density of low - velocity galaxies than @xmath4cdm . the number density of low - mass halos varies with redshift , with low - mass halo abundance up to @xmath117 smaller than @xmath4cdm at @xmath118 . this indicates that halos in this mass range form later than in @xmath4cdm , thus leading to lower densities in the internal part of the halos as confirmed by the study of density profiles . on the other hand , the assembly of more massive halos occurs as in @xmath4cdm , and we find no significant differences in their density profiles between the two cosmologies . these results confirm previous numerical studies of nonstandard dm models characterized by initial linear matter power spectra similar to that of lfdm . since lfdm behaves as a collisionless component , the lack of cored profiles in milky way like halos seems inherently related to the fact that in order to satisfy the lyman-@xmath0 constraints , the suppression of power in the initial power spectrum must occur on wave number @xmath119 h mpc@xmath2 . this suggests that only by including dm self - interactions would it be possible to develop cored profiles . on the other hand , one should note that baryonic feedback does play a role at these scales . given the differences in the abundance and assembly of small - mass halos in @xmath4-lfdm and @xmath4cdm , it will be of interest to investigate the dynamics of baryons in the lfdm scenario . this may leave distinct observational features in the formation of stars and galaxies which warrant further investigation . we would like to thank matteo viel and jess zavala for useful comments and suggestions . this work was granted access to hpc resources of idris through time allocations made by genci ( grand quipement national de calcul intensif ) on the machine ada no . we acknowledge support from the dim acav of the region le - de - france . the research leading to these results has received funding from the european research council under the european community s seventh framework programme ( fp7/2007 - 2013 grant agreement no . 279954 ) .

we perform a study of the nonlinear clustering of matter in the late - forming dark matter ( lfdm ) scenario in which dark matter results from the transition of a nonminimally coupled scalar field from radiation to collisionless matter . the analysis of the lfdm halo velocity function shows a better agreement than thecdm prediction with the observed abundance of low - velocity galaxies in the local volume . halos with mass h m show minor departures of the density profiles fromcdm expectations , while smaller - mass halos are less dense , consistent with the fact that they form later than theircdm counterparts .

we perform a study of the nonlinear clustering of matter in the late - forming dark matter ( lfdm ) scenario in which dark matter results from the transition of a nonminimally coupled scalar field from radiation to collisionless matter . a distinct feature of this model is the presence of a damped oscillatory cutoff in the linear matter power spectrum at small scales . we use a suite of high - resolution n - body simulations to study the imprints of lfdm on the nonlinear matter power spectrum , the halo mass and velocity functions and the halo density profiles . the model largely satisfies high - redshift matter power spectrum constraints from lyman- forest measurements , while it predicts suppressed abundance of low - mass halos ( h m ) at all redshifts compared to a vanillacdm model . the analysis of the lfdm halo velocity function shows a better agreement than thecdm prediction with the observed abundance of low - velocity galaxies in the local volume . halos with mass h m show minor departures of the density profiles fromcdm expectations , while smaller - mass halos are less dense , consistent with the fact that they form later than theircdm counterparts .

hep-th0109125

i

noncommutative field theories@xcite@xcite are obtained in an @xmath7 limit of the open string theory . this noncommutativity is inherent in the open string theory@xcite . by considering an open string in an ns - ns @xmath0 field background and taking a specific field theory limit the effects of the @xmath0 field are encoded into a special multiplication rule of functions , the @xmath8 product or moyal product . by studying such field theories we expect that open string physics may be understood in the framework of field theory . until recently such investigations are mostly restricted to constant @xmath0 backgrounds@xcite@xcite@xcite@xcite . the algebra of the coordinates of the end points of the open string was studied , the connection of the commutative and noncommutative descriptions of the gauge theory was elucidated , and so on . when the @xmath0 field is constant , the background metric @xmath9 is flat . attempts to extend the analysis to the curved background , _ i.e. _ , the nonvanishing @xmath0 field strength @xmath1 , appeared in the context of open string theory in wzw models@xcite . in this approach it was found that the algebra of functions on the d - brane worldvolume is given by the @xmath10-deformation of the lie algebra . the general framework for general backgrounds was , however , not yet obtained . more recently a noncommutative field theory for a weak field strength @xmath11 and a weakly curved background was investigated@xcite . term were also considered in @xcite and the related underlying geometry was called h - poisson or twisted poisson one . ] several correlation functions of the string theory are obtained in the @xmath12 limit and it was concluded that the algebra of functions on the d - brane worldvolume is non - associative and noncommutative . various correlation functions are expressed in terms of a non - associative product @xmath13 . in @xcite the commutation relations of the coordinate @xmath14 of the end point of the open string were studied by using the approximation of a very short and slowly moving string . it was found that the commutators of the coordinate @xmath14 contain a momentum @xmath3 and it was argued that the space on which the d - brane lives is not the usual noncommutative space which we are getting used to . in @xcite a new product @xmath15 was defined in order to make the product @xmath13 associative on the functions of @xmath14 and @xmath3 and an attempt to define a gauge transformation in this ` @xmath14-@xmath3 space ' was presented . an explicit construction of the gauge theory action , however , was not obtained yet . the purpose of the present paper is to understand how the low energy effective theory can be formulated as an associative and noncommutative gauge theory , when the background space is curved and the field strength @xmath1 along the direction of the d - brane worldvolume is nonvanishing . our analysis will be restricted to the bosonic string . we assume that the field strength is weak and perform analysis in perturbation series in @xmath11 up to @xmath16 . we will first obtain the commutation relations of the coordinates @xmath17 , @xmath18 of the two ends ( at @xmath19 and @xmath20 ) of the open string in the low energy limit.(sec 2 ) this will be performed by discarding the oscillators of the string variable @xmath21 , but without further approximation . the result is striking . @xmath17 and @xmath18 do not commute with each other in contrast to the @xmath5 case . this means that when we take the @xmath12 limit , the gauge and scalar degrees of freedom at both ends of the string are not decoupled in the low energy effective theory . we are forced to take into account the degrees of freedom at both ends in constructing the field theory description and the numbers of gauge and scalar fields are doubled . furthermore the noncommutative product @xmath2 constructed according to the algebra of @xmath14 and @xmath22 is _ associative _ , but operates on both coordinates.(sec 3 ) we are thus lead to consider a bi - local field theory . all fields are functions of @xmath14 and @xmath22 . the gauge theory must be formulated in the 2@xmath6 dimensional @xmath23 space instead of the ordinary @xmath6 dimensional @xmath14 space . this bi - local field theory will , however , be acausal and must be regarded as an intermediate step toward construction of the local effective field theory , which will be discussed later . construction of this bi - local gauge theory can be performed in a standard way . the derivatives are generalized in such a way that they satisfy leibnitz rule with respect to the product @xmath2.(sec 4 ) the commutator of the gauge covariant derivatives defined in terms of these new derivatives gives the gauge field strength.(sec 5 ) the trace or the integral is defined in such a way that the cyclic property is respected . an obstruction in this prescription is the curved d - brane worldvolume . the metric of the effective gauge theory is the open string metric@xcite , which is curved already at @xmath24@xcite . because the gauge symmetry of the noncommutative gauge theory is realized by differential operators on the fields , if the action contains such a non - constant metric , one anticipates that the gauge symmetry may be broken . remarkably , we found that there exists a coordinate transformation in the @xmath25 space ( not in the @xmath17 space ) which effectively makes @xmath5 . in other words in a suitably chosen frame @xmath26 the coordinates satisfy the commutation relations of the @xmath5 theory . therefore it is natural to further assume that the metric is flat in this frame . moreover the derivatives with respect to @xmath27 and @xmath28 coincide with the new derivatives defined above to satisfy leibnitz rule . by writing down the action for the noncommutative gauge theory with @xmath29 in the flat @xmath30 frame and by going to the @xmath23 frame by means of the inverse coordinate transformation , we obtain the action for a bi - local , noncommutative gauge theory in curved backgrounds . as mentioned above , the above bi - local theory is non - local and will be acausal . next we will present a prescription to reduce our bi - local theory to a ` local theory'.(sec 6 ) actually , in order to obtain a massless string we must consider a limit @xmath31 . this is not automatically achieved in the @xmath12 limit . we will set @xmath32 by hand in the integrand of the effective action and integrate this over @xmath14 with a suitable weight function @xmath33 . we will show cyclic property of this reduced effective action which relates various correlation functions of the fields at @xmath14 and @xmath22 , _ i.e. _ , at both ends of the string . this reduced effective action is still invariant under a part of the gauge transformation . we propose this as the low energy effective action of the open string in the @xmath34 background . this reduced effective action , however , contains @xmath2 in the integrand and the manipulation such as differentiation with respect to @xmath14 and/or @xmath22 must be performed before setting @xmath32 . in this sense this reduced effective action is not the ordinary action in the @xmath14 space . finally in sec 7 we will speculate on the relation of our noncommutative gauge theory to the matrix model in curved backgrounds .

the degrees of the freedom associated with both ends are not decoupled and accordingly , the effective action must be quite different from that of the ordinary noncommutative gauge theory for a constant background . we will then propose a prescription for reducing this bi - local effective action to that in dimensions and obtaining a local effective action .

we point out that when a d - brane is placed in an ns - ns field background with non - vanishing field strength ( ) along the d - brane worldvolume , the coordinate of one end of the open string does not commute with that of the other in the low energy limit . the degrees of the freedom associated with both ends are not decoupled and accordingly , the effective action must be quite different from that of the ordinary noncommutative gauge theory for a constant background . we construct an associative and noncommutative product which operates on the coordinates of both ends of the string and propose a new type of noncommutative gauge action for the low energy effective theory of a d-brane . this effective theory is bi - local and lives in twice as large dimensions ( ) as in the case . when viewed as a theory in the-dimensional space , this theory is non - local and we must force the two ends of the string to coincide . we will then propose a prescription for reducing this bi - local effective action to that in dimensions and obtaining a local effective action . maketitle 2em title 1.5em .5em [ cols="^ " , ] 1.5em = -1 cm = 1.5 cm = -.0 cm = 15.5 cm

gr-qc0404080

i

investigations on how the spacetime structures would be during and after gravitational collapses are important topics in gravitational physics and spacetime physics . nonlinear nature of gravity is making our understanding of the phenomena very difficult , both conceptually and technically . steady development of numerical methods is contributing to our deeper understanding on the phenomena . however , it does not mean the analytical investigations are becoming less meaningful . on the contrary , the more the numerical results we get , the more variety of analytical investigations is needed to interpret them and to reach the whole understanding of the phenomena . in this respect , we have not yet obtained enough variety of mathematical models for gravitational collapses which can be studied , mainly by analytical methods . indeed , the cases of just spherical collapses with various matter content is already complicated enough , and investigations are still going on @xcite . it can be inferred from this situation that constructing and analyzing other types of models may not be an easy task . as the next step in this direction , cylindrical collapses have been investigated considerably . this class of collapsing models are important because elongated matter distribution can drastically alter the destination of the gravitational collapse . already in the newtonian gravity , the jeans scale plays a vital role and the elongated matter longer than its jeans scale tends to split into smaller scale objects . in the case of general relativity , there is the so - called hoop conjecture " @xcite ; black holes are formed when and only when the matter of mass @xmath3 is contained in a compact region whose circumference @xmath4 in any direction always satisfies @xmath5 . therefore it is of great importance to study the fate of the collapsing elongated matter , such as cylindrical collapses . the numerical investigation of the collapse of the non - rotating dust spheroid by shapiro and teukolsky @xcite suggested that the naked singularities could emerge when sufficiently elongated object collapses . this numerical result motivated further analytical investigations on the cylindrical collapses . here , in view of the cosmic - censorship hypothesis @xcite , investigations on more natural " conditions , rather than non - rotating cases , are of significance . in particular , the effect of rotation and the effect of matter pressure should be studied . then , an analytical model of collapsing cylindrical shell made of counter - rotating dust particles was investigated by apostolatos and thorne @xcite . ( here counter - rotating particles " indicates the situation in which the half of the particles are rotating in the opposite direction to the other half of the particles . ) it takes into account the rotation of particles through the rotational pressure , while the net angular - momentum of the shell is kept zero . by avoiding the frame - dragging effect in this manner , the analysis can be relatively simple . it turned out that even a small amount of rotation prevents the singularity formation as far as this particular model concerned . another analytical model of cylindrical gravitational collapses was presented and briefly studied by pereira and wang @xcite . this model has interesting features in that not only has it taken into account both the rotation and the pressure effect , but it also tries to take into account the radiation of gravitational waves and massless particles from the collapsing region . indeed , the numerical work suggests that the gravitational radiation becomes important after the bounce of the cylindrical shell @xcite . in spite of several interesting features , however , this model has not yet been properly investigated so far . since this model is what is investigated in this paper , let us briefly recall their work @xcite . firstly they prepare general formulas in the coordinate system @xmath6 for matching arbitrary two cylindrical spacetimes . here junction conditions @xcite play the central role . then they apply the formulas to look at a particular model . in this model , an interior flat spacetime and an exterior cylindrical spacetime are matched together at @xmath7 . the geometry of the exterior spacetime is so chosen that there is out - going flux which can be interpreted as gravitational waves and massless particles ( see sec.[sec:3 ] for the details of this model ) . then a dynamical equation for the shell is explicitly derived ( see eq.([eq : pw - dynamical1 ] ) in sec.[sec:4 ] ) . since this non - linear equation is complicated enough , a very special class of solutions is searched for , and three types of special solutions are claimed to be found . they are the solutions of ( i ) a collapsing shell which bounces back at some finite radius , followed by an eternal expansion afterwards , ( ii ) an eternally expanding shell , and ( iii ) a collapsing shell whose radius reaches zero , resulting in a line - like singularity formation @xcite . the solution ( iii ) looks in particular interesting , since it reminds us of the result of numerical calculations by shapiro and teukolsky @xcite , though the spacetime structures in these two cases are not the same . considering several interesting features of the model , it is quite regrettable that their investigation is a preliminary one in nature with the limitation to the very special class of solutions , and moreover it turns out that the derivation of the special solution faces with crucial problems , which could totally alter the main results ( see sec.[sec:4 ] for the detailed account on this point ) . thus it is meaningful to analyze this model in detail . with these situations in mind , the present paper aims mainly two goals . firstly , we set up a general framework for analyzing cylindrical shell collapses in the same spirit as pereira and wang @xcite , but paying more attention to the mutual relations of three kinds of natural frames of reference . they are ( 1 ) the ortho - normal frame @xmath8 associated with the cylindrical spacetime geometry , ( 2 ) the ortho - normal frame @xmath9 associated with a shell @xmath10 in question ( here @xmath11 is the normal unit 4-vector to the shell @xmath10 , while @xmath12 is the 4-vector tangent to the world - line of an observer located on the shell ) , and ( 3 ) the coordinate frame @xmath13 . computations based on the frame ( 1 ) can be carried out systematically , while the frame ( 2 ) is more suitable for interpreting the results . therefore the bridge between them would be helpful . the frame ( 3 ) has been also considered since it is often convenient for actual computations . the second purpose of this paper is to analyze the above - mentioned model , based on the framework we prepare , and investigate the dynamical behavior of the collapsing shell . we assume that the weak energy condition @xcite is satisfied outside the shell . it means , roughly speaking , that the collapsing matter behaves as normal source of gravity . it shall be proved that , _ the collapsing shell bounces back at some point irrespective of the initial conditions , and escapes from the singularity formation_. the behavior after the bounce depends on the sign of the shell pressure in the z - direction , @xmath0 . when @xmath1 , the shell continues accelerated expansion , and its velocity asymptotically tends to the light velocity . on the other hand , when @xmath14 ( i.e. tension ) , the behavior after the bounce could be more complicated depending on the details of the model . in either case , the shell never reaches the zero - radius configuration , contrary to the result ( the solution ( iii ) mentioned above ) of the preliminary analysis in refs . @xcite and @xcite . in sec.[sec:2 ] , the fundamental formulas on the cylindrical spacetime and the cylindrical shell in it are derived . we in particular pay attention to the extrinsic curvature of the shell , which plays the central role for studying the shell dynamics . the junction conditions , which is another essential part for the shell dynamics , are also investigated there . based on the framework so prepared , then , we investigate in detail a particular model of a collapsing cylinder in sec.[sec:3 ] . in particular , we prove a theorem that the shell never reaches the singularity in this model as far as the weak energy condition is satisfied outside the shell . section [ sec:4 ] is devoted to the detailed comparison between the present analysis and the one reported in refs . @xcite and @xcite , pinpointing why the latter had been led to the virtual singular solution . section [ sec:5 ] is devoted for summary .

the model has been introduced previously but has been awaiting for proper analysis . here the analysis is put forward : it is proved that , as far as the weak energy condition is satisfied outside the shell , the collapsing shell bounces back at some point irrespective of the initial conditions , and escapes from the singularity formation . the behavior after the bounce depends on the sign of , the shell pressure in the z - direction . when , the shell continues to expand without re - contraction . on the other hand , when ( i.e. it has a tension ) , the behavior after the bounce can be more complicated depending on the details of the model .

we prepare a general framework for analyzing the dynamics of a cylindrical shell in the spacetime with cylindrical symmetry . based on the framework , we investigate a particular model of a cylindrical shell - collapse with rotational pressure , accompanying the radiation of gravitational waves and massless particles . the model has been introduced previously but has been awaiting for proper analysis . here the analysis is put forward : it is proved that , as far as the weak energy condition is satisfied outside the shell , the collapsing shell bounces back at some point irrespective of the initial conditions , and escapes from the singularity formation . the behavior after the bounce depends on the sign of , the shell pressure in the z - direction . when , the shell continues to expand without re - contraction . on the other hand , when ( i.e. it has a tension ) , the behavior after the bounce can be more complicated depending on the details of the model . however , even in this case , the shell never reaches the zero - radius configuration .

gr-qc0404080

i

in this paper , we have studied the dynamics of a cylindrical shell in the spacetime cylindrical symmetry . we have started with constructing a general framework for analyzing a cylindrical spacetime and a shell in it , which might be useful for future investigations . based on the framework , we have investigated a cylindrical shell - collapse model which accompanies the out - going radiation of gravitational waves and massless particles . this model had been introduced by pereira and wang @xcite , but its proper analysis had been awaited . this model could be interpreted as a thin shell filled with radiation . in connection with the cosmic - censorship hypothesis , we are mostly interested in the collapse of normal " matter , so that the weak energy condition has been assumed outside the shell . it has been proved that , as far as the weak energy condition is satisfied outside the shell , the shell bounces due to the rotational - pressure effect . after the bounce , it continues to expand without re - contraction when the pressure of the shell in the z - direction @xmath0 satisfies @xmath371 , while in the case @xmath14 , the behavior after the bounce can be more complicated . however in either case , the shell never reaches the zero - radius configuration and it escapes from the line - like singularity formation . just as the case of a shell filled with counter - rotating dust particles considered by apocatopolas and thorne @xcite , the present case also shows a bouncing due to the effect of rotational pressure , while the eternal expansion after the bounce ( when @xmath1 ) is a unique feature of the present model . we have also performed numerical investigations which reveal explicit behaviors of the shell . the author would like to thank s. jhingan for valuable discussions at the beginning stage of this work . he also thanks h. sakuragi for valuable discussions on numerical investigations . important part of work has been completed during the author s stay at institute of cosmology , tufts university . he is grateful for its nice hospitality . in particular he would like to thank a. vilenkin for helpful suggestions on the interpretation of the results . this work has been supported by the japan ministry of education , culture , sports , science and technology with the grant # 14740162 .

we prepare a general framework for analyzing the dynamics of a cylindrical shell in the spacetime with cylindrical symmetry . based on the framework , we investigate a particular model of a cylindrical shell - collapse with rotational pressure , accompanying the radiation of gravitational waves and massless particles . however , even in this case , the shell never reaches the zero - radius configuration .

we prepare a general framework for analyzing the dynamics of a cylindrical shell in the spacetime with cylindrical symmetry . based on the framework , we investigate a particular model of a cylindrical shell - collapse with rotational pressure , accompanying the radiation of gravitational waves and massless particles . the model has been introduced previously but has been awaiting for proper analysis . here the analysis is put forward : it is proved that , as far as the weak energy condition is satisfied outside the shell , the collapsing shell bounces back at some point irrespective of the initial conditions , and escapes from the singularity formation . the behavior after the bounce depends on the sign of , the shell pressure in the z - direction . when , the shell continues to expand without re - contraction . on the other hand , when ( i.e. it has a tension ) , the behavior after the bounce can be more complicated depending on the details of the model . however , even in this case , the shell never reaches the zero - radius configuration .

0707.2865

c

the observations of 3c227 , 327 and 390.3 almost all show differences between the structure observed in the radio and that observed in the x - ray . to summarize , the only ` simple ' hotspots seen in these three objects are the weak compact components in the e hotspot of 3c227 and ( probably ) the s hotspot of 3c390.3 , sx1 . 3c227 shows a striking 1.5-kpc offset between the radio emission from the primary w hotspot and its x - ray counterpart , in the sense that the x - ray emission is nearer the nucleus , while having similar structure in the radio and x - ray . the well - known counterpart to 3c390.3 s hotspot b turns out to have two components , neither of which is coincident with the radio or optical detection , and which are displaced from it in a direction perpendicular to the jet axis . neither of the two features most obviously related to the e hotspots of 3c327 is coincident with the peak of the radio : one is 4 kpc along the jet axis from the primary hotspot , the other at least 1 kpc away from the secondary along the primary - secondary axis . what physical processes can account for these diverse behaviors ? one possibility is of course that the compact components are nothing to do with the radio sources . this is our preferred explanation for the compact feature nx2 in 3c390.3 n ( [ nx2 ] ) : it may also explain one or , at a stretch , both of the features we see in 3c327 e , where we have no deep optical information to constrain whether a background object could be responsible . it seems very unlikely that it could account for the observations of 3c390.3 nx1 or 3c227 , where the x - ray features are clearly resolved . we therefore consider the possible emission processes that could be responsible for producing the observed x - rays from the sources themselves . as the available x - ray data suggest power - law spectra and thus non - thermal emission , we focus on inverse - compton and synchrotron processes . as discussed by @xcite in the context of the more distant double - hotspot source 3c351 ( where inverse - compton emission almost certainly plays some role in the complex x - ray structures seen ) , synchrotron self - compton emission ( ssc ) or inverse - compton scattering of the cmb ( cmbic ) can not produce offsets between the radio and x - ray unless there is very strong spatial variation in the positions of the low - energy electrons and/or important beaming effects . we first consider a model in which there are strong point - to - point variations in the number density of low - energy electrons . to produce offset x - ray emission via inverse - compton processes , we require a large population of low - energy ( @xmath112 ) electrons at the location of the x - ray emission , while either the electron spectrum or the magnetic field strength must be tuned so as to avoid significant emission from this population of electrons at radio frequencies . we used the code of @xcite to calculate the expected inverse - compton emission from components matching p1 , p2 and the x - ray source in 3c227 , using an upper limit on the radio flux density of the x - ray component of 2 mjy to normalize the radio spectrum and using the observed sizes in the radio and x - ray to choose component sizes . we modeled the three components for simplicity as uniformly filled ellipsoids in the plane of the sky . we found that for standard broken power - law spectra for the three components we require the x - ray source to have a departure from equipartition of a factor @xmath113 in magnetic field strength , and an electron energy density that is @xmath114 times greater than that in p2 , in order to produce the observed x - rays by inverse - compton processes ( where the upper limits come from the fact that we have no unambiguous detection of a radio counterpart of the x - ray source ) . in this situation we find that the dominant photon field is the cmb , and so the conclusions are robust against uncertainties in the geometry , which affect only the number density of synchrotron photons from p1/2 . such an electron distribution seems highly unlikely simply on energetic grounds , since it requires essentially all the energy in the hotspot to be concentrated in an offset , radio - invisible region . a similarly implausible electron distribution would be required for 3c327 and 3c390.3 . in addition , we show in table [ hsic ] that the parameters of all detected and non - detected hotspots predict inverse - compton flux densities ( derived using the code of @xcite ) for equipartition magnetic fields that are much less than the observed values or limits , as was shown previously in some cases by @xcite . we therefore rule out simple inverse - compton models in what follows . lllrrrrrrl [ hsic ] 3c227&w&p1&@xmath115&8.35&16&@xmath116&0.0010&0.09&offset x - ray + & & p2&@xmath117&8.35&25&@xmath116&0.0019&0.06&offset x - ray + & & p3&@xmath118&8.35&13&@xmath47&0.0014&0.02&offset x - ray + & & p4&@xmath119&8.35&1.2&@xmath50&@xmath120&0.3&jet knot ? + & e&f1&@xmath121&8.35&5.3&@xmath47&@xmath122&0.06 + 3c327&e&s1&@xmath123&8.35&15&@xmath55&@xmath124&0.02&offset x - ray + & & s2&0.32&8.35&3.2&@xmath55&@xmath125&0.09&offset x - ray + 3c390.3&n&b&@xmath126&4.99&66&@xmath59&0.003&0.08&2 sub - components + & & f&3.7&4.99&190&@xmath64&0.009&@xmath127&upper limit + & s&g@xmath65&0.5&4.99&20&@xmath50&@xmath128&0.02&offset x - ray + & s&g&0.5&4.99&36&@xmath129&0.0013&@xmath130&upper limit + & s&e&0.7&4.99&106&@xmath129&0.0056&@xmath127&upper limit + & s&d&1.2&4.99&206&@xmath64&0.011&@xmath127&upper limit + 3c403&e&f1&0.275&8.35&16&@xmath73&@xmath131&0.04 + & & f1b&0.256&8.35&7.7&@xmath75&@xmath132&0.06&jet knot ? + & & f2&@xmath133&8.35&27&@xmath77&0.0011&@xmath130&upper limit + & & f6&0.272&8.35&27&@xmath80&0.0014&0.06&jet knot + @xcite ( hereafter gk03 ) proposed to explain the x - ray properties of hotspots in objects aligned close to the line of sight using a model involving emission from the decelerating relativistic jet . at the time they were writing , there was an apparent correlation between observations of hotspots with x - ray emission too bright to be ssc in origin and the jet side of broad - line objects , such as broad - line radio galaxies and radio - loud quasars , that are expected to lie at small angles to the line of sight in unified models . since then , further observations have established that these non - ssc hotspots can occur in objects in all orientations @xcite . however , the gk03 model is still interesting because it predicts spatial offsets between the peak of the x - ray and that of the radio . they proposed that the jet decelerates on kpc scales and that x - ray emission from the fast - moving component can be produced by inverse - compton scattering of the synchrotron photons from the slower , downstream component . this external inverse - compton process is strongly directional and can only be seen if the jet is aligned close to the line of sight ( and , of course , is approaching rather than receding ) . the gk03 model should not be confused with the process of inverse - compton scattering of the cmb that has been proposed to explain the x - ray jets in core - dominated quasars ( e.g. , * ? ? ? * ) : in the gk03 model the photon energy density is dominated by synchrotron photons from the upstream hotspot , and as a consequence the beaming factors required ( for given jet properties ) are less extreme and the range of plausible angles to the line of sight can be greater . in the beamed cmb models the x - ray emission should have no particular relationship to the radio hotspot , and the angle to the line of sight of the jet is required to be small : we therefore do not consider these models further . the gk03 model might be applied to the offset between the primary hotspot of 3c227 , p1/2 , and its x - ray counterpart . 3c227 is a broad - line object , so that the lobes make a relatively small angle to the line of sight ( @xmath134 ) and , if we take p4 to be a jet knot , the only evidence that we have suggests that the w lobe is likely to contain the jet pointing towards us , though the comparatively weak radio core , the non - detection of any other components of the jet , and the presence of intrinsic absorption in the x - ray spectrum ( [ 227-core ] ) suggest that it is not at a very small angle to the line of sight ( compared to , say , 3c390.3 , with its bright radio core , unabsorbed nuclear x - ray emission and well - detected kpc - scale jet ) . the flat x - ray spectrum of the x - ray counterpart of p1/2 is consistent with an inverse - compton model . if we suppose that the jet decelerates on scales of a few kpc ( set by the observed projected size of the offset between radio and x - ray ) from relativistic to sub - relativistic speeds , is it possible that the gk03 model could explain the observed offset in 3c227 ? in principle the answer is ` yes ' since the gk03 model can explain _ any _ observation with a suitable choice of the ( observationally unconstrained ) parameters of the position - dependent bulk flow speed and electron energy spectrum of the jet . the jet would have to be quite wide at the position of p1/2 to produce the observed x - ray morphology , but not impossibly so : the distribution of emitting particles and jet velocities would also require some fine tuning in order to produce an offset x - ray peak rather than some more jet - like x - ray structure . however , we consider an explanation in terms of the gk03 model to be hard to sustain when all the observations of our sample are considered together . the secondary hotspot of 3c227 shows a similar offset , yet the bulk flow clearly can not decelerate to sub - relativistic speeds twice and the direction of any flow between the primary and secondary is not the same as the direction between p4 and p1/2 . a series of coincidences is required to explain the similarity between the primary and secondary hotspots in 3c227 , therefore . the model clearly can not explain the offsets between radio and x - ray peaks in 3c390.3 ( not in the direction of the jet ) or the offsets and variations in radio / x - ray ratio seen in 3c327 and 3c403 ( too large an angle to the line of sight ) . we conclude that the gk03 model , while not ruled out by the data for the primary hotspot of 3c227 , is of little use in providing a general explanation of the problems posed by our observations . since inverse - compton explanations seem difficult to accept , we next consider synchrotron emission . synchrotron explanations also require point - to - point electron spectrum ( or possibly magnetic field strength ) variations to account for offsets between the radio and x - ray emission . however , the magnitude of the variation is comparatively very small : the high - energy tail of the electron population responsible for the x - ray emission is energetically , and a fortiori numerically , a negligible fraction of the total , whereas for the inverse - compton process a doubling of the emissivity by adjusting the electron spectrum requires a doubling of the number density of low - energy electrons , and so effectively a doubling of the energy density of the system . energetically , therefore , it is not difficult to produce what we see via synchrotron radiation . since the electron energy loss timescale is likely to be very short ( for field strengths close to the equipartition value ) what is required to produce the observed x - ray structures is some process that can accelerate particles wherever we observe x - ray emission . as we discussed in [ intro ] , there is strong evidence from radio and optical data that hotspots are sites of particle acceleration , and their spectra are consistent with models involving a single shock followed by downstream losses . in some cases the x - ray emission from hotspots lies on an extrapolation of these models @xcite . but observations of _ diffuse _ x - ray emission , often poorly matched to the observed radio structures ( e.g. in pictor a , @xcite ; 3c33 , @xcite ; 3c390.3 s , this paper ) make it hard to sustain a model in which the particle acceleration at the hotspots is _ only _ occurring at jet termination shocks . similar conclusions have been reached by other authors based on optical data ( e.g. , * ? ? ? * ; * ? ? ? observations of compact but offset x - ray emission , as in 3c227 , present a different problem . here it seems possible that there is a discrete acceleration region that is related to the jet termination shock , but , if so , the shock is not where we would have inferred it to be from radio observations . for 3c227 we could imagine a picture in which the x - ray emission in both primary and secondary hotspots tells us where the shock is now , while the radio traces material that has passed through this shock region , expanded and decelerated . this would imply that the x - ray emission should have a radio / optical counterpart , but for a flat synchrotron spectrum ( @xmath135 ) extending between radio and x - ray the emission at other wavebands could be undetectably faint , at the 10 @xmath107jy level in the radio ( i.e. , substantially below the upper limit of @xmath136 mjy on the flux density of this component from radio maps ) . such a flat synchrotron spectrum extending all the way to the x - ray has never been observed ( precisely because of the difficulty of detecting the radio counterparts ) but might be expected in models of shock acceleration . the bulk of the optical emission in 3c227 p1/2 seems to lie in between the x - ray and radio peaks , which is qualitatively consistent with this picture . the questions to be asked are then why other hotspots seen with similar spatial resolution , such as those in 3c403 , do not show the same radio / x - ray offsets ; why the offsets in 3c327 , if they have the same origin , are so much larger ; and what the origin is of the compact structure transverse to the jet direction in the hotspot of 3c390.3 . recent numerical simulations suggest that the picture of particle acceleration in the lobes of frii sources may be less simple than in the traditional model of acceleration at strong shocks in one or more hotspots . @xcite carried out three - dimensional mhd simulations that modeled the transport of relativistic electrons and of particle acceleration at shocks . they found that the interaction of the jet and the backflowing plasma at the head of the jet produced what they called a ` shock - web complex ' , `` a region of shocks of varying strengths and sizes spread throughout the source '' . even when there was a simple terminal shock , not all the jet material necessarily passed through it , and the terminal shock was not always the strongest shock in the system . while it is not clear that their simulations are perfectly matched to real radio sources , they are capable of producing simulated synchrotron images that show apparent clear discrete multiple hotspots @xcite and in these cases the particle acceleration is not necessarily well matched to the locations of the hotspots : hotspot locations in their model can have more to do with magnetic field amplification than with particle acceleration . the notion of a ` shock - web complex ' at the head of the jet could help to explain the diffuse x - ray emission now seen in the radio - bright but non - compact source head regions of a number of objects , as discussed above , while the idea that the particle acceleration region may not always be co - spatial with the observed radio hotspot might help to explain observed offsets . it should be possible to carry out numerical simulations that allow synthetic maps of the location of high - energy synchrotron - emitting particles to be generated for qualitative comparison with the range of structures seen in x - ray observations . we can also compare the x - ray observations of hotspots with observations of systems in which the x - ray emission is almost certain to be synchrotron in origin , the fri jets ( [ intro ] ) . in the nearest fri jet , centaurus a @xcite there is direct dynamical evidence for shock - acceleration of particles , as we believe is going on in frii hotspots . there are also offsets , albeit on scales of only tens of pc rather than kpc , between the peak of the x - ray emission and the brightest radio emission , in the sense that the radio emission peaks downstream of the x - ray . and there is diffuse x - ray emission , not associated with any compact radio source or dynamical feature of the jet , which in some cases has a diffuse optical counterpart @xcite . other fri jets show similar features . at present we do not understand the nature of the radio / x - ray peak offsets in fri jets or the distributed particle acceleration process responsible for the diffuse x - ray emission , but the qualitative similarity between the cen a jet and a jet termination region like 3c390.3 s or 3c33 s means that we might hope to gain some insight into one problem by studying the other . in both cases the observational requirement is sensitive , multi - frequency observations that allow us to construct a detailed map of the synchrotron sed as a function of position . our two new targets , 3c227 and 3c327 , provide at least one clear example ( 3c227 w ) , and possibly two , of an object where the primary and secondary hotspot are both detected in the x - ray , setting aside the problem of offsets between the components . 3c33 n @xcite is another example of a source with multiple x - ray hotspots . 3c390.3 n , on the other hand , behaves more similarly to 3c403 e : the bright secondary hotspot is not an x - ray ( or optical ) synchrotron source even though there is an apparently clear connection between the primary and secondary hotspot indicative of continuing energy supply ( but cf . the discussion of this point in @xcite ) . taking sx1 and its radio counterpart g@xmath65 to be the primary hotspot of the southern hotspot complex , a similar statement can be made for this system too . in both these cases , the upper limit on the x - ray to radio flux ratio in the non - detected hotspots , which are generally brighter in the radio , is 12 orders of magnitude below the measured value for the primary hotspots ( table [ hsic ] ) . if we assume , as discussed in the previous section , that the x - ray emission mechanism is synchrotron , then this tells us that secondary hotspots can be different : some , at least , are able to accelerate particles to the highest observable energies , but others are at least an order of magnitude less efficient than the primaries in producing x - ray emission for a given radio emissivity . this conclusion would be stronger if the nature of the x - ray emission in the secondary hotspots were more obvious . if some secondary hotspots can accelerate particles to high energies and some do not , what is the difference between them ? relic hotspots left behind by a jet that has moved ( ` dentists - drill ' model ) would certainly not be expected to have high - energy particle acceleration . but in our observations one secondary that apparently is connected to the jet ( 3c390.3 n ) does not have high - energy particle acceleration , while one that has no apparent connection in sensitive radio observations ( 3c227 w ) does . radio morphology is therefore not a good guide to a hotspot s ability to accelerate particles , or to its relationship to the energy supply . nor is the radio brightness of the hotspot . one trend that is apparent in the data is that a hotspot is more likely to be an x - ray emitter ( and therefore a privileged site for high - energy particle acceleration ? ) if it is compact . the secondary hotspots in 3c227 and 3c327 are similar in size to the primaries . those in 3c390.3 and 3c403 are several times larger . ` compact ' here appears to mean less than a few kpc in size . however , though this may be a necessary condition , it is not a sufficient one , as the non - detection of relatively compact hotspots in e.g. 3c390.3 s shows . secondary hotspot compactness could thus be an indicator of relatively well - collimated continued outflow from the primary hotspot to the secondary ( or , in the case of the @xcite model , of a well - collimated disconnected jet ) ; this makes sense , since ( for a given luminosity ) a more compact hotspot is more overpressured with respect to the lobe material and will have a shorter timescale for disappearance via adiabatic expansion in the absence of the energy supply . but the lack of a one - to - one correlation reinforces what we already know from observations of single hotspots : the ability of even low - luminosity , low-@xmath137-field hotspots , even when clearly connected to the energy supply , to produce x - ray emission is very variable and must depend on details of the microphysics that are not yet accessible to us .

we find that in fact some secondary hotspots are x - ray sources , and thus probably locations for high - energy particle acceleration after the initial jet termination shock . in detail , though , we show that the spatial structures seen in x - ray are not consistent with nave expectations from a simple shock model : the current locations of the acceleration of the highest - energy observable particles in powerful radio galaxies need not be coincident with the peaks of radio or even optical emission .

we present _ chandra _ observations of a small sample of nearby classical double radio galaxies which have more than one radio hotspot in at least one of their lobes . the x - ray emission from the hotspots of these comparatively low - power objects is expected to be synchrotron in origin , and therefore to provide information about the locations of high - energy particle acceleration . in some models of the relationship between the jet and hotspot the hotspots that are not the current jet termination point should be detached from the energy supply from the active nucleus and therefore not capable of accelerating particles to high energies . we find that in fact some secondary hotspots are x - ray sources , and thus probably locations for high - energy particle acceleration after the initial jet termination shock . in detail , though , we show that the spatial structures seen in x - ray are not consistent with nave expectations from a simple shock model : the current locations of the acceleration of the highest - energy observable particles in powerful radio galaxies need not be coincident with the peaks of radio or even optical emission .

0707.2865

c

we have looked with very high spatial resolution at the hotspot x - ray emission from a small sample of radio galaxies that show multiple radio hotspots . as in earlier work , we argue that the x - ray emission from the hotspots comes predominantly from the synchrotron process , and so traces high - energy particle acceleration . to our knowledge this paper represents the first attempt to use synchrotron emission to probe the particle acceleration properties in a sample of frii sources , though several individual objects have previously been studied in detail . * the cores and lobes of the two new sources in our sample have x - ray properties that are entirely consistent with expectations and with the sources places in unified models . there is evidence for intrinsic absorption in the spectrum of the blrg 3c227 . * all the target sources exhibit structure in the x - ray images of their hotspots that would not have been predicted in a simple model in which particle acceleration occurs only at the jet termination as traced by the bright radio hotspot . this structure ranges from small - scale offsets in the radio and x - ray peaks ( e.g. in 3c227 w or 3c390.3 n ) through diffuse x - ray emission that is not well correlated with compact radio structure ( e.g. 3c390.3 s : see also 3c33 s , @xcite ; pictor a e , @xcite ) to point - like sources in the jet termination region that bear little obvious relationship to the current radio hotspots ( 3c327 e ) . if most or all of these structures can be taken to indicate the location of particle acceleration in these sources , then our observations support models in which the particle acceleration history in friis can be complicated , non - localized , and not well traced by radio observations . * our observations were obtained to investigate the nature of multiple hotspots , and we have found some evidence that some secondary hotspots are indeed associated with acceleration of particles to the highest observable energies , while others ( as we had found previously ) are not . this implies that at least some secondary hotspots have ongoing access to a supply of energy . all x - ray - synchrotron emitting hotspots appear to be compact , but not all compact hotspots are detected in x - rays . we can not at present say whether this is because some of these compact hotspots are true relics , disconnected from the energy supply , or whether they are x - ray faint for some other reason related to the microphysics of their particle acceleration . sensitive multi - wavelength observations in radio and optical will be required to make further progress . we are very grateful to karl - heinz mack for providing us with optical images of the hotspots of 3c227 prior to publication and for helpful discussion of the radio - optical alignment . we thank an anonymous referee for constructive comments that helped us to improve the paper . we also gratefully acknowledge financial support for this work from the royal society ( research fellowship for mjh ) and nasa ( grant go6 - 7094x to rpk ) . allen , s.w . , fabian , a.c . , idesawa , e. , inoue , h. , kii , t. , & otani , c. , 1997 , , 286 , 765 black , a.r.s . , baum , s.a . , leahy , j.p . , perley , r.a . , riley , j.m . , & scheuer , p.a.g . , 1992 , , 256 , 186 blandford , r.d . , & rees , m.j . , 1974 , , 169 , 395 brunetti , g. , bondi , m. , comastri , a. , pedani , m. , varano , s. , setti , g. , & hardcastle , m.j . , 2001 , , 561 , l157 brunetti , g. , mack , k.h . , prieto , m.a . , & varano , s. , 2003 , , 345 , l40 cohen , m.h . , ogle , p.m. , tran , h.d . , goodrich , r.w . , & miller , j.s . , 1999 , , 118 , 1963 cox , c.i . , gull , s.f . , & scheuer , p.a.g . , 1991 , , 252 , 588 crawford , c.s . , & fabian , a.c . , 1995 , , 273 , 827 croston , j.h . , hardcastle , m.j . , harris , d.e . , belsole , e. , birkinshaw , m. , & worrall , d.m . , 2005 , , 626 , 733 evans , d.a . , worrall , d.m . , hardcastle , m.j . , kraft , r.p . , & birkinshaw , m. , 2006 , , 642 , 96 fanaroff , b.l . , & riley , j.m . , 1974 , , 167 , 31p georganopoulos , m. , & kazanas , d. , 2003 , , 589 , l5 [ gk03 ] hardcastle , m.j . , & croston , j.h . , 2005 , , 363 , 649 hardcastle , m.j . , alexander , p. , pooley , g.g . , & riley , j.m . , 1997 , , 288 , 859 hardcastle , m.j . , birkinshaw , m. , & worrall , d.m . , 1998 , , 294 , 615 hardcastle , m.j . , birkinshaw , m. , & worrall , d.m . , 2001 , , 323 , l17 hardcastle , m.j . , birkinshaw , m. , cameron , r. , harris , d.e . , looney , l.w . , & worrall , d.m . , 2002 , , 581 , 948 hardcastle , m.j . , evans , d.a . , & croston , j.h . , 2006 , , 370 , 1893 hardcastle , m.j . , harris , d.e . , worrall , d.m . , & birkinshaw , m. , 2004 , , 612 , 729 hardcastle , m.j . , kraft , r.p . , & worrall , d.m . , 2006 , , 368 , l15 hardcastle , m.j . , worrall , d.m . , kraft , r.p . , forman , w.r . , jones , c. , & murray , s.s . , 2003 , , 593 , 169 harris , d.e . , leighly , k.m . , & leahy , j.p . , 1998 , , 499 , l149 harris , d.e . , et al . , 2000 , , 530 , l81 heavens , a.f . , & meisenheimer , k. , 1987 , , 225 , 335 jahoda , k. , mccammon , d. , dickey , j.m . , & lockman , f.j . , 1985 , , 290 , 229 kataoka , j. , & stawarz , l. , 2005 , , 622 , 797 kraft , r.p . , hardcastle , m.j . , worrall , d.m . , & murray , s.s . , 2005 , , 622 , 149 kraft , r.p . , birkinshaw , m. , hardcastle , m.j . , evans , d.a . , croston , j.h . , worrall , d.m . , & murray , s.s . , 2007 , in press ( astro - ph/0701458 ) leahy , j.p . , black , a.r.s . , dennett - thorpe , j. , hardcastle , m.j . , komissarov , s. , perley , r.a . , riley , j.m . , & scheuer , p.a.g . , 1997 , , 291 , 20 leahy , j.p . , & perley , r.a . , 1995 , , 277 , 1097 lonsdale , c.j . , & barthel , p.d . , 1986 , , 92 , 12 mack , k .- h . , prieto , m.a . , & brunetti , g. , 2003 , newar 47 501 meisenheimer , k. , rser , h .- j . , hiltner , p.r . , yates , m.g . , longair , m.s . , chini , r. , & perley , r.a . , 1989 , , 219 , 63 murphy , e.m . , lockman , f.j . , laor , a. , & elvis , m. , 1996 , , 105 , 369 nicastro , f. , fiore , f. , perola , g.c . , & elvis , m. , 1999 , , 512 , 136 prieto , m.a . , 1997 , , 284 , 627 prieto , m.a . , & kotilainen , j.k . , 1997 , , 491 , l77 prieto , m.a . , brunetti , g. , & mack , k.h . , 2002 , sci 298 193 rser , h .- j . , & meisenheimer , k. , 1987 , , 314 , 70 sambruna , r.m . , eracleous , m. , & mushotzky , r.f . , 1999 , , 526 , 60 saslaw , w.c . , tyson , j.a . , & crane , p. , 1978 , , 222 , 435 scheuer , p.a.g . , 1982 , in heeschen , d.s . , wade c.m . , eds , extragalactic radio sources , iau symposium 97 , reidel , dordrecht , p. 163 spinrad , h. , djorgovski , s. , marr , j. , & aguilar , l. , 1985 , , 97 , 932 stark , a.a . , gammie , c.f . , wilson , r.w . , bally , j. , linke , r.a . , heiles , c. , & hurwitz , m. , 1992 , , 79 , 77 tavecchio , f. , maraschi , l. , sambruna , r.m . , & urry , c.m . , 2000 , , 544 , l23 tregillis , i.l . , jones , t.w . , & ryu , d. , 2001 , , 557 , 475 tregillis , i.l . , jones , t.w . , ryu , d. , & park , c. , 2002 , newar 46 387 williams , a.g . , & gull , s.f . , 1985 , , 313 , 34

the x - ray emission from the hotspots of these comparatively low - power objects is expected to be synchrotron in origin , and therefore to provide information about the locations of high - energy particle acceleration . in some models of the relationship between the jet and hotspot the hotspots that are not the current jet termination point should be detached from the energy supply from the active nucleus and therefore not capable of accelerating particles to high energies .

we present _ chandra _ observations of a small sample of nearby classical double radio galaxies which have more than one radio hotspot in at least one of their lobes . the x - ray emission from the hotspots of these comparatively low - power objects is expected to be synchrotron in origin , and therefore to provide information about the locations of high - energy particle acceleration . in some models of the relationship between the jet and hotspot the hotspots that are not the current jet termination point should be detached from the energy supply from the active nucleus and therefore not capable of accelerating particles to high energies . we find that in fact some secondary hotspots are x - ray sources , and thus probably locations for high - energy particle acceleration after the initial jet termination shock . in detail , though , we show that the spatial structures seen in x - ray are not consistent with nave expectations from a simple shock model : the current locations of the acceleration of the highest - energy observable particles in powerful radio galaxies need not be coincident with the peaks of radio or even optical emission .

astro-ph0105043

i

the hubble deep field north ( * ? ? ? * hereafter w96 ) ranks among the most thoroughly studied portions of the extragalactic universe . the extremely deep multi color images obtained with the wfpc2 camera on the _ hubble space telescope _ , reaching ab mag @xmath5 with 0@xmath61 resolution , have revolutionized our understanding of the faint galaxy population and have yielded diverse new results in observational cosmology . follow up observations to the original survey span the electromagnetic spectrum , from the radio @xcite to the sub millimeter @xcite , to both ground and space based near infrared @xcite and far infrared @xcite . recently , x ray data have become available @xcite , and uv observations with the space telescope imaging spectrograph are in progress @xcite . in addition to imaging , numerous groups are pursuing spectroscopic observations of galaxies in the hdf . @xcite report on a magnitude limited sample more than 92% complete to vega mag @xmath7 ; @xcite and @xcite report on color selected samples of lyman break galaxies at @xmath8 ; while @xcite report on a morphologically selected sample of probable gravitational lenses . see @xcite for a review of measurements and phenomenology of sources in the hdf across the electromagnetic spectrum . consequently , the hdf and the eight adjacent , single orbit @xmath9 flanking fields ( see w96 , table 2 ) now constitute a very rich database for the study of galaxy formation and evolution . early results included the confirmation of a flattening in the slope of the faint elliptical / s0 galaxy number count magnitude relation @xcite , as well as the revealed inadequacy of the hubble sequence as a classification scheme for galaxies fainter than @xmath10 mag @xcite . the selection of four very broad bandpass filters for the wfpc2 observations was driven partly by the desire to identify high redshift galaxies via the lyman break technique . indeed , this strategy facilitated the discovery of distant galaxies whose lyman breaks have been redshifted into the @xmath11band @xcite , the @xmath12band @xcite , and beyond @xcite . the exquisite resolution of the wfpc2 images spurred considerable effort toward quantifying galaxy morphology , leading to the disentanglement of morphological @xmath13correction from morphological evolution , and revealing an increase in the fraction of true irregulars at faint magnitudes / high redshift @xcite . most recently , mining of this data rich field has yielded refined techniques in estimating photometric redshifts ( e.g. * ? ? ? * ) and has produced dramatic implications for the history of star formation @xcite as well as for the role of dust in the distant universe @xcite . we are pursuing a variety of programs to study distant galaxies in the hdf . the primary science from these observations , discussed elsewhere , includes extremely deep ( @xmath14 ) moderate and high resolution keck / lris spectroscopy of lyman break galaxies at @xmath8 aimed at understanding their stellar populations and galactic dynamics ( e.g. * ? ? ? * ) , and low resolution spectroscopy of @xmath12band and @xmath15band dropouts whose colors suggest a population of galaxies with lyman breaks and significant ly@xmath0forest absorption at @xmath16 @xcite . in the course of these observations , we have targeted more than 65 galaxies in the hdf and its environs for deep spectroscopy , and in so doing we have serendipitously observed some 125 objects which were located propitiously along the slit of a target . out of the sample of serendipitous detections , we have determined redshifts for 74 sources , with 25 galaxies in the hdf proper , 30 galaxies in the hdf flanking fields , and 19 galaxies beyond but in the vicinity of the flanking fields . thirteen of the detections in the central hdf provided the first ever spectroscopic redshift determinations for those sources . from the first detection of pulsars to the discovery of the cosmic microwave background , serendipity has historically made significant contributions to astronomy . in extra galactic astronomy in particular , dramatic serendipitous detections include the discovery of a galaxy cluster at @xmath17 @xcite , at least three quasars at @xmath18 @xcite , and the discovery of the first object at @xmath19 @xcite . serendipity plays a less dramatic but still significant role in large scale redshift surveys : serendipitous detections make up roughly 8% of the measured galaxies in the complete @xmath20 mag galaxy sample presented by @xcite . serendipitous surveys in their own right are efficient , as they require no direct initial allocation of telescope time , and they have proven to be both competitive with and complementary to narrow band imaging surveys . see @xcite , @xcite , and @xcite for reports on serendipitous searches for high redshift ly@xmath0 emission . though none of the serendipitous detections reported herein constitute singularly momentous discoveries , given the status of the hdf as ranking among the most thoroughly mapped pieces of the extragalactic universe , we would be remiss not to report all galaxy redshifts determined in the course of our observations of this well studied field . in [ data ] we discuss the spectroscopic observations and the data reduction . in [ ids ] we describe the redshift determination and the process by which the serendipitously detected galaxies were visually identified . we present the catalog of serendipitously detected galaxies in [ catalogues ] , and we discuss their distribution in redshift space , the comparison between spectroscopic and photometric redshifts , the observed properties of the galaxy cluster at @xmath21 , the observed properties of the chandra source at @xmath22 , and the candidate @xmath1 ly@xmath0emitters in [ discuss ] . throughout this paper , we adopt an einstein de sitter cosmology with @xmath23 km s@xmath24 mpc@xmath24 , @xmath25 , and @xmath26 . all quoted magnitudes are in the ab system with @xmath27 measured in erg s@xmath24 @xmath28 hz@xmath24 @xcite . the value of the constant is set by the condition @xmath29 for a flat spectrum source . ] unless otherwise specified .

we present a catalog of 74 galaxies detected serendipitously during a campaign of spectroscopic observations of the hubble deep field north ( hdf ) and its environs . among the identified objects are five candidate lyemitters at , a galaxy cluster at , and a chandra source with a heretofore undetermined redshift of . orbit hdf flanking fields . finally , we estimate the line of sight velocity dispersion and the corresponding mass and expected x ray luminosity of the galaxy cluster , we present strong arguments for interpreting the chandra source as an obscured agn , and we discuss in detail the spectrum of one of the candidate lyemitters .

we present a catalog of 74 galaxies detected serendipitously during a campaign of spectroscopic observations of the hubble deep field north ( hdf ) and its environs . among the identified objects are five candidate lyemitters at , a galaxy cluster at , and a chandra source with a heretofore undetermined redshift of . we report redshifts for 25 galaxies in the central hdf , 13 of which had no prior published spectroscopic redshift . of the remaining 49 galaxies , 30 are located in the single orbit hdf flanking fields . we discuss the redshift distribution of the serendipitous sample , which contains galaxies in the range with a median redshift of , and we present strong evidence for redshift clustering . by comparing our spectroscopic redshifts to optical / ir photometric studies of the hdf , we find that photometric redshifts are in most cases capable of producing reasonable predictions of galaxy redshifts . finally , we estimate the line of sight velocity dispersion and the corresponding mass and expected x ray luminosity of the galaxy cluster , we present strong arguments for interpreting the chandra source as an obscured agn , and we discuss in detail the spectrum of one of the candidate lyemitters .

astro-ph0105043

c

the 74 galaxies in the serendipitous catalog span the redshift range @xmath57 , with a median redshift of @xmath2 . the vast majority of the galaxies are emission - line systems ; 5% of the sample show only absorption lines . this bias stems from the diminished likelihood of serendipitously detecting an absorption line system with sufficient signal to noise to allow the redshift to be determined . we estimate that the uncertainty in the most secure redshifts ( sc 1 ) is @xmath58 . the uncertainty in redshifts based on solo emission lines or continuum breaks ( sc 2 to 5 ) assuming the identification of the spectral feature is sound is @xmath59 . for the 12 galaxies in the central hdf also observed spectroscopically by @xcite , @xcite , @xcite , or @xcite , we compared our spectroscopic redshift to the published value and found that the agreement was excellent , with a mean deviation of @xmath60 and a dispersion of @xmath61 . in all cases , the discrepancy is comparable to our estimated measurement error . the redshift distribution of the serendipitous catalog , compared with a total sample " consisting of this sample , all published redshifts for galaxies in the central hdf , and 26 published redshifts for galaxies flanking the central hdf , is shown in figures [ histo_full ] and [ histo_short ] . sources for the total sample are @xcite ; @xcite ; @xcite ; @xcite ; @xcite ; @xcite ; @xcite ; @xcite ; and @xcite . the histogram displayed in figure [ histo_full ] displays the total range of redshifts of the combined catalogs , @xmath62 , with a comparatively coarse resolution of @xmath63 . given the caveat that we are insensitive to galaxies in the redshift range @xmath52 ( cf . 3.1 ) , we find that the redshift distribution of the serendipitous sample closely follows that of the total sample . to investigate the redshift clustering properties of the serendipitous sample , we display the redshift distribution for the galaxies in the range @xmath64 with a resolution of @xmath65 in figure [ histo_short ] . the figure shows clear evidence of clustering in both the serendipitous sample and the total sample . moreover , the clustering present in the total sample is mirrored almost perfectly by that present in the serendipitous sample . assuming a fixed number of galaxies per redshift bin ( i.e. no evolution in bin membership with redshift ) , we find a @xmath66 peak in the serendipitous sample at @xmath67 , a @xmath68 peak at @xmath69 and @xmath70 , and a @xmath71 peak at @xmath72 . in total , we find that 17 out of the 51 serendipitous galaxies ( 33% ) fall into peaks significant at greater than 97.5% confidence . this figure compares favorably with that of ( * ? ? ? * hereafter c96 ) , who find that 57 out of 140 ( 41% ) of their sample of spectroscopically observed hdf galaxies fall into redshift peaks . that the locations of our peaks vary somewhat from those in c96 is not surprising . whereas c96 chose redshift bins of variable centers and widths so as to maximize their significance relative to occurring by chance in a smoothed velocity distribution , we chose fixed bin centers and widths , cf . even so , our peaks centered on @xmath73 and @xmath70 no doubt reflect the same structures revealed by the peaks in c96 at @xmath74 and @xmath75 , respectively . we find no evidence of periodicity in the peak redshifts , as described by @xcite . beyond the strong evidence of redshift clustering , there are two outstanding features of the redshift distribution of the serendipitous sample . first , there is a relative deficiency of serendipitous detections at @xmath76 . second , the redshift peak centered on @xmath77 evident in the total sample is not represented in the serendipitous sample . taken together , these features appear to suggest a selection effect which excludes galaxies at @xmath76 from serendipitous detection . however , since this redshift range is perfectly accessible to lris via the balmer lines and by [ ] and [ ] emission , it is likely that the scarcity of low redshift galaxies in the serendipitous catalog is merely the combined effect of : ( 1 ) the increasingly small cosmological volume surveyed at low redshift , ( 2 ) the comparatively small size of the serendipitous catalog , and ( 3 ) the fact that the hdf was selected to be devoid of bright galaxies in the first place . at a minimum , these facts make it impossible to comment on the significance of the apparent @xmath78 deficiency . photometric redshift techniques have become an essential tool of observational cosmology , with applications ranging from determining luminosity functions to selecting high redshift candidates for spectroscopy . we have utilized our set of spectroscopic redshifts for 23 of the 25 serendipitously detected galaxies in the central hdf to carry out a test of the photometric redshifts presented by @xcite , who employ a maximum likelihood analysis applied to spectral energy distribution fitting of precise @xmath79 , @xmath80 , @xmath81 , @xmath9 , @xmath82 ( 1.2 @xmath83 m ) , @xmath84 ( 1.65 @xmath83 m ) , and @xmath85 ( 2.2 @xmath83 m ) photometry . for two galaxies , hdf 4402.1 and hdf 4236.0 , no photometric redshift was available , no doubt owing to their faintness : @xmath86 and 28.26 , respectively . the sample of predicted redshifts was taken from the group s world wide web site the university of new south wales / state university of new york at stony brook hdf clickable mapfsoto / hdf / hdf_fs.html ] which is an interactive version of the catalog presented in the associated paper . we compare the spectroscopic redshift ( @xmath87 ) and the photometric redshift ( @xmath88 ) in a scatter plot of @xmath87 versus @xmath88 for redshifts less than 1.5 in figure [ spec_vs_phot ] . there are three obvious errors in the photometric redshifts : ( 1 ) hdf 4639.1 , listed with @xmath89 and @xmath90 , whose spectrum shows ly@xmath0 in emission with a strong continuum break ( sc 3 ) , and whose @xmath87 is confirmed by both @xcite and @xcite ; ( 2 ) hdf 2600.0 , listed with @xmath91 and @xmath92 , whose spectrum shows a strong solo emission line interpreted as [ ] @xmath453727 ( sc 4 ) ; and ( 3 ) hdf 4658.0 , listed with @xmath93 and @xmath94 , whose spectrum shows both [ ] and [ ] emission ( sc 1 ) . these outliers comprise 13% of the sample , roughly consistent with the finding of @xcite that outliers at more than 4@xmath95 in the @xmath87@xmath88 plane comprised @xmath96% of the subset of galaxies at @xmath97 . the outliers are not shown in figure [ spec_vs_phot ] , as they are off the scale . the mean and the dispersion of the difference between the predicted photometric redshifts and the measured spectroscopic redshifts are @xmath98 and @xmath99 , respectively . however , these values are dominated by the three discrepant points described above . when the discrepant points are omitted , we find a mean deviation of @xmath100 and a dispersion of @xmath101 . these errors are consistent with the assessment that cosmic variance ( the fact that the model spectra used in determining photometric redshifts represent a finite sample of all possible galaxy spectra ) rather than photometric errors is the dominant source of error at small redshift @xcite . moreover , these results confirm that barring catastrophic errors photometric redshifts are capable of producing reasonable predictions of galaxy redshifts where suitably precise multicolor photometry is available . we report the serendipitous discovery of clg 1236 + 6215 , a galaxy cluster with redshift @xmath2 nominally centered at @xmath102123639@xmath66 , @xmath103621554@xmath104 ( j2000 ) . the cluster was initially identified as an over density of centrally concentrated red objects in a small region to the northwest of the hdf in the deep hawaii 2.2 m @xmath15 and @xmath37 images of @xcite . in a circle of radius 45 arcsec centered on the cluster position , the density of objects with @xmath105 is 18 arcmin@xmath106 , versus a density of only 6.5 arcmin@xmath106 over the rest of the 90 arcmin@xmath30 hawaii 2.2 m field . we interpreted the @xmath107 color of the concentration to be the result of the 4000 break redshifted into the @xmath37band , and we targeted five of the reddest members for spectroscopy . all five of the targets proved to have redshifts very near to @xmath2 . we added three more redshifts by selecting objects from the redshift catalog of @xcite which had @xmath105 and @xmath108 , and which were located within 45 arcsec ( @xmath109 mpc ) of the cluster center . together , the eight spectroscopic members of clg 1236 + 6215 yield a mean redshift for the cluster of @xmath110 . the properties of the spectroscopic members of clg 1236 + 6215 are summarized in table [ clg ] . following the prescription of @xcite for properly considering the contributions to measured redshifts due to the radial component of the motion of our galaxy with respect to the local group , to the cosmological expansion between comoving observers at our galaxy and at the galaxy cluster , and to the radial component of the peculiar velocity of the galaxy within the cluster , we calculated an estimate of the corrected line of sight velocity dispersion in clg 1236 + 6215 . we followed the treatment of @xcite to account for the spurious systematic contribution to from measurement errors in the member redshifts . assuming an underlying gaussian distribution for the galaxy velocities , we found @xmath111 km s@xmath24 ( 68% confidence ) ; this value should be treated with caution due to the small number of spectroscopic members . @xcite point out that the classical standard deviation estimator for cluster velocity dispersions is neither resistant to the presence of outliers nor robust for non gaussian underlying populations . however , employing the gapper " method as implemented in their rostat package yields a correction which is less than our estimated uncertainty . in the limiting isothermal model , the calculated velocity dispersion translates to a mean cluster mass within a 45 arcsec ( @xmath109 mpc ) radius of the cluster center of @xmath112 . for comparison with other authors , the mean mass within the abell radius is @xmath113 . of perhaps more immediate observational consequence is the x ray luminosity expected for the given velocity dispersion . drawing on a sample of 197 galaxy clusters which constitutes the largest cluster data set used to date for such a study @xcite find @xmath114 for the x ray bolometric luminosity velocity dispersion relation . this result yields an expected x ray bolometric luminosity for clg 1236 + 6215 of @xmath115 erg s@xmath24 , a value which exceeds the expected detection threshold of the upcoming @xmath116 ms _ chandra x ray observatory _ ( cxo ) exposure of the hdf and its environs @xcite . optical spectroscopy of faint x ray sources is the key to determining the poorly understood physical properties of the population responsible for producing the x ray background . we present the first published optical spectrum and redshift for cxohdfn j123635.6@xmath44621424 , a well observed x ray source identified with a face on spiral galaxy at @xmath3 , fortuitously located in the inner west hdf flanking field . cxohdfn j123635.6@xmath44621424 was first detected as a weak radio source ( 8.15 @xmath83jy at 8.5 ghz ; 87.8 @xmath83jy at 1.4 ghz ) in the sensitive hdf radio surveys of @xcite . the source has a comparatively steep radio spectral index ( @xmath117 ; @xmath118 ) , and the radio emission extends across 2@xmath68 . in general , microjansky radio emission from disk galaxies can result from either star formation ( e.g.from free free emission originating in regions ) or from agn activity connected with a central engine . @xcite argued that ( 1 ) in the case of a central agn powering a weak ( @xmath119 w hz@xmath24 ) radio source , the bulk of the radio emission is confined to the nuclear region and is therefore characterized by sub arcsecond angular scales , and ( 2 ) such small scales result in a high opacity to synchrotron self absorption , yielding flat or inverted spectral indices typically in the range @xmath120 . hence , the origin of the radio emission in cxohdfn j123635.6@xmath44621424 was taken to be extended star forming regions . this conclusion was ostensibly borne out by an _ infrared space observatory _ camera ( isocam ) detection of the source @xcite . if the source were a moderate to low redshift starburst galaxy ( as suggested by hornschemeier 2001 , owing to the object s spatial extent ) , the isocam 15 @xmath83 m filter ( lw3 ) would sample rest wavelengths from roughly 6 @xmath83 m to 12 @xmath83 m ; the mid infrared emission could therefore be plausibly attributed to the unidentified infrared bands ( uib ) and to the hot , 200 k dust which typically dominates the spectral energy distribution of starbursts over those wavelengths @xcite . in contradistinction to the foregoing conclusions , both the optical and x ray properties of cxohdfn j123635.6@xmath44621424 indicate the presence of agn activity . the optical spectrum shows moderate width ( @xmath121 km / s ) , high ionization emission lines , similar to those of the recently reported quasar ii in the chandra deep field south @xcite and typical of high redshift radio galaxies ( cf . * ; * ? ? ? we detect ly@xmath0 , @xmath451240 , @xmath451397 , @xmath451549 , @xmath451640 , ] @xmath451909 , [ ] @xmath452424 , and @xmath452800 ( figure [ chandra_spec ] ) . moreover , the rest frame equivalent widths of the ] @xmath451908 and @xmath451548 emission lines ( @xmath122 and @xmath123 , respectively ) are within the ranges found in multiple agn emission line surveys and optical / radio quasar surveys ( see * ? ? ? * and references therein ) . we also note that the @xmath451549/ @xmath451640 ratio of @xmath124 is more typical of quasars than of radio galaxies . optical and near ir photometry of cxohdfn j123635.6@xmath44621424 corroborates these findings . @xcite give @xmath125 for the source , and @xcite report that all x ray counterparts with @xmath126 in their rosat ultra deep hri survey are either members of high redshift clusters or are obscured agn . finally , cxo observations of the source indicate a comparatively hard x ray spectrum the definitive signature of an agn . the x ray band ratio , defined as the ratio of hard band ( 2 kev to 8 kev ) to soft band ( 0.5 kev to 2 kev ) number counts , is @xmath127 , corresponding to a photon index is derived from a power law model for the x ray spectrum : @xmath128 , where @xmath129 is the number of photons s@xmath24 @xmath28 kev@xmath24 and @xmath130 is a normalization constant . ] of @xmath131 @xcite . when re interpreted in the light of the spectroscopic redshift , even the mid ir data for cxohdfn j123635.6@xmath44621424 actually indicate the presence of an agn . for the derived redshift of @xmath3 , the isocam lw3 filter samples rest wavelengths spanning only 4 @xmath83 m to 5 @xmath83 m . here , the contribution to the mid ir spectral energy distribution made by uib emission and by dust at 200 k is severely attenuated ( see * ? ? ? * figure 1 ) . hence , the isocam detection of this source is far more plausibly explained by the hot , @xmath132 k dust found in the central region of an agn ( e.g. see * ? ? ? * ) rather than by star formation alone . the weakness of ly@xmath0 in this galaxy substantiates the presence of dust in this system . though the canonical wisdom regarding extended radio sources with spectral indices steeper than @xmath133 dictates that such sources are driven by starbursts @xcite , the combined weight of evidence from x ray , optical , and near and mid ir observations of cxohdfn j123635.6@xmath44621424 is definitively in favor of an obscured agn . this conclusion is consistent with the trend reported by @xcite : that the high x ray luminosities and large band ratios of several cxo detected radio sources previously reported as starburst type objects strongly suggests the presence of heretofore unidentified agns . we are currently pursuing keck / nirspec spectroscopy of this interesting source in order to further detail its physical properties . in the course of deep , targeted spectroscopy of photometric high redshift galaxy candidates , we have identified several serendipitous high redshift ly@xmath0emitting candidates , including five sources at @xmath1 . these high redshift sources are evident in figure [ histo_full ] , and they are listed in table [ ffz ] . the surface density of such sources is sufficiently high that these discoveries are not unexpected ( e.g. * ? ? ? * ; * ? ? ? indeed , slit spectroscopy surveys for high redshift ly@xmath0 emission are fully complimentary to narrow band searches ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) : rather than probing a large area of sky for objects over a limited range of redshift , deep slit spectroscopy surveys a small area of sky for objects over a large range in redshift @xcite . the total area covered by the spectroscopic slits during the course of our study was @xmath135 arcmin@xmath136 , implying a surface density of @xmath137 arcmin@xmath106 ly@xmath0emitters at redshift @xmath138 . this value is roughly consistent with the surface density of high redshift ly@xmath0emitters reported by @xcite : @xmath139 arcmin@xmath106 ( unit@xmath140)@xmath24 at redshift @xmath141 , for comparable sensitivity to line flux . of course , one should exercise caution regarding these values , owing to the small number of detections involved . each of the high redshift sources in this catalog are solo emission line sources ( sc 4 ) , and as indicated by a handful of cautionary tales ( 3.2 herein ; also see * ? ? ? * ; * ? ? ? * ) , such redshift identifications should be greeted with a degree of circumspection . a detailed discussion of each individual source is beyond the scope of this paper , and a separate manuscript is planned . for now , we restrict the discussion to one likely high redshift source , f 362461511 at @xmath142 , as illustrative of the situation . f 362461511 was discovered in a 5400s exposure obtained on ut 19 february 1998 . the source appeared as solo emission line spatially offset by @xmath143 from an absorption line galaxy ( f 362471510 ; @xmath144 ) . a portion of the two dimensional spectrogram , centered on the emission line , is shown in figure [ serx2 ] . the top panel shows the original two dimensional spectrogram ; the continuum of the absorption line galaxy and the spatially offset emission line can be readily seen . in the bottom panel , we have subtracted a gaussian fit to the foreground continuum source . the fit was made to the continuum source only blueward of the emission line so that after subtraction assuming a locally flat spectrum for both sources any remaining flux could be attributed to the high redshift candidate . in this fashion we hoped to isolate continuum flux from the high redshift source and recover a continuum break , which would lend credence to the ly@xmath0interpretation . however , as can be seen in the one dimensional extracted spectrum ( figure [ oned ] ) , the continuum break is of low significance relative to the noise . as the emission line itself is not obviously asymmetric , the remaining evidence in favor of the ly@xmath0interpretation is two fold . to begin , the observed frame equivalent width of the line is @xmath145 . this value exceeds the largest equivalent widths observed for other likely interpretations : 200 for the h@xmath146 [ ] complex ; 100 for [ ] @xmath455007 ; and 100 for [ ] @xmath453727 @xcite . additionally , a faint source is visible in the outer west @xmath9 flanking field image ( w96 ) located at the correct separation and orientation to be the progenitor of the solo emission line . unfortunately , as the offset between the foreground continuum source and the high redshift candidate is only @xmath143 , ground based images are insufficient to resolve the two objects . hence , the only available visual identification of the high redshift candidate stems from the well resolved but comparatively shallow single orbit flanking field image . since the discovery spectrum was obtained , we have targeted f 362461511 for an additional @xmath147 ks of spectroscopy . the resulting composite spectrum confirms the @xmath148 interpretation and will appear in a future work .

we discuss the redshift distribution of the serendipitous sample , which contains galaxies in the range with a median redshift of , and we present strong evidence for redshift clustering . by comparing our spectroscopic redshifts to optical / ir photometric studies of the hdf , we find that photometric redshifts are in most cases capable of producing reasonable predictions of galaxy redshifts .

we present a catalog of 74 galaxies detected serendipitously during a campaign of spectroscopic observations of the hubble deep field north ( hdf ) and its environs . among the identified objects are five candidate lyemitters at , a galaxy cluster at , and a chandra source with a heretofore undetermined redshift of . we report redshifts for 25 galaxies in the central hdf , 13 of which had no prior published spectroscopic redshift . of the remaining 49 galaxies , 30 are located in the single orbit hdf flanking fields . we discuss the redshift distribution of the serendipitous sample , which contains galaxies in the range with a median redshift of , and we present strong evidence for redshift clustering . by comparing our spectroscopic redshifts to optical / ir photometric studies of the hdf , we find that photometric redshifts are in most cases capable of producing reasonable predictions of galaxy redshifts . finally , we estimate the line of sight velocity dispersion and the corresponding mass and expected x ray luminosity of the galaxy cluster , we present strong arguments for interpreting the chandra source as an obscured agn , and we discuss in detail the spectrum of one of the candidate lyemitters .

astro-ph0603163

r

as we described in section [ sec : confused ] , there are many definitions for the source confusion . we compare these definitions and propose an appropriate definition for source confusion . in table [ tab_inst_para ] , we list the basic instrumental parameters of present and future ir space missions ; the aperture of the telescope , full width at half maximum ( fwhm ) of the beam profile and the pixel size for each detector . @ccrlrlrl + & aperture & & & + & ( meter ) & & & + space mission & & sw & lw & sw & lw & sw & lw + + _ spitzer _ @xmath81 & 0.85 & 70 & 160 & 17 & 35 & 10 & 16 + _ akari _ @xmath82 & 0.69 & 75 & 140 & 23 & 44 & 27 & 44 + _ herschel _ @xmath83 & 3.5 & 70 & 175 @xmath84 & 4.3 & 9.7 & 3.2 & 6.4 + _ spica _ & 3.5 & 70 & 160 & 4.3 & 9.7 & 1.8 & 3.6 + _ @xmath85 _ fwhm of diffraction pattern . + _ @xmath81 _ two mips bands for the _ spitzer _ mission have 3 bands with central wavelengths of 24 @xmath0 m , 70 @xmath0 m and 160 @xmath0 m . we use 70 @xmath0 m band as sw band and 160 @xmath0 m band as lw band in this paper . + _ @xmath82 _ _ akari / fis _ ( far infrared surveyor ) has a wide - s band in sw and a wide - l band in lw . + _ @xmath83 _ pacs has a ` blue ' array in two short wavelength bands ( centered at 70 @xmath0 m and 110 @xmath0 m ) and a ` red ' array at longer wavelengths ( centered at 175@xmath0 m ) . in this paper , we use only the 70 @xmath0 m band of the ` blue ' array . + _ @xmath86 _ since one of our motivations in this paper is to compare the confusion limits , we use only common bands among all far - ir bands in the considered space missions . + _ @xmath84 _ note that though the central wavelength of the ` red ' array in pacs is 175 @xmath0 m , our estimated results are for 160 @xmath0 m . due to this wider beam , the confusion noise is expected to increase by @xmath28 15% at 175 @xmath0 m compared to that at 160 @xmath0 m . first , we estimate the source confusion from the classical definition of source confusion , beams per source ( sources per beam ) . though often cited in the literature as sources per beam , we use the term beams per source for our definition of source confusion in order to compare the effect of source confusion according to the different beam sizes for each mission . we check the source confusion by changing the number of beams per source criterion from 10 to 50 . [ fig_beam_sconf ] shows the source confusion assuming this definition for each mission and each model . hogg showed that 30 beams per source is the minimum photometric criterion where the source counts are steep , and suggested 50 beams per source for the definition of source confusion . rowan - robinson adopted 40 beams per source . in recent papers , dole et al . ( 2003 , 2004b ) suggested that source confusion could be defined by a source density criteria , corresponding to @xmath28 12 beams per source for the _ spitzer _ mission . they have estimated a source confusion limit for the _ spitzer _ mission of 3.2 mjy for sw band and 40 mjy for lw band , respectively . these results are similar to our estimations with the definition of 12 beams per source for the luminosity evolution model in the sw band and for the burst evolution model in the lw band , respectively . these consistences suggest that the source distribution model used for the estimation of the source confusion limit for the case of _ spitzer _ @xcite also predicts that a starburst component , and ulig component dominate the sw and lw bands respectively . in table [ tab_sc_beams ] , we list the source confusion limits estimated by the definition of 12 and 40 beams per source . as seen from fig . [ fig_beam_sconf ] , we found that the source confusion did not increase at a constant rate and that the slope of the source confusion slightly varies according to the source distribution model and the resolution of the mission , especially for burst evolution model . therefore , we conclude that we can not apply the same definition of beams per source in a generic way for different missions . @ccccccccccccc + & & & + & & & + & & & & & & + space mission & 12b @xmath85 & 40b @xmath81 & 12b & 40b & 12b & 40b & 12b & 40b & 12b & 40b & 12b & 40b + + _ spitzer _ & 0.53 & 1.9 & 8.8 & 23 & 2.1 & 5.1 & 17 & 34 & 6.9 & 13 & 42 & 69 + _ akari _ @xmath82 & 1.9 & 6.0 & 13 & 34 & 5.1 & 12 & 23 & 47 & 14 & 26 & 52 & 87 + _ herschel _ & _ spica _ & 0.014 & 0.066 & 0.65 & 2.1 & 0.10 & 0.47 & 2.6 & 6.8 & 0.11 & 0.65 & 4.3 & 20 + _ @xmath85 _ source confusion defined by dole et al . ( 2004b ) : flux corresponding to 12 beams per source . + _ @xmath81 _ source confusion defined by rowan - robinson ( 2001 ) : flux corresponding to 40 beams per source . + _ @xmath82 _ wide - s band for sw and wide - l band for lw . = 8.5 cm = 8.5 cm another criterion for the quantification of source confusion can be defined by the fluctuation from beam to beam due to the distribution of the point sources @xcite . since the beam size is large and the source counts are steep , the usual definition of ` beams per source ' may not be valid in the case of far - ir photometry . for the psf , we assume an ideal circular aperture airy pattern corresponding to the aperture size of the telescopes for each mission except for _ akari _ for which we use the theoretical psfs estimated from the telescope design @xcite . to visualize the iteration procedure , we plot the @xmath87 ratio as a function of @xmath88 for the _ spitzer _ and _ herschel _ & _ spica _ missions for the case of the burst evolution model ( see figure [ fig_sn_sconf ] ) . for the sw band of the _ herschel _ & _ spcia _ missions , the @xmath89 ratio is always greater than 5 , which means that we can not obtain a solution for source confusion , even for @xmath48 = 5 . dole et al . estimated the source confusion with their best estimator for the _ spitzer _ mission . with optimized @xmath48 parameters of 3.8 in sw band and 6.8 in lw band , they obtained source confusion limits of 3.2 mjy and 36 mjy at 70 @xmath0 m and 160 @xmath0 m , respectively . using our source count models and the same @xmath48 parameters , we obtained the source confusion limits of 3.7 mjy and 21 mjy for the luminosity evolution model and 12 mjy and 60 mjy for the burst evolution model at the same wavelengths . as we showed in section [ sec : sc_def_beam ] , though the source density of the source count model used in dole et al . is similar to the luminosity evolution model in the sw band and the burst evolution model in the lw band , we find that the fluctuation due to distributed sources in the burst evolution model is much stronger than that of the model of dole et al . . this amount of fluctuation may degrade the final detection limits . = 8.5 cm in table [ tab_sc_fluc ] , we list the source confusion limits estimated from the definition by fluctuation for the cases of @xmath48 = 3 and @xmath48 = 5 . for @xmath48 = 5 , there are no solutions for the sw band of _ herschel _ & _ spica _ missions . even in the lw band , we could not find a reasonable solution since the estimated source confusion for the two evolutionary models gave identical results . however , when we attempted photometry on the simulated images including the point sources for each source count model , we encountered some limits to the source detection . therefore , we conclude that we can not apply a constant @xmath48 to the estimation of source confusion generically for all cases . @ccccccccccccc + & & & + & & & + & & & & & & + space mission & @xmath48 = 3 & @xmath48 = 5 & @xmath48 = 3 & @xmath48 = 5 & @xmath48 = 3 & @xmath48 = 5 & @xmath48 = 3 & @xmath48 = 5 & @xmath48 = 3 & @xmath48 = 5 & @xmath48 = 3 & @xmath48 = 5 + + _ spitzer _ & 0.065 & 0.28 & 3.8 & 10 & 0.51 & 1.9 & 14 & 33 & 0.51 & 1.9 & 41 & 87 + _ akari _ & 0.36 & 1.4 & 5.6 & 15 & 2.4 & 6.8 & 20 & 43 & 2.4 & 23 & 59 & 115 + _ herschel _ & _ spica _ & @xmath90 @xmath85 & 0.002 & 0.042 & 0.34 & @xmath90 & 0.006 & 0.18 & 1.5 & @xmath90 & @xmath90 & 0.18 & 1.5 + _ @xmath85 _ no solution for this case . in an attempt to define the source confusion for all cases , we implement a composite definition by fluctuation and photometry . as a first step , we attempt photometry on the simulated images created from each source count model . the definition of completeness and reliability for quantifying the source detection efficiency is widely used in photometry . the ` completeness ' is defined as the fraction of detected sources to the original input catalogue sources and the ` reliability ' as the fraction of real sources to all detected sources.for our photometry , we removed the false or spurious detections by comparing the positions of detected sources with those in the input catalogue . the real sources as defined in the reliability , refers to sources of which the measured flux agrees with the input flux to within a 20% error . note that the reliability at a given flux range is not always higher than the completeness . an excess of sources near the detection limit , or more likely an overestimation of the flux of sources at or near the detection limit can be caused by a step effect where the underlying , unresolved sources are entering the psf , affecting the sky - subtraction . we carried out aperture photometry on the simulated images using the sextractor software _ _ v__2.2.2 @xcite . the most influential parameters are the size of background mesh and the threshold for the source detection for the aperture photometry . since the size of background mesh is related to the range of scales of the background fluctuation , as we set a smaller mesh size , we can detect smaller fluctuation . therefore , if we use smaller size of background mesh and thresholds , we obtained many more spurious sources . we set the size of the background mesh to @xmath28 2 times the measuring aperture , and the detection threshold as 4 , which is optimized for better reliability of the detected sources thus reducing the false detection rate . as discussed in section [ sec : sc_def_fluc ] , we could not use a constant value of @xmath48 for the estimation of source confusion . current and future space missions , will detect much fainter sources to higher sensitivity , which means that we will observe high source densities to extremely faint detectable flux levels . therefore , a significant factor contributing to the source detection comes from both the faint sources below the detection limit and the high source density above or around the detection limit . with this assumption , we include the contributed fluctuations from the sources above the detection limit as well . in order to find the limiting flux affecting the source detection , we use a photometric method on the simulated images . we set the limiting flux @xmath88 in equation [ fluctuations ] to be the flux that the completeness reaches @xmath28 80% where the completeness level abruptly falls off . we do not use the reliability criterion in this definition since the reliability can be improved by using optimized photometric methods . we also assume that the sources above this flux level do not contribute significantly to the source confusion . we obtain the final source confusion from a 4@xmath91 fluctuation in order to compare with the threshold used in the photometry . in table [ tab_sc_phot ] , we list the source confusion limits from our best estimators . @crlrlrl + & & & + & & & + space mission & sw & lw & sw & lw & sw & lw + + _ spitzer _ & 0.48 & 9.4 & 2.0 & 23 & 6.5 & 66 + _ akari _ & 2.0 & 14 & 6.3 & 33 & 17 & 87 + _ herschel _ & _ spica _ & 0.0095 & 0.63 & 0.077 & 2.2 & 0.10 & 4.4 + though we could not obtain the results for the sw band of _ herschel _ & _ spica _ missions with the original definition of the fluctuation with constant @xmath48 , we could obtain the results by our new best estimator . we also find that the source confusion limits by our definition are mostly consistent with a completeness of @xmath28 65% for all missions . therefore , we conclude that our definition can explain the behaviour of source confusion well in the far - ir range , regardless of individual space mission characteristics . in our study of sky confusion in paper i , we predicted the confusion limits considering both sky confusion due to cirrus structure and source confusion for each mission from a rather simple ( power law ) source distribution models and plotted the sky confusion levels for an assumed range of average cirrus brightness @xmath92 in table [ tab_sc_cirrus ] ( see details in paper i ) . kiss et al . have also estimated the all - sky cirrus confusion for various ir missions . [ fig_comp_kiss ] shows a comparison of sky confusion between kiss et al . and jeong et al . for the _ akari _ mission at 170 @xmath0 m . since the kiss et al . ( 2005 ) model assumes a linear relationship between the cirrus brightness and sky confusion , it often gives different results in low to medium cirrus brightness . = 7.5 cm @crlrlrl + & + & & & + space mission & sw & lw & sw & lw & sw & lw + + _ spitzer _ & 0.10 & 7.1 & 1.2 & 10 & 11 & 19 + _ akari _ & 0.73 & 9.4 & 5.4 & 18 & 27 & 42 + _ herschel _ & _ spica _ & 0.003 & 0.16 & 0.027 & 0.21 & 0.31 & 0.37 + _ @xmath85 _ mean brightness of cirrus emission since , in general , the cirrus fluctuations are not represented by gaussian noise , we can not directly sum the two noise contributions ( sky confusion and source confusion ) for the estimation of the final confusion noise . however , in a recent paper , h@xmath93raudeau et al . found that the distribution of cirrus fluctuation is near - gaussian , at least at the isophot 90 and 170 @xmath0 m spatial frequencies . thus , we use equation [ eq_tot_no ] to estimate final confusion limits @xmath94 in this paper by summation of the two confusion noise components : @xmath95 where @xmath96 is the sky confusion limit due to cirrus structure and @xmath97 is the source confusion limit . fig . [ fig_conf_all ] shows the final confusion limits due to both sky and source confusion for each mission and each evolutionary model . the sky confusion will be negligible for the _ herschel _ and _ spica _ missions even in regions of high cirrus brightness and the dominant confusion contribution is predicted to be the source confusion in high galactic latitude regions for the purpose of cosmological studies . however , care must be taken when considering the _ spitzer _ and _ akari _ missions in the mean cirrus brightness range @xmath98 @xmath99 20 mjy sr@xmath80 for the lw band . in order to check the effect caused by the combination of both sky and source confusion , we attempt photometry on the simulated images including various cirrus background levels and source count models and compare them with the photometric results considering only source confusion . these results are presented in appendix [ app : phot_results ] . = 8.5 cm = 8.5 cm we summarize the confusion limits including both sky and source confusion for each mission in table [ tab_final_sc ] for the low cirrus background regions dominated by source confusion . the mean brightness used in the estimation of sky confusion is 0.5 mjy sr@xmath80 and 1.0 mjy sr@xmath80 for the sw and lw bands , respectively . the sensitivity for the _ akari _ mission is estimated based upon the recent laboratory experiments , and various detector characteristics and observational environments which may affect the final sensitivity ( jeong et al . 2003 , 2004 ; matsuura et al . 2002 ; shirahata et al . 2004 ) . though the single scan sensitivity in survey mode of the _ akari _ mission is much lower than the confusion limit , the sensitivity at higher ecliptic latitudes where many scans overlap should approach the confusion limit . for the _ herschel _ mission , since the sensitivity is 3 mjy , we expect that most observations in the sw band will be dominated by instrumental noise and those in the lw band will be near the confusion limit . however , the _ spica _ mission will achieve the confusion limit in both bands since it will have a large aperture telescope cooled to very low temperatures @xcite . @cccrlrlrl + & & & & + & & & & + space mission & sw & lw & sw & lw & sw & lw & sw & lw + + _ spitzer _ & 6 & 15 & 0.49 & 12 & 2.0 & 25 & 6.6 & 67 + _ akari _ @xmath85 & 12 ( 200 ) & 12 ( 400 ) & 2.2 & 18 & 6.4 & 34 & 17 & 88 + _ spica _ @xmath81 & 3 & 3 & 0.010 & 0.66 & 0.077 & 2.3 & 0.10 & 4.4 + _ herschel _ @xmath82 & 3 & 3 & 0.010 & 0.73 & 0.077 & 2.6 & 0.10 & 5.1 + _ @xmath85 _ 5@xmath91 sensitivity for slow scan mode ( scan speed : 8 arcsec / sec , reset : 1 sec ) and survey mode ( parenthesized values , 1 scan ) . the sensitivity of the survey mode at high ecliptic latitude regions can be improved due to the high redundancy . + _ @xmath81 _ 5@xmath91 sensitivity without source confusion and sky confusion . in the case of the _ herschel _ & _ spica _ mission , we commonly use the 5@xmath91 sensitivity of _ herschel _ mission @xcite . + _ @xmath82 _ our actual estimations in the lw band are for those in 160 @xmath0 m . we considered the effect of wider beam at 175 @xmath0 m of the lw band . the detection limits as a function of integration time can be an important indicator of the confusion level . based upon recent hardware measurements for the _ akari _ mission and the _ spitzer _ results from dole et al . ( 2004b ) , we compare the detection limits as a function of an integration time in figure [ fig_noise_intg ] . in case of the _ akari _ mission , we also plot the results of different sampling modes for the high background regions . the decreasing component of the noise is the usual behavior of noise with increasing integration time while the flattening component is mainly due to the confusion . since a low cirrus region was assumed in this estimation , the flattening of the noise results from the source confusion . in the sw band , the detection limits are mostly determined by the instrumental noise and the source confusion noise irrespective of the amount of cirrus background except for the very highest cirrus regions , i.e. near the galactic plane . however , in the lw band , we find that the sky confusion affects the noise level severely in the regions brighter than @xmath28 20 mjy sr@xmath80 for the _ akari _ mission and @xmath28 30 mjy sr@xmath80 for the _ spitzer _ mission , respectively ( see also the plot of confusion limits in fig . [ fig_conf_all ] ) . if the different sampling mode for high background regions available for the _ akari _ mission is used , the detection limits are mostly limited by instrumental and photon noises in the sw band unless the exposure time is very long . however , in the lw band , we found that the sky confusion limits compete with the instrumental and photon noises even for short exposure observations . = 6.5 cm = 6.5 cm = 6.5 cm = 6.5 cm

we present a comprehensive analysis for the determination of the confusion levels for the current and the next generation of far - infrared surveys assuming three different cosmological evolutionary scenarios . we use our derived sensitivities to suggest best survey strategies for the current and the future far - infrared space missions _ spitzer _ , _ akari _ ( _ astro - f _ ) , _ herschel _ , and _ spica_. we discuss whether the theoretical estimates are realistic and the competing necessities of reliability and completeness . we find the best estimator for the representation of the source confusion and produce predictions for the source confusion using far - infrared source count models . from these confusion limits considering both source and sky confusions ,

we present a comprehensive analysis for the determination of the confusion levels for the current and the next generation of far - infrared surveys assuming three different cosmological evolutionary scenarios . we include an extensive model for diffuse emission from infrared cirrus in order to derive absolute sensitivity levels taking into account the source confusion noise due to point sources , the sky confusion noise due to the diffuse emission , and instrumental noise . we use our derived sensitivities to suggest best survey strategies for the current and the future far - infrared space missions _ spitzer _ , _ akari _ ( _ astro - f _ ) , _ herschel _ , and _ spica_. we discuss whether the theoretical estimates are realistic and the competing necessities of reliability and completeness . we find the best estimator for the representation of the source confusion and produce predictions for the source confusion using far - infrared source count models . from these confusion limits considering both source and sky confusions , we obtain the optimal , confusion limited redshift distribution for each mission . finally , we predict the cosmic far - infrared background ( cfirb ) which includes information about the number and distribution of the contributing sources . [ firstpage ] cosmology : observations infrared : galaxies galaxies : evolution ism : structure methods : observational

0805.2980

i

there is currently considerable interest in preparing exotic quantum states of many - body systems which can be used as resource states for measurement - based quantum computation ( mbqc ) that is , quantum computation that proceeds solely through local adaptive measurements on single quantum systems @xcite . the canonical example of such a resource state is the cluster state @xcite , which is a universal resource for mbqc on suitable lattices or graphs @xcite . it may be possible to prepare such a cluster state dynamically in atomic systems such as an optical lattice @xcite or using single photons @xcite however , one exciting possibility is that such resource states might be the non - degenerate ground state of a `` natural '' hamiltonian lattice system . if the system is gapped , then one simply needs to cool it sufficiently in order to obtain the desired state ( although , even for gapped systems , this cooling process may be difficult @xcite ) . consider the cluster state on a lattice @xmath0 , defined as the unique @xmath1 eigenstate of a set of stabilizer operators @xmath2 , where @xmath3 ( @xmath4 ) is the pauli @xmath5 ( @xmath6 ) operator at site @xmath7 and where @xmath8 denotes that @xmath9 is connected to @xmath7 by a bond in the lattice @xmath0 . the hamiltonian @xmath10 with @xmath11 an energy constant , has the cluster state as its unique ground state @xcite . in addition , this system is gapped ( the gap is @xmath12 ) , and such a system can be cooled efficiently @xcite . however , for any non - trivial lattice or graph , this hamiltonian involves many - body interactions , as opposed to the two - body interactions that occur frequently in nature . an obvious question , then , is whether it is possible to realize any given highly - entangled quantum state as the ground state of a hamiltonian with only two - body interactions . et al . _ @xcite proved that this is not possible in general , and nielsen @xcite used this result to prove that a cluster state on a computationally universal ( i.e. , two - dimensional or higher ) lattice can not arise as the ground state of a hamiltonian with only two - body interactions . however , investigations into quantum complexity theory @xcite have demonstrated that cluster states ( and other such states that are universal ) can be _ approximated _ by the ground state of a local two - body hamiltonian . the key idea is to make use of `` mediating '' ancilla qubits to create an effective many - body coupling out of two - body interactions . the problem with such methods is that the detailed parameters in the perturbing hamiltonian must be controlled with a precision that increases with the size of the system @xcite , making such approaches impractical for the task of creating cluster states on large lattices . using an alternate method based on the idea behind projected entangled pair states ( peps ) @xcite , bartlett and rudolph @xcite proved that it was possible to obtain a state that closely approximates an _ encoded _ cluster state on a square lattice using a hamiltonian with only two - body nearest - neighbour interactions . in addition , they proved that mbqc can proceed using such an encoded resource state , still requiring only adaptive single - qubit measurements . in this paper , we present a general method for constructing two - body nearest - neighbour hamiltonian systems for which the ground state encodes a cluster state , based on the techniques of @xcite . our rigorous application of perturbation theory reveals errors in the calculation of the energy gap for the square lattice investigated in @xcite ( although these errors do not affect their key result ) and we provide a correct treatment of this case . we also investigate the cluster state on a one - dimensional line ( useful for illustration , as well as for its application as a quantum wire @xcite ) , a hexagonal lattice in two - dimensions a universal mbqc resource with the best scaling of the energy gap in perturbation , and the cubic lattice in three - dimensions a resource state for which fault - tolerance thresholds have been found @xcite . we explicitly characterise the effects of fixed boundary conditions on the lattice , proving that such boundary conditions do not affect the main result . finally , we provide an outline of a proof that this method yields an encoded cluster state as the ground state on any graph .

we present a general procedure for constructing lattices of qubits with a hamiltonian composed of nearest - neighbour two - body interactions such that the ground state encodes a cluster state . we give specific details for lattices in one- , two- , and three - dimensions , investigating both periodic and fixed boundary conditions , as well as present a proof for the applicability of this procedure to any graph .

we present a general procedure for constructing lattices of qubits with a hamiltonian composed of nearest - neighbour two - body interactions such that the ground state encodes a cluster state . we give specific details for lattices in one- , two- , and three - dimensions , investigating both periodic and fixed boundary conditions , as well as present a proof for the applicability of this procedure to any graph . we determine the energy gap of these systems , which is shown to be independent of the size of the lattice but dependent on the type of lattice ( in particular , the coordination number ) , and investigate the scaling of this gap in terms of the coupling constants of the hamiltonian . we provide a comparative analysis of the different lattice types with respect to their usefulness for measurement - based quantum computation .

1403.0005

i

we have presented a green s function formalism , which can correctly describe two required conditions for any consistent theory of bose einstein condensates ( becs ) : ( i ) the infrared divergence of the longitudinal susceptibility in the low - energy and low - momentum limit , as well as ( ii ) the nepomnyashchii nepomnyashchii ( nn ) identity , which states the vanishing off - diagonal self - energy in the same limit . these conditions can not be satisfied in the bogoliubov mean - field theory , the many - body @xmath0-matrix theory ( mbta ) , as well as the random - phase approximation ( rpa ) with the vertex correction . our key idea is to divide the irreducible self - energy contribution into the singular and non - singular parts with respect to the infrared divergence . these self - energies are separately included in the green s function so as to satisfy various conditions that are required for any consistent theory of becs . in this paper , we treated the non - singular self - energy as the ordinary self - energy correction in the green s function . on the other hand , we dealt with the singular self - energy to the first - order . the resulting green s function consists of two terms , which is similar to the green s function in the popov s hydrodynamic theory @xcite . the singular component mentioned above enables us to correctly describe the infrared divergence of the longitudinal susceptibility , the hugenholtz - pines relation , as well as the nn identity . in addition , we showed that the non - singular part of the self - energy provides the enhancement of the bec phase transition temperature @xmath6 ( which has been predicted by various methods ) . the value of the enhancement depends on to what extent we take into account many - body corrections in the non - singular self - energy . the present approach can describe various required conditions that are not satisfied in the previous theories , such the bogoliubov - type mean - field theory , the mbta , as well as the rpa with the vertex correction . on the other hand , it still has room for improvement in considering the region near @xmath6 . when the non - singular self - energy is treated within the mbta , the expected second - order phase transition may be obtained , whereas the enhancement of @xmath6 is overestimated compared with the monte - carlo simulation result . when the non - singular part is calculated within the rpa with the vertex correction , the enhancement of @xmath6 is close to the monte - carlo result compared with the mbta , whereas it incorrectly gives the first - order phase transition . the further improvement of the present approach to overcome this problem is a remaining issue . we thank m. ueda for valuable discussions and comments . we also thank a. leggett and y. takada for discussions . s.w . was supported by jsps kakenhi grant number ( 249416 ) . y.o . was supported by grant - in - aid for scientific research from mext in japan ( 25400418 , 25105511 , 23500056 ) .

we present a green s function formalism for an interacting bose einstein condensate ( bec ) satisfying the two required conditions : ( i ) the infrared - divergent longitudinal susceptibility with respect to the bec order parameter , and ( ii ) the nepomnyashchii these conditions can not be described by the ordinary mean - field bogoliubov theory , the many - body-matrix theory , as well as the random - phase approximation with the vertex correction . in this paper , we show that these required conditions can be satisfied , when we divide many - body corrections into singular and non - singular parts , and separately treat them as different self - energy corrections .

we present a green s function formalism for an interacting bose einstein condensate ( bec ) satisfying the two required conditions : ( i ) the infrared - divergent longitudinal susceptibility with respect to the bec order parameter , and ( ii ) the nepomnyashchii nepomnyashchii identity stating the vanishing off - diagonal self - energy in the low - energy and low - momentum limit . these conditions can not be described by the ordinary mean - field bogoliubov theory , the many - body-matrix theory , as well as the random - phase approximation with the vertex correction . in this paper , we show that these required conditions can be satisfied , when we divide many - body corrections into singular and non - singular parts , and separately treat them as different self - energy corrections . the resulting green s function may be viewed as an extension of the popov s hydrodynamic theory to the region at finite temperatures . our results would be useful in constructing a consistent theory of becs satisfying various required conditions , beyond the mean - field level .

1201.0910

i

previously , we have compared the quality of fit provided by atmospheric models , high resolution synthetic spectra , and spectral energy distributions ( seds , @xmath4 ) computed both in lte , and with many opacity sources treated in self - consistent non - lte ( nlte ) , for the the sun and the standard stars procyon ( @xmath5 umi ) and arcturus ( @xmath5 boo ) ( @xcite , @xcite , @xcite ) . we found that our lte models tend to increasingly predict too much blue and near - uv band flux as @xmath1 decreases , and that the problem is exacerbated by non - lte effects ( mainly the non - lte over - ionization of , as is well explained in the case of the sun ( see , for example , @xcite ) ) . however , their conclusions were weak because of the small number of stars covering a few haphazard points in stellar parameter space ( @xmath6 $ ] ) . @xcite ( hereafter paper i ) took a first step toward making the investigation more comprehensive by comparing a large grid of lte model seds spanning the cool side of the hr diagram to observed seds taken from the extensive uniformly re - calibrated spectrophotometric catalog of @xcite . they investigated lte models and synthetic seds computed with two choices of input atomic lines list : a larger , lower quality `` big '' list , and a smaller , higher quality `` small '' list , and found that the models computed with the `` small '' line list provide greater internal self - consistency among different spectral bands , and closer agreement with the less model - dependent @xmath1 scale of @xcite , but not to the interferometrically derived @xmath1 values of @xcite . they also found that to within the limits of the observed spectrophotometry , there was no evidence of a systematic over - prediction of blue and near - uv band flux among gk giants in general , but they did confirm the over - prediction for arcturus ( their `` k1.5iii-0.5 '' sample ) . [ [ section ] ] here we take the next step by carrying out a similar comparison for a large grid of models seds with many important extinction sources treated in self - consistent nlte ( see @xcite for a description of these atmospheric models and spectra with h , he , and two or more of the lowest ionization stages of c , n , o , and most of the light metals and the fe - group elements treated in self - consistent multi - species non - lte statistical equilibrium . ) our goal is to map out the goodness of fit , and the magnitude of any systematic discrepancies between model and observed seds , as a function of the three stellar parameters , @xmath1 , @xmath2 , and @xmath7 $ ] , this time for nlte models , and to compare the results to those of lte modeling . we also compare our @xmath1 values inferred from sed fitting to less model - dependent @xmath1 calibrations . one important goal is to determine where in the upper right quadrant of the hr diagram nlte effects become most important .

we present a grid of atmospheric models and synthetic spectral energy distributions ( seds ) for late - type dwarfs and giants of solar and 1/3 solar metallicity with many opacity sources computed in self - consistent non - local thermodynamic equilibrium ( nlte ) , and compare them to the lte grid of ( paper i ) .

we present a grid of atmospheric models and synthetic spectral energy distributions ( seds ) for late - type dwarfs and giants of solar and 1/3 solar metallicity with many opacity sources computed in self - consistent non - local thermodynamic equilibrium ( nlte ) , and compare them to the lte grid of ( paper i ) . we describe , for the first time , how the nlte treatment affects the thermal equilibrium of the atmospheric structure ( relation ) and the sed as a finely sampled function of , , and $ ] among solar metallicity and mildly metal poor red giants . we compare the computed seds to the library of observed spectrophotometry described in paper i across the entire visible band , and in the blue and red regions of the spectrum separately . we find that for the giants of both metallicities , the nlte models yield best fit values that are 30 to 90 k lower than those provided by lte models , while providing greater consistency between values , and , for arcturus , values , fitted separately to the blue and red spectral regions . there is marginal evidence that nlte models give more consistent best fit values between the red and blue bands for earlier spectral classes among the solar metallicity gk giants than they do for the later classes , but no model fits the blue band spectrum well for any class . for the two dwarf spectral classes that we are able to study , the effect of nlte on derived parameters is less significant . we compare our derived values to several other spectroscopic and photometric calibrations for red giants , including one that is less model dependent based on the infrared flux method ( irfm ) . we find that the nlte models provide slightly better agreement to the irfm calibration among the warmer stars in our sample , while giving approximately the same level of agreement for the cooler stars .

0905.3556

i

gas transport to the centers of galaxies is still mainly an unsolved problem ( e.g. * ? ? ? since most of this gas is residing in a rotating disk well beyond the center , it is essentially a problem of angular momentum transport . proposed transport mechanisms range from galactic interactions and bars , to nuclear bars and spirals , to stellar mass loss and disruption near the central black hole ( bh ) . this range in scales also closely represents a range in decreasing mass inflow rates , which in turn might be correlated with activity in the galactic nucleus ( agn ) , ranging from quasar , seyfert , liner to quiescent galaxies . however , not only is it challenging to ( observationally ) establish fueling mechanisms down to a few parsec from the center , time delays between changes in the mass inflow rate and the onset of nuclear activity further complicate linking them . it is also likely that multiple fueling mechanisms are important and act together . large - scale bars are efficient at transporting gas inward ( e.g. * ? ? ? * ) , but the presence of an inner lindblad resonance ( ilr ) will cause the gas to pile up in a nuclear ring , often clearly visible due to the intense star formation ( see e.g. figure [ fig : images ] ) . the gas might continue further inward through nested bars ( e.g. * ? ? ? * ; * ? ? ? * ) , although dynamical constraints on a double - barred system may prohibit inflow down to the center @xcite . moreover , observational evidence of nuclear bars is scarce ( e.g. * ? ? ? * ; * ? ? ? * ) , but should be interpreted with care since the prominent dust lanes in the main bar might be absent in secondary bars ( e.g. * ? ? ? on the other hand , nuclear spirals seem to be commonly observed , both in active and quiescent galaxies ( e.g. * ? ? ? * ) , ranging from flocculent to grand - design nuclear spirals ( e.g. * ? ? ? whereas the former are suggested to form by acoustic instabilities ( e.g. * ? ? ? * ) , the grand - design nuclear spirals are thought to be the result of gas density waves ( e.g. * ? ? ? * ) or shocks ( e.g. * ? ? ? * ; * ? ? ? * ) induced by the non - axisymmetric gravitational potential of a large - scale bar . the latter two might be connected in the sense that the bar - driven spiral shocks trigger the gas density waves throughout the disk @xcite , which in turn seem to be necessary for the nuclear spiral to be long - lived @xcite . the inward extended gas inflow through a nuclear spiral not only depends on the torque of the large - scale bar , but also the gas having high enough sound speed so as to loose angular momentum ( e.g. * ? ? ? * ; * ? ? ? * ) , as well as the presence of a central mass concentration such as a super - massive bh to overcome a closer - in ( inner ) ilr ( e.g. * ? ? ? * ; * ? ? ? the deviations in the gas density due to nuclear spirals are typically only a few per cent @xcite , which makes direct imaging very difficult . instead , the obscuration due to dust thought to be associated with the gas overdensities is often employed , but when the extinction is small or the dust not well - mixed with the gas , it can lead to unclear or even missed detections of nuclear spirals . at the same time , nuclear spirals induce non - circular motions in the gas , with resulting deviations in the observed velocity field that can be a significant fraction of the underlying circular velocity . if the gas is ionized , the kinematics might be inferred from emission lines , which in general can be detected more easily and at higher spatial resolution in the optical , than can be tracers of the molecular or atomic gas such as co and hi at radio wavelengths . moreover , while imaging typically only yields a detection of the nuclear spiral , the observed non - circular motions in combination with the gas ( over)density inferred from the simultaneously measured ( line ) fluxes might be used to derive an estimate of the gas mass in / out - flow rate . an alternative approach to get a handle on the gas flow rates is to compute the gravitational torques from the observed surface brightness using a mass - to - light ratio conversion calibrated against ( circular ) velocity measurements @xcite , or against stellar population models fitted to color measurements @xcite . in these cases , various assumptions are made , most importantly that stellar light is a clean ( once corrected for dust obscuration ) and direct ( mass follows light ) tracer of the underlying gravitational potential . even so , this approach shows that gravitational torques due to non - axisymmetric structures are very efficient at transporting gas inward while overcoming dynamical barriers such as the corotation resonance . however , when the resulting predicted mass inflow rates as functions of radius are compared with the non - circular motions in the observed gas velocity fields the correlation between both is often not evident @xcite . the main difficulty with the non - circular motions is to identify the fraction that is due to pure radial flow . gas on closed elliptic orbits not only contributes to non - circular motions ( or elliptic streaming ) in the azimuthal direction but also in the radial direction @xcite . however , since closed elliptic orbits are applicable strictly only to collisionless ( stellar ) orbits , we expect that as a result of shocks and other dissipational effects the angular momentum of the gas will change , leading to in / out - flow . while the measured non - circular motions are often taken to be directly representative of the radial flow velocities ( e.g. * ? ? ? * ) , only a fraction of them are expected to be truly radial in / out - flows . the goal of this paper is two - fold : ( i ) to show that harmonic expansion of gas velocity fields provides a clean way to detect nuclear spirals and to estimate their pitch angles ; ( ii ) to use simple perturbation models to constrain the fraction of measured non - circular motions that is due to radial flow , and to estimate the corresponding mass inflow rate . in section [ sec : harmanalysis ] we present the harmonic analysis , and in section [ sec : ngc1097 ] we apply it to the observed emission - line velocity field within the circumnuclear starforming ring of ngc1097 . we find that the three - arm spiral structure in the non - circular motions is consistent with a weak two - arm spiral perturbation of the gravitational potential , and use the model derived in appendix [ app : gasorbits ] to constrain the inflow rate as function of distance from the center of ngc1097 . in section [ sec : discussion ] we discuss the corresponding spiral distortion in the surface brightness , and possible additional non - circular motion contributions to the velocity field . finally , we link the estimated mass inflow rate to the accretion onto the central bh of ngc109 . we summarize and draw our conclusions in section [ sec : summaryandconcl ] .

three_-arm spiral in the non - circular motions , which agrees with a _ this nuclear spiral is consistent with a weak perturbation in the gravitational potential due to a two - arm logarithmic spiral , with a pitch angle of derived directly from the harmonic expansion of the velocity field . next , we use a simple spiral perturbation model to constrain the fraction of the measured non - circular motions that is due to radial inflow .

we present a harmonic expansion of the observed line - of - sight velocity field as a method to recover and investigate spiral structures in the nuclear regions of galaxies . application to the emission - line velocity field within the circumnuclear starforming ring of ngc1097 , obtained with the gmos - ifu spectrograph , reveals a _ three_-arm spiral in the non - circular motions , which agrees with a _ two_-arm dust spiral in the surface brightness . this nuclear spiral is consistent with a weak perturbation in the gravitational potential due to a two - arm logarithmic spiral , with a pitch angle of derived directly from the harmonic expansion of the velocity field . next , we use a simple spiral perturbation model to constrain the fraction of the measured non - circular motions that is due to radial inflow . we combine the resulting inflow velocity with the gas density in the spiral arms , inferred from emission line ratios , to estimate the mass inflow rate as a function of radius , which reaches aboutmyr at a distance ofpc from the center . this corresponds to a fraction of about of the eddington mass accretion rate onto the central black hole in ngc1097 , and is fully consistent with previous mass accretion models fitted to the observed spectral energy distribution in the nucleus of this liner / seyfert1 galaxy . we conclude that the line - of - sight velocity not only can provide a cleaner view of nuclear spirals than the associated dust , but that the presented method also allows the quantitative study of these possibly important links in fueling the centers of galaxies , including providing a handle on the mass inflow rate as a function of radius .

0905.3556

i

we presented harmonic expansion of the line - of - sight velocity field as a suitable method to identify and quantify possible structures in the non - circular motions , including nuclear spirals . we showed that a weak perturbation in the gravitational potential of harmonic number @xmath47 , causes the surface brightness to also exhibit @xmath47 distortion , but leads to @xmath64 and @xmath65 harmonic terms in the velocity field . in the case of a @xmath47-arm spiral perturbation in the gravitational potential , we found that the corresponding @xmath94-arm and @xmath95-arm spirals in the velocity field are respectively less and more tightly wound , with pitch angles approximately related as @xmath250 . in appendix [ app : gasorbits ] , we derived an analytic perturbation model , which allows for a simple estimate of the fraction of the measured non - circular motions that is due to radial flow . we applied this method to the emission - line velocity field within the circumnuclear starforming ring of ngc1097 , obtained with the gmos - ifu spectrograph . the resulting non - circular motions reveal a _ three_-arm spiral structure , and from the corresponding @xmath217 harmonic terms , we measure a pitch angle @xmath136@xmath1 . we linked the @xmath210 and @xmath217 harmonic terms in the velocity field to a weak perturbation of the gravitational potential due to a two - arm nuclear spiral with an inferred pitch angle @xmath251@xmath1 . we showed that this agrees with a two - arm dust spiral in ( optical ) images of the center of ngc1097 , although additional spiral structure might be present as a result of higher - order even harmonic terms . we argued that it is unlikely that the presence of also @xmath137 harmonic terms in the velocity field is due to lopsidedness in the gravitational potential nor in the nuclear spiral itself , which we expect to be due to long - lived density waves in the gas driven by the bi - symmetric large - scale bar . instead , we postulated that an asymmetric dust obscuration mimics a lopsided distortion , and gives rise to the additional even harmonic terms in the velocity field . to match the measured odd harmonic terms in the velocity field of ngc1097 , a spiral perturbation model with a large amount of radial damping is required . this indicates both strong dissipation and , that , in addition to elliptic streaming , a significant fraction of the non - circular motions is due to radial inflow . we combined the inferred radial inflow velocity with the gas density in , and the geometry of , the spiral arms to estimate the mass inflow rate as function of radius . we calculated the gas density from the variation in the flux ratio of the emission - line doublet , and we incorporated in the geometry the scale - height assuming a marginally stable disk . the resulting mass inflow rate decreases to @xmath252m@xmath3yr@xmath4 at a distance of @xmath241pc from the center . we showed that this corresponds to @xmath253 , where the latter eddington accretion rate is onto a black hole in ngc1097 with a mass @xmath233m@xmath3 based on the central stellar velocity dispersion . this rate is fully consistent in general with the active galactic nucleus in ngc1097 varying between liner and seyfert1 , and in particular with previous mass accretion models fitted to the observed spectral energy distribution in its nucleus . we conclude that the line - of - sight velocity can provide not only a cleaner view on nuclear spirals than does the associated dust , but that the presented method also allows one to quantitatively study these possibly important links in fueling the centers of galaxies , including a handle on the mass inflow rate as a function of radius .

we present a harmonic expansion of the observed line - of - sight velocity field as a method to recover and investigate spiral structures in the nuclear regions of galaxies . application to the emission - line velocity field within the circumnuclear starforming ring of ngc1097 , obtained with the gmos - ifu spectrograph , reveals a _ this corresponds to a fraction of about of the eddington mass accretion rate onto the central black hole in ngc1097 , and is fully consistent with previous mass accretion models fitted to the observed spectral energy distribution in the nucleus of this liner / seyfert1 galaxy . we conclude that the line - of - sight velocity not only can provide a cleaner view of nuclear spirals than the associated dust , but that the presented method also allows the quantitative study of these possibly important links in fueling the centers of galaxies , including providing a handle on the mass inflow rate as a function of radius .

we present a harmonic expansion of the observed line - of - sight velocity field as a method to recover and investigate spiral structures in the nuclear regions of galaxies . application to the emission - line velocity field within the circumnuclear starforming ring of ngc1097 , obtained with the gmos - ifu spectrograph , reveals a _ three_-arm spiral in the non - circular motions , which agrees with a _ two_-arm dust spiral in the surface brightness . this nuclear spiral is consistent with a weak perturbation in the gravitational potential due to a two - arm logarithmic spiral , with a pitch angle of derived directly from the harmonic expansion of the velocity field . next , we use a simple spiral perturbation model to constrain the fraction of the measured non - circular motions that is due to radial inflow . we combine the resulting inflow velocity with the gas density in the spiral arms , inferred from emission line ratios , to estimate the mass inflow rate as a function of radius , which reaches aboutmyr at a distance ofpc from the center . this corresponds to a fraction of about of the eddington mass accretion rate onto the central black hole in ngc1097 , and is fully consistent with previous mass accretion models fitted to the observed spectral energy distribution in the nucleus of this liner / seyfert1 galaxy . we conclude that the line - of - sight velocity not only can provide a cleaner view of nuclear spirals than the associated dust , but that the presented method also allows the quantitative study of these possibly important links in fueling the centers of galaxies , including providing a handle on the mass inflow rate as a function of radius .

1702.06957

c

using data taken with the sdss boss spectrograph , we have compiled a new empirical stellar template library . our template library : * covers spectral types o5 through l3 * includes dwarf and giant separation for spectral types a0 through m8 * contains metallicity [ fe / h ] bins for spectral types a3 through m8 * reports averaged photometric colors ( in sloan bands ) for all the co - added stars in each template , along with a propagated errors and standard deviations along with the templates , we have released the pyhammer code for assigning a spectral type and metallicity automatically ( or by visual inspection ) . this code is based on the hammer " spectral typing facility , written by @xcite , but includes metallicity information and is now written in python . the automatic spectral typing portion of code returns the exact spectral type we determined using the original hammer " code and metallicity we determined using the methods described in section [ metallicity ] over 50% of the time . the spread in the spectral type was 1.5 spectral sub - types , and a spread in the metallicity was 0.4 dex . visual spectral typing allows for direct comparison between input spectra and our empirical templates in an easy to use gui . the code is available on github . the library of empirical stellar spectra will be important for a wide range of research topics from extragalactic to galactic astronomy , planetary system stellar characterization , and even as an astronomical teaching tool . with large photometric surveys such as lsst , machine learning techniques will become increasingly important to quickly characterize large amounts of data . along with releasing our templates , we will provide lists of the individual boss spectra co - added to construct each template . this combination of information will be an ideal training set for machine learning , and can extend the work of @xcite on f , g , and k stars to both higher and lower mass stars . the templates also provide the necessary tool for characterizing stellar populations in other galaxies , especially for studies of the imf . scrutiny of the low - mass end of the imf , has led many people to suggest it changes form in different environments ( i.e. different metallicity environments ) . our catalog represents the first empirical template library with metallicity and surface gravity separation for low - mass ( m - type ) stars . the catalog and the new pyhammer " spectral typing facility will be a useful tool for the community as a whole . the authors would like to thank phil muirhead and chris theissen for reading this manuscript and providing much helpful feedback . the authors would also like to thank dylan morgan , chris theissen , conor robinson and philip phipps for help developing the pyhammer " code . a.a.w . also acknowledges the support of the nsf grants ast-1109273 and ast-1255568 along with research corporation for science advancement s cottrell scholarship . funding for the sdss and sdss - ii has been provided by the alfred p. sloan foundation , the participating institutions , the national science foundation , the u.s . department of energy , the national aeronautics and space administration , the japanese monbukagakusho , the max planck society , and the higher education funding council for england . the sdss web site is @xmath61 . the sdss is managed by the astrophysical research consortium for the participating institutions . the participating institutions are the american museum of natural history , astrophysical institute potsdam , university of basel , university of cambridge , case western reserve university , university of chicago , drexel university , fermilab , the institute for advanced study , the japan participation group , johns hopkins university , the joint institute for nuclear astrophysics , the kavli institute for particle astrophysics and cosmology , the korean scientist group , the chinese academy of sciences ( lamost ) , los alamos national laboratory , the max planck institute for astronomy ( mpia ) , the max planck institute for astrophysics ( mpa ) , new mexico state university , ohio state university , university of pittsburgh , university of portsmouth , princeton university , the united states naval observatory , and the university of washington . this publication makes use of data products from the two micron all - sky survey , which is a joint project of the university of massachusetts and the infrared processing and analysis center / california institute of technology , funded by the national aeronautics and space administration and the national science foundation . this publication also makes use of data products from the wide - field infrared survey explorer , which is a joint project of the university of california , los angeles , and the jet propulsion laboratory / california institute of technology , funded by the national aeronautics and space administration .

the templates cover spectral types o5 through l3 , are binned by metallicity from -2.0 dex through + 1.0 dex and are separated into main sequence ( dwarf ) stars and giant stars . with recently developed m dwarf metallicity indicators , we identify trends in color space with metallicity and surface gravity , which will be useful for analyzing large data sets from upcoming missions like lsst . along with the templates , we are releasing a code for automatically ( and/or visually ) identifying the spectral type and metallicity of a star .

we present a library of empirical stellar spectra created using spectra from the sloan digital sky survey s baryon oscillation spectroscopic survey ( boss ) . the templates cover spectral types o5 through l3 , are binned by metallicity from -2.0 dex through + 1.0 dex and are separated into main sequence ( dwarf ) stars and giant stars . with recently developed m dwarf metallicity indicators , we are able to extend the metallicity bins down through the spectral subtype m8 , making this the first empirical library with this degree of temperature _ and _ metallicity coverage . the wavelength coverage for the templates is from 3650 through 10200 at a resolution better than r . using the templates , we identify trends in color space with metallicity and surface gravity , which will be useful for analyzing large data sets from upcoming missions like lsst . along with the templates , we are releasing a code for automatically ( and/or visually ) identifying the spectral type and metallicity of a star .

1205.5930

i

we are concerned with weakly nonlinear geometric optics for entropy solutions of the following hyperbolic system of conservation laws : @xmath2 where @xmath3 : @xmath4 is a smooth function . the jacobian matrix @xmath5 is diagonalizable at any point @xmath6 and has @xmath7 real eigenvalues such that any eigenvalue has constant multiplicity . without loss of generality , we assume that @xmath8 where @xmath9 , @xmath10 , and the corresponding left and right eigenvectors @xmath11 and @xmath12 satisfy @xmath13 here @xmath14 is the kronecker delta satisfying @xmath15 and @xmath16 when @xmath17 . when @xmath18 , the system in is strictly hyperbolic . in addition , we assume that each characteristic field is either genuinely nonlinear or linearly degenerate , that is , either of the following holds : @xmath19 a prototype of such hyperbolic systems is the full steady euler equations for supersonic ideal gases in @xmath20 with the following form for @xmath21 : @xmath22 where @xmath23 is the density , @xmath24 the fluid velocity , and @xmath25 the pressure . the notation @xmath26 denotes the tensor product of the vectors @xmath27 and @xmath28 . set @xmath29 . when @xmath30 , the vector @xmath31 can be expressed as a vector function @xmath32 of @xmath33 . then the system can be written into the form in with @xmath34 . by direct calculation , we find that the eigenvalues of this system are @xmath35 and the corresponding eigenvectors are @xmath36 , and @xmath37 . then @xmath38 \rr_{0j}\cdot\nabla\lambda_0\equiv0 \,\,\,\ , \qquad \mbox{for } \;\ ; j=1 , 2 . \end{array}\ ] ] thus , the two characteristic fields corresponding to @xmath39 are genuinely nonlinear , while the other two fields corresponding to @xmath40 are linearly degenerate . an asymptotic geometric optics expansion is of the following form : @xmath41 where @xmath42 is a constant background state in . by a formal derivation of the expansion of weakly nonlinear geometric optics for conservation laws ( _ cf . _ diperna - majda @xcite ) , the expansion is expected to be @xmath43 and the functions @xmath44 satisfy a decoupled system of scalar conservation laws : @xmath45 with the coefficients @xmath46 then the genuinely nonlinear condition from implies that @xmath47 which yields that equation is the inviscid burgers equation : @xmath48 while the linearly degenerate condition implies that @xmath49 which yields a linear equation @xmath50 we define @xmath51 then the much simpler function @xmath52 can be used to study the behavior of general entropy solutions of nonlinear hyperbolic system of conservation laws , provided that the convergence can be rigorously verified . an approach has been introduced in chen - christoforou - zhang @xcite , based on the results presented in bressan @xcite , to compare the solutions of two different systems , which requires that one of them is the standard riemann semigroup ( srs ) while the other is only a global entropy solution with bounded variation obtained by the front tracking method . let @xmath53 be a closed domain . a map @xmath54 is a * srs * generated by system if the following three conditions hold ( _ cf . _ @xcite ) : @xmath55 semigroup property : : for every @xmath56 and @xmath57 , @xmath58 @xmath55 lipschitz continuity : : there exist constants @xmath59 and @xmath60 such that , for all @xmath61 and @xmath62 @xmath63 @xmath55 consistency with the riemann solver : : for any piecewise constant initial data @xmath64 , there exists @xmath65 such that , for all @xmath66 $ ] , the trajectory @xmath67 coincides with the solution of the cauchy problem obtained by piecing together the standard solutions for the riemann problems determined by the jumps of @xmath68 . following @xcite , in this paper , the general entropy solution @xmath69 of the cauchy problem under consideration is the srs , which can be constructed by the front tracking method ( _ cf . _ @xcite ) , and the entropy solution for the corresponding asymptotic scalar equation is constructed by polygonal approximations , first introduced in dafermos @xcite , with initial data : @xmath70 we establish the @xmath71-estimate between @xmath69 and @xmath72 by using both the properties of the wave - front tracking algorithm and the standard error formula ( _ cf . _ @xcite ) : @xmath73 where @xmath74 is the lipschitz constant of the semigroup @xmath75 , and @xmath76 is any lipschitz continuous map defined on @xmath77 $ ] . one of our objectives here is to develop a new approach to provide a rigorous mathematical proof of the following theorem . [ thm : compacted initial data]*(main theorem ) . * let @xmath78 , and let @xmath79 be an arbitrary function of bounded variation with compact support . assume that each eigenvalue of the hyperbolic system in has constant multiplicity and its corresponding characteristic field is either genuinely nonlinear or linearly degenerate . consider an entropy solution @xmath80 of the cauchy problem , which is a srs , and the weakly nonlinear geometric optics expansion function @xmath81 defined by and . then there exists @xmath82 such that , for all @xmath83 and @xmath84 $ ] , @xmath85 for some @xmath86 independent of @xmath87 and @xmath88 . we remark here that this result allows the eigenvalues of the @xmath89 hyperbolic system in to have constant multiplicity and the corresponding characteristic fields to be linearly degenerate , which answers the open problem posed by majda in @xcite . in particular , for the @xmath89 system in , we obtain that the @xmath0estimate between the entropy solution and the geometric optics expansion function is bounded by @xmath1 that is _ independent of @xmath90_. the proof of theorem [ thm : compacted initial data ] is based on our following observation : for a genuinely nonlinear system with initial data of compact support , the waves of different families in the solution will be separated each other . this enables us to follow majda - rosaales @xcite and use the front tracking method . we introduce an auxiliary approximate function @xmath91 by adding higher order term of @xmath92 to as @xmath93 and its corresponding more accurate auxiliary approximate function : @xmath94 where @xmath95 means that the corresponding @xmath96th characteristic field is genuinely nonlinear , while @xmath97 means that the corresponding characteristic field is linearly degenerate and all @xmath98 together constitute the @xmath99-th characteristic field ; furthermore , @xmath100 is given in [ sec : scalar scheme ] and @xmath101 is defined in 5 . the novelty here is that the new correction terms are introduced to deal with the contact discontinuities . with this key observation , then our approach is to prove the @xmath71distance between this auxiliary function and the general entropy solution to system with the same initial data is @xmath102 , and finally to employ the @xmath71stability of solutions with respect to initial data to establish theorem [ thm : compacted initial data ] . the complete proof of theorem [ thm : compacted initial data ] will be given in [ sec : main thm ] and [ sec : compact support ] . this provides an alternative approach to deal with nonlinear geometric optics for hyperbolic systems of conservation laws in . as an example of further applications of this approach , we extend the result to the case when the initial data has non - compact support . [ thm : noncompact case ] let @xmath78 and @xmath103 . assume that each real eigenvalue of the hyperbolic system in has constant multiplicity and its corresponding characteristic field is either genuinely nonlinear or linearly degenerate . consider an entropy solution @xmath80 of the cauchy problem , which is the srs , and the weakly nonlinear geometric optics expansion @xmath81 defined by . then @xmath104 for related earlier results in this direction , we refer the reader to diperna - majda @xcite for an order of @xmath105 for the case of periodic initial data and the same estimate for initial data with compact support for @xmath106 genuinely nonlinear and strictly hyperbolic systems of conservation laws . for general strictly hyperbolic systems with some kind of periodic properties of the initial data for which the resonance phenomena occur , schochet @xcite proved the @xmath71-estimate of order @xmath107 ; and cheverry @xcite dealt with more general initial data and proved that , for all @xmath108 , @xmath109 where @xmath110 is the corresponding geometric optics expansion . both of their results allow the characteristic fields to be linearly degenerate , but require the hyperbolic system in to be strictly hyperbolic . we also refer the reader to chen - junca - rascke @xcite , cheverry @xcite , gus @xcite , hunter - majda - rosales @xcite , joly - mtivier - rauch @xcite , majda - rosales @xcite , and the references cited therein for related results . for classical results on the front tracking method and hyperbolic systems of conservation laws , see bressan @xcite and dafermos @xcite .

we present a new approach to analyze the validation of weakly nonlinear geometric optics for entropy solutions of nonlinear hyperbolic systems of conservation laws whose eigenvalues are allowed to have constant multiplicity and corresponding characteristic fields to be linearly degenerate . the approach is based on our careful construction of more accurate auxiliary approximation to weakly nonlinear geometric optics , the properties of wave front - tracking approximate solutions , the behavior of solutions to the approximate asymptotic equations , and the standard semigroup estimates . to illustrate this approach more clearly , we focus first on the cauchy problem for the hyperbolic systems with compact support initial data of small bounded variation and establish that theestimate between the entropy solution and the geometric optics expansion function is bounded by , _ independent of _ the time variable . this implies that the simpler geometric optics expansion functions can be employed to study the behavior of general entropy solutions to hyperbolic systems of conservation laws . finally , we extend the results to the case with non - compact support initial data of bounded variation .

we present a new approach to analyze the validation of weakly nonlinear geometric optics for entropy solutions of nonlinear hyperbolic systems of conservation laws whose eigenvalues are allowed to have constant multiplicity and corresponding characteristic fields to be linearly degenerate . the approach is based on our careful construction of more accurate auxiliary approximation to weakly nonlinear geometric optics , the properties of wave front - tracking approximate solutions , the behavior of solutions to the approximate asymptotic equations , and the standard semigroup estimates . to illustrate this approach more clearly , we focus first on the cauchy problem for the hyperbolic systems with compact support initial data of small bounded variation and establish that theestimate between the entropy solution and the geometric optics expansion function is bounded by , _ independent of _ the time variable . this implies that the simpler geometric optics expansion functions can be employed to study the behavior of general entropy solutions to hyperbolic systems of conservation laws . finally , we extend the results to the case with non - compact support initial data of bounded variation .

1208.0714

i

approximately half of the elements heavier than iron in the universe are produced via a series of @xmath12 neutron capture reactions and competing @xmath13-decays ( the @xmath9-process ) . during the @xmath9-process , the neutron number density is relatively low , of the order of 10@xmath14 n @xmath15 . when the flux reaches an unstable nucleus , it typically decays rather than capture another neutron and the @xmath9-process proceeds via the isotopes around the valley of @xmath13-stability ( e.g. , * ? ? ? * ) . the astrophysical sites of the @xmath9-process are core he and shell c burning in massive stars for the elements lighter than sr @xcite , and the `` he intershell '' of asymptotic giant branch ( agb ) stars for the elements between sr and bi @xcite . stars with initial masses lower than roughly 9 @xmath11 reach the agb phase in the final phases of their evolution , when both h and he have been exhausted in the core leaving c and o in electron degenerate conditions . production of nuclear energy occurs in the h and he shells , which are located between the core and the extended convective envelope and are separated by the thin he intershell layer . agb stars experience thermal pulses ( tps ) when the usually dormant he burning shell is suddenly activated . a large amount of energy is released , which drives convection in the he intershell . during tps the star expands and cools and the h burning shell is inactive . while he burning turns from the convective to the radiative regime , and eventually switches off , the convective envelope can penetrate the underlying he intershell and carry to the surface the products of he burning , in particular carbon and the elements heavier than iron made by the @xmath9-process . this mixing process is known as the `` third dredge - up '' ( tdu ) . after the tdu is ended , the star contracts and heats up again and h burning resumes until another tp occurs and the cycle is repeated . this sequence of events can occur from a few times to hundreds of times , depending on the stellar mass and the mass - loss rate . agb stars suffer from very strong stellar winds , which erode the envelope roughly within a million years and shed the newly synthesized material mixed to the surface by the tdu into the interstellar medium . eventually , the c - o degenerate core is left as a cooling white dwarf ( see * ? ? ? * for a review on agb stars ) . according to the current standard model @xcite , some protons must diffuse from the convective envelope into the he intershell at the end of each tdu in order to produce enough @xmath4c to account for the observed abundances of the @xmath9-process elements at the surface of agb stars ( see also * ? ? ? * ) . a thin layer is then produced , known as the @xmath4c `` pocket '' , which is rich in @xmath4c made via @xmath16c(@xmath17,@xmath18)@xmath4n(@xmath19)@xmath4c . when in this region the temperature reaches about @xmath20 k , the @xmath4c(@xmath0,@xmath7)@xmath8o reaction is activated and generates neutrons that trigger the @xmath9-process @xcite . considerable effort has been devoted to the direct measurement of the @xmath4c(@xmath0,@xmath7)@xmath8o cross section @xcite . these measurements have been performed at energies down to 270 kev , whereas the gamow window is at 190 @xmath21 40 kev , corresponding to a temperature of 100 mk . since this energy is far below the coulomb barrier , the reaction cross section is extremely small and direct measurement is sensitively limited by background signals and very difficult to perform in laboratories on the earth s surface . while a measurement has been proposed at the underground laboratory of luna @xcite , at present , the experimental cross sections have to be extrapolated below 270 kev . a microscopic cluster model analysis of the @xmath4c(@xmath0,@xmath7)@xmath8o and @xmath4c(@xmath0,@xmath0 ) reactions by @xcite suggested that this extrapolation is critically affected by the 1/2@xmath2 subthreshold resonance in @xmath3o ( @xmath22 = 6.356 mev , just 3 kev below the @xmath0-decay threshold ) . the contribution from this resonance depends strongly on the @xmath0-width of the 1/2@xmath2 state in @xmath3o , which can be derived from the spectroscopic factor ( @xmath1 ) or the asymptotic normalization coefficient ( anc ) of @xmath0-cluster in this state . the @xmath1 and the anc can be determined from the angular distribution of the direct @xmath0-transfer reaction using distorted wave born approximation ( dwba ) or coupled reaction channels ( crc ) analysis . although three indirect measurements via the ( @xmath23li,@xmath24 ) or the ( @xmath6li,@xmath25 ) system have been performed by @xcite , @xcite , and @xcite to study the @xmath1 or the anc of the 1/2@xmath2 state , there still exists a significant discrepancy of up to a factor of @xmath1030 in the derived @xmath1 and anc . therefore , it is interesting to perform a new measurement of the @xmath1 and the anc via an independent transfer reaction . in addition , it is necessary to understand the impact of the different resulting @xmath4c(@xmath0,@xmath7)@xmath8o rates on the @xmath9-process nucleosynthesis in agb stars . in this paper we determine a new stellar rate of the @xmath4c(@xmath0,@xmath7)@xmath8o reaction and incorporate it in calculations of the @xmath9-process nucleosynthesis in agb stars . first , we measure the angular distribution of the @xmath4c(@xmath5b,@xmath6li)@xmath3o reaction to determine the @xmath1 and the anc for the 1/2@xmath2 state in @xmath3o . using this experimental anc we derive the @xmath0-width for the 1/2@xmath2 subthreshold resonance , which is currently the most uncertain parameter for determining the @xmath4c(@xmath0,@xmath7)@xmath8o rate . finally , we use the new rate and different rates available in the literature as input for simulations of agb stars to study their influence on the abundance of some selected @xmath9-process elements and isotopic ratios .

this is believed to have a strong effect on the rate of thec(,)o reaction , the main neutron source for _ slow _ neutron captures ( the-process ) in asymptotic giant branch ( agb ) stars . we use the new rate and different rates available in the literature as input in simulations of agb stars to study their influence on the abundances of selected-process elements and isotopic ratios .

we present a new measurement of the-spectroscopic factor ( ) and the asymptotic normalization coefficient ( anc ) for the 6.356 mev 1/2 subthreshold state ofo through thec(b,li)o transfer reaction and we determine the-width of this state . this is believed to have a strong effect on the rate of thec(,)o reaction , the main neutron source for _ slow _ neutron captures ( the-process ) in asymptotic giant branch ( agb ) stars . based on the new width we derive the astrophysical s - factor and the stellar rate of thec(,)o reaction . at a temperature of 100 mk our rate is roughly two times larger than that by and two times smaller than that recommended by the nacre compilation . we use the new rate and different rates available in the literature as input in simulations of agb stars to study their influence on the abundances of selected-process elements and isotopic ratios . there are no changes in the final results using the different rates for thec(,)o reaction when thec burns completely in radiative conditions . when thec burns in convective conditions , as in stars of initial mass lower than and in post - agb stars , some changes are to be expected , e.g. , of up to 25% for pb in our models . these variations will have to be carefully analyzed when more accurate stellar mixing models and more precise observational constraints are available .

1208.0714

i

we determined the stellar rate of the @xmath4c(@xmath0,@xmath7)@xmath8o reaction and incorporated the new reaction rate in calculations of the @xmath9-process nucleosynthesis in agb stars . the @xmath1 and anc for the 6.356 mev 1/2@xmath2 subthreshold state in @xmath3o were obtained from the measurement of the @xmath4c(@xmath5b,@xmath6li)@xmath3o angular distribution . this provided an independent examination to shed some light on the existing discrepancies in the @xmath1 and anc values derived from different authors . based on the measured anc , we extracted the @xmath0-width of the 1/2@xmath2 state in @xmath3o , which is currently the most uncertain parameter for determining the @xmath4c(@xmath0,@xmath7)@xmath8o reaction rate . by using the present @xmath0-width and considering the properties of @xmath3o states up to 8.342 mev as well as their interferences , we derived the astrophysical s - factor and the stellar rate of the @xmath4c(@xmath0,@xmath7)@xmath8o reaction . at a temperature of 100 mk the new rate is roughly two times larger than the cf88 value and two times smaller than that recommended by nacre ( see fig . [ fig5 ] ) . verification of the present result using other independent techniques is desirable , e.g. , the trojan horse approach @xcite , and the isospin symmetry approach based on a measurement of the 1/2@xmath2 6.560 mev state in @xmath3f @xcite . in addition , an extension of the experimental data of @xmath4c(@xmath0,@xmath7)@xmath8o toward lower energies is highly desirable , which can probably only be performed in an underground laboratory , e.g. , luna ( see * ? ? ? * ) . we incorporated different @xmath4c(@xmath0,@xmath7)@xmath8o reaction rates in calculations of the @xmath9-process nucleosynthesis in agb stars and found that : ( 1 ) if @xmath4c burns completely in radiative conditions during the interpulse phase ( as for stars of initial mass greater than @xmath102 @xmath11 ) , there is no change in the final results . ( 2 ) if some @xmath4c burns instead inside the convective tps ( for stars of initial mass lower than @xmath102 @xmath11 ) , we find changes of up to 25% in the @xmath9-process results , particularly for pb . there are model uncertainties related to the result of point ( 2 ) : a ) when @xmath4c burning in the tps is due to incomplete burning of the @xmath4c during the interpulse period , the exact stellar mass and metallicity range where incomplete burning of the @xmath4c during the interpulse period occurs , as well as tp numbers , and the exact amount of @xmath4c ingested , all depend sensitively on the temperature and density in the @xmath4c pocket , on the interpulse period , and on the details of the inclusion of the @xmath4c pocket . b ) when @xmath4c burning in the tps is due to ingestion of protons directly inside the tp ( as in low - mass and low - metallicity stars , as well as in post - agb stars experiencing a late tp , see * ? ? ? * ) , the amount of @xmath4c and neutrons produced strongly depends on the physical and numerical treatment of the mixing scheme adopted , which is at present uncertain . due to these model uncertainties together with the fact that the stellar observations have relatively large error bars , it is presently not possible to conclude if the new rate of the @xmath4c(@xmath0,@xmath7)@xmath8o reaction provides the best match to the available observational constraints . this may be however possible in the future , when development of recent 3d hydrodynamical models of the proton ingestion episodes @xcite will allow a better understanding of neutron production and the @xmath9-process inside tps to be compared to the composition of stellar observations and stardust grains . thanks natasha timofeyuk for helpful discussions on dwba calculation and isospin symmetry in mirror @xmath0-decays , and thanks grigory rogachev for useful discussions on the source of the discrepancy between their results , and thanks grigory rogachev and farouz hammache for providing him with their reaction rates in tabular form . m.l . acknowledges the support of the arc via a future fellowship and of monash university via a monash fellowship . we thank the anonymous referee for many helpful comments and suggestions . we acknowledge the staff of tandem accelerator for the smooth operation of the machine . this work was supported by the national natural science foundation of china under grant nos . 11021504 , 10735100 and 11035001 , the national basic research program of china ( new physics and technology at the limits of nuclear stability ) , the outstanding tutors for doctoral dissertations of s&t project in beijing under grant no . + angulo , c. , arnould , m. , rayet , m. et al . 1999 , , 656 , 3 bair , j. k. , & haas , f. x. 1973 , , 7 , 1356 burbidge , e. m. , burbidge , g. r. , fowler , w. a. , & hoyle , f. 1957 , rev . phys . , 29 , 547 busso , m. , gallino , r. , & wasserburg g. j. 1999 , , 37 , 239 busso , m. , gallino , r. , lambert , d. l. , travaglio , c. , & smith , v. v. 2001 , , 557 , 802 brune , c. r. , licot , i. , & kavanagh , r. w. 1993 , , 48 , 3119 caughlan , g. , & fowler , w. 1988 , at . data nucl . data tables , 40 , 283 cook , j. , stephens , m. n. , & kemper , k. w. 1987 , , 466 , 168 costantini , h. , formicola , a. , imbriani , g. , junker , m. , rolfs , c. , & strieder , f. 2009 , rep . 72 , 086301 cristallo , s. , straniero , o. , gallino , r. , piersanti , l. , domnguez , i. , & lederer , m. t. 2009a , , 696 , 797 cristallo , s. , piersanti , l. , straniero , o. , gallino , r. , domnguez , i. , & kppeler , f. 2009b , , 26 , 139 davids , c. n. 1968 , , 110 , 619 denker , a. , drotleff , h. w. , groe , m. , knee , h. , kunz , r. , mayer , a. , seidel , r. , soin , m. , whr , a. , wolf , g. , & hammer , j. w. 1995 , in proc . astrophys . , nuclei in the cosmos iii , 327 , 255 descouvemont , p. 1987 , , 36 , 2206 drotleff , h. w. , denker , a. , knee , h. , soin , m. , wolf , g. , hammer , j. w. , greife , u. , rolfs , c. , & trautvetter , h. p. 1993 , , 414 , 735 gallino , r. , busso , m. , picchio , g. , raiteri , c. m. , & renzini , a. 1988 , , 334 , 45 gallino , r. , arlandini , c. , busso , m. , lugaro , m. , travaglio , c. , straniero , o. , chieffi , a. , & limongi , m. 1998 , , 497 , 388 goriely , s. , & mowlavi , n. 2000 , , 362 , 599 goriely , s. , & siess , l. 2004 , , 421 , l25 harissopulos , s. , becker , h. w. , hammer , j. w. , lagoyannis , a. , rolfs , c. , & strieder , f. 2005 , , 72 , 062801 heil , m. , detwiler , r. , azuma , r. e. , couture , a. , daly , j. , grres , j. , kppeler , f. , reifarth , r. , & tischhauser , p. 2008 , , 78 , 025803 herwig , f. 2004 , , 605 , 425 herwig , f. 2005 , , 43 , 435 herwig , f. 2011 , , 727 , 89 hollowell , d. , & iben , i. , jr . 1988 , , 333 , 25 iliadis , c. 2007 , nuclear physics of stars ( weinheim : wiley - 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flam ( gif - sur - yvette : editions frontire ) , 525 thompson , i. j. 1988 , comput . , 7 , 167 tilley , d. r. , weller , h. r. , & cheves , c. m. 1993 , , 565 , 1 timofeyuk , n. k. , descouvemont , p. , & johnson , r. c. 2007 , , 75 , 034302 van raai , m. , lugaro , m. , karakas , a. i. , garcia - hernandez , d. a. , yong , d. 2012 , , accepted vassiliadis , e. , & wood , p. r. 1993 , , 413 , 641 verchovsky , a. b. 2004 , , 607 , 611 cccccccc channel & @xmath116 & @xmath117 & @xmath118 & @xmath119 & @xmath120 & @xmath121 & @xmath122 + @xmath5b+@xmath4c & 50.0 & 182.64 & 0.788 & 0.740 & 8.193 & 1.250 & 0.740 + @xmath6li+@xmath3o & 26.0 & 114.20 & 0.737 & 0.719 & 34.602 & 0.997 & 0.764 + @xmath6li+@xmath4c & 31.8 & 159.00 & 0.630 & 0.810 & 8.160 & 1.330 & 0.780 + ccccc reference & transfer system & incident energy&@xmath1 & @xmath61 + & & ( mev ) & & ( @xmath62 ) + @xcite & @xmath4c(@xmath23li,@xmath24)&60&0.011 & + @xcite & @xmath4c(@xmath23li,@xmath24)&60&0.36@xmath450.40 & + @xcite & @xmath23li(@xmath4c,@xmath24)&8.0 and 8.5&&0.89 @xmath21 0.23 + @xcite & @xmath4c(@xmath6li,@xmath25)&28 and 34&0.29 @xmath21 0.11&4.5 @xmath21 2.2 + present work & @xmath4c(@xmath5b,@xmath6li)&50&0.37 @xmath21 0.12&4.0 @xmath21 1.1 + ccccccc level&@xmath22 ( kev ) & @xmath90 ( kev ) & @xmath123 & @xmath124 ( kev ) & @xmath125 ( kev)&@xmath85 ( kev ) + 1&6356 & @xmath453 & 1/2@xmath2 & 124 & & 12.7 + 2&7165&806&5/2@xmath49&1.38&0.0033 & + 3&7201&842&3/2@xmath2&340&0.08 & + 4&7378&1019&5/2@xmath2&0.64&0.01 & + 5&7381&1022&5/2@xmath49&0.96&0.003 & + 6&7558&1199&3/2@xmath49&500&0.08 & + 7&7688&1329&7/2@xmath49&13&0.01 & + 8&7956&1597&1/2@xmath2&84&6.7 & + 9&7991&1632&1/2@xmath49&250&16 & + 10&8058&1699&3/2@xmath2&71&15 & + 11&8200&1841&3/2@xmath49&48&4.0 & + 12&8342&1983&1/2@xmath2&8.1&2.2 & + .[tab4 ] numerical values of the present @xmath4c(@xmath0,@xmath7)@xmath8o rates ( @xmath126/mol / s ) with the adopted value , upper and lower limits for the 0.04@xmath453.0 gk temperature range and the coefficients @xmath97 in eq . [ eq8 ] for these three rates . the overall fitting errors are all less than 7% at temperatures from 0.04 to 10.0 gk . [ cols="^,^,^,^,^,^,^,^ " , ]

we present a new measurement of the-spectroscopic factor ( ) and the asymptotic normalization coefficient ( anc ) for the 6.356 mev 1/2 subthreshold state ofo through thec(b,li)o transfer reaction and we determine the-width of this state . based on the new width we derive the astrophysical s - factor and the stellar rate of thec(,)o reaction . at a temperature of 100 mk our rate is roughly two times larger than that by and two times smaller than that recommended by the nacre compilation . there are no changes in the final results using the different rates for thec(,)o reaction when thec burns completely in radiative conditions . when thec burns in convective conditions , as in stars of initial mass lower than and in post - agb stars , some changes are to be expected , e.g. , of up to 25% for pb in our models . these variations will have to be carefully analyzed when more accurate stellar mixing models and more precise observational constraints are available .

we present a new measurement of the-spectroscopic factor ( ) and the asymptotic normalization coefficient ( anc ) for the 6.356 mev 1/2 subthreshold state ofo through thec(b,li)o transfer reaction and we determine the-width of this state . this is believed to have a strong effect on the rate of thec(,)o reaction , the main neutron source for _ slow _ neutron captures ( the-process ) in asymptotic giant branch ( agb ) stars . based on the new width we derive the astrophysical s - factor and the stellar rate of thec(,)o reaction . at a temperature of 100 mk our rate is roughly two times larger than that by and two times smaller than that recommended by the nacre compilation . we use the new rate and different rates available in the literature as input in simulations of agb stars to study their influence on the abundances of selected-process elements and isotopic ratios . there are no changes in the final results using the different rates for thec(,)o reaction when thec burns completely in radiative conditions . when thec burns in convective conditions , as in stars of initial mass lower than and in post - agb stars , some changes are to be expected , e.g. , of up to 25% for pb in our models . these variations will have to be carefully analyzed when more accurate stellar mixing models and more precise observational constraints are available .

0810.2119

i

we have presented mass models for the nearby dwarf galaxies , ic 2574 and ngc 2366 , derived using the high - resolution data from things . these high - resolution data do not suffer from beam smearing , have a well - defined dynamical center and enable us to examine in detail the dark matter distribution of these galaxies . to minimize the effects of random non - circular motions on the derived kinematics of a galaxy , we developed a new gaussian decomposition method and used this to construct a `` bulk '' velocity field of ic 2574 and ngc 2366 , showing the underlying undisturbed rotation . the random , non - circular motions of ic 2574 and ngc 2366 , visible as distortions in the velocity contours of the traditional iwm velocity fields , were largely removed in the newly constructed bulk velocity fields . comparing the hi rotation curves derived from the bulk and iwm velocity fields , we find that the rotation velocities derived from the iwm velocity fields are significantly lower than those from the bulk velocity fields . in addition , non - circular motions of ngc 2366 are likely to be responsible for the declining rotation velocities derived from the iwm velocity fields in the outer parts . combining optical and sings 3.6 @xmath1 m data , we quantify the dynamical contribution of the stellar component to the total kinematics . for this we compute @xmath11 values based on the bruzual and charlot ( 2003 ) population synthesis models for the 3.6 @xmath1 m and 4.5 @xmath1 m bands . we have fitted nfw and pseudo - isothermal dark matter halos to the derived rotation curves , taking into account the contributions due to stars and gas . we found that the pseudo - isothermal halo provides a better fit to the observations than the nfw halo . we use the derived mass density profile to determine the value of the inner slope . the measured slopes are @xmath148 for ic 2574 and @xmath149 for ngc 2366 , compared to the nfw model which predicts @xmath152 . the dark matter distributions of ic 2574 and ngc 2366 are well described by the pseudo - isothermal model ( @xmath153 ) with a sizeable central constant - density core . these results are not affected by systematic effects due to lack of resolution or pointing offsets , take into account the effects of non - circular motions and use a well - constrained model for @xmath11 . the work of wjgdb is based upon research supported by the south african research chairs initiative of the department of science and technology and national research foundation . eb gratefully acknowledges financial support through an eu marie curie international reintegration grant ( contract no . mirg - ct-6 - 2005 - 013556 ) . this research has made use of the nasa / ipac extragalactic database ( ned ) which is operated by the jet propulsion laboratory , california institute of technology , under contract with the national aeronautics and space administration . this publication makes use of data products from the two micron all 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brinks , e. , & klein , u. 1998 , , 502 , 143 walter , f. , brinks , e. , de blok , w. j. g. , bigiel , f. , thornley , m. , & kennicutt , r. c. 2005 , aas , 207 , 6409 walter , f. et al . 2007 , , 661 , 102 walter , f. , brinks , e. , de blok , w. j. g. , bigiel , f. , kennicutt , r. c. , & thornley , m. 2008 , , submitted weldrake , d. t. f. , de blok , w. j. g. , & walter , f. 2003 , , 340 , 12 whiting , a. b. 1999 , the stellar content of local group galaxies , iau symposium 192 , 420 cccccccc [ ml_param ] 3.6 @xmath1 m & & @xmath154 & & & & 0.92 & + 4.5 @xmath1 m & & @xmath155 & & & & 0.91 & + & & & + color & @xmath77 & @xmath78 & @xmath156 & & @xmath77 & @xmath78 & @xmath156 + & ( 3 ) & ( 4 ) & ( 5 ) & & ( 6 ) & ( 7 ) & ( 8) + @xmath157 & @xmath158 & 0.60 & 0.44 & & @xmath159 & 0.72 & 0.33 + @xmath160 & @xmath161 & 0.42 & & & & & + @lrclccccrc & & & + + & & & & & & & & & + & & & & & & & & & + min . disk & 0.00 & @xmath162 & 674.6 @xmath163 18.3 & 2.88 & & 0.00 & @xmath162 & 1213.6 @xmath163 ... & 3.39 + min . disk+gas & 0.00 & @xmath162 & 524.3 @xmath163 51.7 & 1.65 & & 0.00 & @xmath162 & 1005.5 @xmath163 ... & 2.32 + max . disk & 0.93 & @xmath162 & 634.4 @xmath163 ... & 2.33 & & 0.93 & @xmath162 & 353.8 @xmath163 ... & 1.63 + model @xmath164 disk & 0.44 & @xmath162 & 873.9 @xmath163 ... & 1.81 & & 0.44 & @xmath162 & 700.5 @xmath163 ... & 1.96 + @xmath165disk & @xmath166 & @xmath162 & 1107.7 @xmath163 ... & 1.66 & & & & & + + & & & + + & & & & & & & & & + & & & & & & & & & + min . disk & 0.00 & 5.77 @xmath163 0.16 & 7.8 @xmath163 0.2 & 0.25 & & 0.00 & 5.69 @xmath163 0.35 & 7.8 @xmath163 0.3 & 0.26 + min . disk+gas & 0.00 & 4.61 @xmath163 0.12 & 7.6 @xmath163 0.2 & 0.16 & & 0.00 & 3.88 @xmath163 0.16 & 8.7 @xmath163 0.3 & 0.13 + max . disk & 0.93 & 27.52 @xmath163 10.22 & 1.8 @xmath163 0.1 & 0.30 & & 0.93 & @xmath167 & 1.7 @xmath163 0.9 & 0.39 + model @xmath164 disk & 0.44 & 7.23 @xmath163 0.30 & 4.1 @xmath163 0.1 & 0.17 & & 0.44 & 5.87 @xmath163 0.55 & 4.5 @xmath163 0.3 & 0.19 + @xmath165disk & 0.10 & 4.99 @xmath163 0.34 & 6.7 @xmath163 0.7 & 0.16 & & & & + + * note.@xmath168 * * ( 1)(10 ) : * the stellar mass - to - light ratio @xmath11 assumptions . `` model @xmath85 disk '' uses the values derived from the population synthesis models in section 4.2 . @xmath165 has @xmath85 as a free parameter . * ( 2)(6)(11)(15 ) : * average @xmath11 in the 3.6 @xmath1 m band ( @xmath80/@xmath169 ) . * ( 3)(7 ) : * concentration parameter c of nfw halo model ( nfw 1996 , 1997 ) . * ( 4)(8 ) : * the rotation velocity ( @xmath10)at radius @xmath124 where the density constrast exceeds 200 ( navarro et al . 1996 ) . * ( 5)(9)(14)(18 ) : * reduced @xmath170 value . * ( 12)(16 ) : * fitted core - radius of pseudo - isothermal halo model ( kpc ) . * ( 13)(17 ) : * fitted core - density of pseudo - isothermal halo model ( @xmath171 @xmath172 ) . * ( @xmath167 ) : * blank due to unphysically large value or not well - constrained uncertainties . @lrclccccrc & & & + + & & & & & & & & & + & & & & & & & & & + min . disk & 0.00 & @xmath162 & 901.5 @xmath163 478.4 & 1.72 & & 0.00 & @xmath162 & 1600.5 @xmath163 @xmath167 & 2.35 + min . disk+gas & 0.00 & @xmath162 & 727.8 @xmath163 @xmath167 & 1.08 & & 0.00 & @xmath162 & 1136.6 @xmath163 @xmath167 & 1.48 + max . disk & 0.88 & @xmath162 & 936.1 @xmath163 @xmath167 & 0.89 & & 0.88 & @xmath162 & 954.8 @xmath163 @xmath167 & 1.26 + model @xmath164 disk & 0.33 & @xmath162 & 630.7 @xmath163 @xmath167 & 0.98 & & 0.33 & @xmath162 & 1143.6 @xmath163 @xmath167 & 1.37 + @xmath165 disk & 1.15 & @xmath162 & 665.7 @xmath163 @xmath167 & 1.26 & & & & & + + & & & + + & & & & & & & & & + & & & & & & & & & + min . disk & 0.00 & 1.47 @xmath163 0.06 & 44.6 @xmath163 2.2 & 0.16 & & 0.00 & 1.49 @xmath163 0.07 & 44.1 @xmath163 2.6 & 0.21 + min . disk+gas & 0.00 & 1.25 @xmath163 0.05 & 43.8 @xmath163 2.4 & 0.13 & & 0.00 & 1.25 @xmath163 0.06 & 43.7 @xmath163 2.8 & 0.18 + max . disk & 0.88 & 1.61 @xmath163 0.15 & 21.8 @xmath163 2.5 & 0.25 & & 0.88 & 1.62 @xmath163 0.18 & 21.8 @xmath163 3.0 & 0.34 + model @xmath164 disk & 0.33 & 1.36 @xmath163 0.07 & 34.8 @xmath163 2.4 & 0.17 & & 0.33 & 1.36 @xmath163 0.09 & 34.7 @xmath163 2.9 & 0.23 + @xmath165 disk & @xmath173 & 0.98 @xmath163 0.05 & 87.1 @xmath163 14.0 & 0.14 & & & & + + * note.@xmath168 * * ( 1)(10 ) : * the stellar mass - to - light ratio @xmath11 assumptions . `` model @xmath85 disk '' uses the values derived from the population synthesis models in section 4.2 . @xmath165 has @xmath85 as a free parameter . * ( 2)(6)(11)(15 ) : * average @xmath11 in the 3.6 @xmath1 m band ( @xmath80/@xmath169 ) . * ( 3)(7 ) : * concentration parameter c of nfw halo model ( nfw 1996 , 1997 ) . * ( 4)(8 ) : * the rotation velocity ( @xmath10)at radius @xmath124 where the density constrast exceeds 200 ( navarro et al . * ( 5)(9)(14)(18 ) : * reduced @xmath170 value . * ( 12)(16 ) : * fitted core - radius of pseudo - isothermal halo model ( kpc ) . * ( 13)(17 ) : * fitted core - density of pseudo - isothermal halo model ( @xmath171 @xmath172 ) . * ( @xmath167 ) : * blank due to unphysically large value or not well - constrained uncertainties .

the bulk velocity field rotation curves are significantly less affected by non - circular motions and constrain the dark matter distribution in our galaxies , allowing us to address the discrepancy between the inferred and predicted dark matter distribution in galaxies ( the `` cusp / core '' problem ) . _ # 1 # 1#1

we present a new method to remove the impact of random and small - scale non - circular motions from hi velocity fields in ( dwarf ) galaxies in order to better constrain the dark matter properties for these objects . this method extracts the circularly rotating velocity components from the hi data cube and condenses them into a so - called bulk velocity field . we derive high - resolution ( kpc ) rotation curves of ic 2574 and ngc 2366 based on bulk velocity fields derived from the hi nearby galaxy survey ( things ) obtained at the vla . we compare the bulk velocity field rotation curves with those derived from the traditional intensity - weighted mean velocity fields and find significant differences . the bulk velocity field rotation curves are significantly less affected by non - circular motions and constrain the dark matter distribution in our galaxies , allowing us to address the discrepancy between the inferred and predicted dark matter distribution in galaxies ( the `` cusp / core '' problem ) . _ spitzer _ infrared nearby galaxies survey ( sings ) 3.6 m data , which are largely unaffected by dust in these systems , as well as ancillary optical information , are used to separate the contribution of the baryons from the total matter content . using stellar population synthesis models , assuming various sets of metallicity and star formation histories , we compute stellar mass - to - light ratios for the 3.6 m and 4.5 m bands . using our predicted value for the 3.6 m stellar mass - to - light ratio , we find that the observed dark matter distributions of ic 2574 and ngc 2366 are inconsistent with the cuspy dark matter halo predicted by cold dark matter models , even after corrections for non - circular motions . this result also holds for other assumptions about the stellar mass - to - light ratio . the distribution of dark matter within our sample galaxies is best described by models with a kpc - sized constant - density core . # 1 # 1#1

astro-ph0004391

c

we present a new code which is designed to derive a sed for an arbitrary spatial distribution of stellar and gaseous components for a dusty starburst galaxy . by using this code , we can calculate seds based on numerical simulations that can analyze simultaneously dynamical and chemical evolution , structural and kinematical properties , morphology , star formation history , and transfer of metals and dust in interstellar medium for a starburst galaxy . accordingly , we can investigate variously different properties of starburst galaxies , such as effects of dynamical evolution on galactic seds , physical correlations between morphology and seds , photometric evolution from uv to submillimeter wavelength , two dimensional distribution of @xmath118 , and dependence of seds on line - of - site of an observer . thanks to this code , we can furthermore try to clarify the origin of possible candidates of starburst galaxies , such as low @xmath1 ulirgs ( e.g. , sanders et al . 1988 ; sanders & mirabel 1996 ) , intermediate z ones ( e.g. , tran et al . 1999 ) , faint scuba sources ( smail , ivison , & blain 1997 ; barger et al . 1998 ; hughes et al . 1998 ; smail et al . 1998 ; ivison et al . 1999 ; lilly et al . 1999 ) , eros ( elston , rieke , & rieke 1988 ; dey et al . 1999 ; smail et al . 1999 ) , optically faint radii sources detected by vla ( e.g. , richards et al . 1999 ) , lyman - break galaxies ( steidel et al . 1996 ; lowenthal et al . 1997 ) , and emission line galaxies ( e.g. , mannucci et al . 1998 ) . by using a new code developed in the present study , we try to answer the following seven questions in our forthcoming papers : ( 1 ) when and how a gas - rich major galaxy merger becomes an ulirg during the dynamical evolution of the merger ? ( 2 ) how high z faint scuba sources with dusty starburst form and evolve ? ( 3 ) what are physical conditions for high z dusty galaxies to become eros ? ( 4 ) are there any evolutionary links between high z possible dusty starburst galaxies , such as faint scuba sources , eros , optically faint radio sources recently detected by vla , emission line galaxies , and lyman - break ones ? ( 5 ) when does a forming disk galaxy show the strongest submillimeter flux ? ( 6 ) what physical processes can determine the shapes of seds observed in lyman - break galaxies ? ( 7 ) how dusty interstellar gas affects apparent morphology of intermediate and high @xmath1 dusty galaxies ? although this code has some disadvantages in deriving very precise seds of dusty starburst galaxies , we believe that this code enables us to grasp some essential ingredients of physical processes related to galaxy formation with starburst at low and high z universe . we are grateful for the referee g. d. bothun for giving us valuable comments and suggestions that greatly improve our paper . y.s . thank to the japan society for promotion of science ( jsps ) research fellowships for young scientist .

we present a new numerical code which is designed to derive a spectral energy distribution ( sed ) for an arbitrary spatial distribution of stellar and gaseous components in a dusty starburst galaxy . as an example , we demonstrate when and how a major galaxy merger with dusty starburst becomes an ultra - luminous infrared galaxy owing to strong internal dust extinction .

we present a new numerical code which is designed to derive a spectral energy distribution ( sed ) for an arbitrary spatial distribution of stellar and gaseous components in a dusty starburst galaxy . we apply a ray tracing method to numerical simulations and thereby estimate extinction and reemission of stellar light by dusty gas in an explicitly self - consistent manner . by using this code , we can investigate simultaneously dynamical and photometric evolution of a dusty galaxy based on stellar and gaseous dynamical simulations . as an example , we demonstrate when and how a major galaxy merger with dusty starburst becomes an ultra - luminous infrared galaxy owing to strong internal dust extinction . we furthermore discuss advantages and disadvantages of the present new code in clarifying the nature and the origin of low and high redshift dusty starburst galaxies .

1105.5683

i

the magnetohydrodynamics ( mhd ) approximation has some interesting properties , for example , the flux freezing and magnetic pressure ; the former can be used for the collimation of the jet , and the latter for the acceleration of the plasma . thus , the magnetic field is considered an essential ingredient for many astrophysical phenomena . in particular , many observations indicate that most of the high energy phenomena in astrophysics are related to the strongly magnetized relativistic plasma around some compact objects , for example , agn @xcite , relativistic jet @xcite , pulsar wind @xcite , gamma - ray bursts @xcite , and so on . since it is extremely difficult to solve the relativistic mhd ( rmhd ) equations analytically , the theoretical investigations in fully nonlinear regimes are mainly based on the numerical simulations @xcite . most of these studies approximates the plasma as the ideal rmhd fluid . one reason for this is that the ideal rmhd is an excellent approximation of high energy phenomena for ordinary parameters . however , when one considers extreme phenomena , such as the neutron star mergers , or the central engines of grb , the electrical conductivity can be small , and highly resistive regions may appear . in addition , when one considers the magnetic reconnection , the resistivity plays an essential role in this phenomenon . magnetic reconnection is one of the most important phenomena , since it is highly dynamic , and it changes magnetic field energy into fluid energy @xcite . though numerical results of ideal rmhd exhibit magnetic reconnection , this originates in the purely numerical resistivity , and this is unphysical . for this reason , using resistive rmhd is important for the understanding of reconnection and related phenomena . in order to consider ohmic dissipation , one only has to take into account an additional term @xmath0 in the induction equation of non - relativistic mhd . however , similar to other non - relativistic dissipation , this induction equation is parabolic and it is well - known that this equation is acausal . as a result , if one takes into account ohmic dissipation in a relativistic mhd in a similar way , the equation inevitably includes unphysical exponential growing modes , and unstable for small perturbations similar to other dissipation @xcite . this unphysical divergence results from the fact that one neglects the time derivative of the electric field in the induction equation with ohmic dissipation . for this reason , when one takes into account the ohmic dissipation , one has to consider the time evolution of the electric field , that is , one has to deal with the relativistic electromagnetic hydrodynamic equation . this equation is a telegrapher equation , and satisfies the causality . in this paper , we present a new numerical scheme for the resistive rmhd . there are several examples of pioneering work for resistive rmhd , for example , komissarov ( 2007 , hereafter k07 ) proposed numerical method that solves hyperbolic fluxes by using the harten - lax - van leer ( hll ) prescription , and damping of the electric field by ohmic dissipation that is very stiff by using strang - splitting techniques ; palenzuela et al . ( 2009 , hereafter p09 ) proposed a numerical method that solves hyperbolic fluxes by local lax - friedrichs approximate riemann solver , and the stiff part by using implicit - explicit ( imex ) runge kutta methods . however , these methods use light velocity as the characteristic velocity , and their numerical solutions are diffusive when one considers problems whose characteristic velocity is much lower than light velocity . this indicates that their numerical solutions are diffusive in many important high plasma @xmath1 dynamics , and also their solutions become highly diffusive when the characteristic velocity of phenomena is much lower than light velocity . in particular , when one solves the dynamics of the accretion disk around a black hole with a relativistic jet , one has to use relativistic resistive mhd code that can solve both highly relativistic and non - relativistic dynamics with resistivity for the following three reasons : ( 1 ) the saturation of the magnetorotational instability ( mri ) depends on the resistivity ; ( 2 ) the dynamics of an accretion disk are not ordinarily relativistic , especially , the dynamics of the mri is sub - alfvnic ; ( 3 ) the dynamics of the jet are highly relativistic . for these reasons , previous schemes are diffusive in such phenomena , and we need more accurate numerical schemes . we are developing a new numerical scheme capable of accurately solving problems whose characteristic velocity is quite different from light velocity . in this scheme , we obtain numerical flux of fluid by using sound velocity as the characteristic velocity , and numerical flux of electromagnetic field by using appropriate characteristic velocities of rmhd . this enables us to obtain accurate numerical results when we consider problems whose characteristic velocity is much lower than light velocity . in addition , p09 pointed out that the strang - splitting method used in the komissarov method is unstable when applied to discontinuous flows with large conductivities . however , we find that this problem is not related to the strang - splitting method , but the evolution of electric field @xmath2 during the primitive recovery , that is introduced in the method by p09 . by considering this procedure , we can apply the strang - splitting method to discontinuous flows with large conductivities . this paper is organized as follows . in section [ sec : sec2 ] , the basic equations of resistive rmhd are presented . in section [ sec : sec3 ] , we present the numerical method . results of numerical test problems previously presented are shown in section [ sec : sec4 ] . in section [ sec : sec5 ] , we present results of numerical test problems that can not be solved accurately by previous codes .

we present a new numerical method of special relativistic resistive magnetohydrodynamics with scalar resistivity that can treat a range of phenomena , from nonrelativistic to relativistic ( shock , contact discontinuity , and alfvn wave ) . our new scheme is particularly well suited to systems with initially weak magnetic field , and mixed phenomena of relativistic and non - relativistic velocity ; for example , mri in accretion disk , and super alfvnic turbulence .

we present a new numerical method of special relativistic resistive magnetohydrodynamics with scalar resistivity that can treat a range of phenomena , from nonrelativistic to relativistic ( shock , contact discontinuity , and alfvn wave ) . the present scheme calculates the numerical flux of fluid by using an approximate riemann solver , and electromagnetic field by using the method of characteristics . since this scheme uses appropriate characteristic velocities , it is capable of accurately solving problems that can not be approximated as ideal magnetohydrodynamics and whose characteristic velocity is much lower than light velocity . the numerical results show that our scheme can solve the above problems as well as nearly ideal mhd problems . our new scheme is particularly well suited to systems with initially weak magnetic field , and mixed phenomena of relativistic and non - relativistic velocity ; for example , mri in accretion disk , and super alfvnic turbulence .

1105.5683

c

in this paper , we have presented a new numerical scheme of resistive rmhd for one - dimensional case which can solve matter dominated problems more accurately than the existing numerical method . since this new scheme uses different characteristic velocity for obtaining the numerical flux of fluid and electromagnetic field , one can solve accurately and stably problems whose characteristic velocity is much lower than that of light . when one considers relativistic problems , one has to solve stiff equations for electric fields . in general , it is difficult to deal with stiff equations , and special methods have been presented ; for example , k07 uses the strang s splitting method , and p09 use the implicit method . p09 report that strang s splitting method is incapable of solving problems that include discontinuity , such as shock . however , we find that this is not related to the method for the stiff equations , and one can solve problems including shock if one evolves the electric field during the primitive recovery ; we use strang s splitting method , and the solver is well behaved for shock tube problems . the results of other test problems show that our new scheme is capable of accurately solving both highly resistive problems and nearly ideal mhd ones . in addition , it has been shown that our code can solve low characteristic velocity problems more accurately than the hll code . the problems of high density and high plasma @xmath1 appear when one considers magnetorotational instability ( mri ) in the accretion disk with a relativistic jet , for example . in this case , one has to use relativistic resistive mhd code that can solve both highly relativistic and non - relativistic dynamics with resistivity for the following three reasons : ( 1 ) the saturation of the magnetorotational instability ( mri ) depends on the resistivity ; ( 2 ) the dynamics of an accretion disk are not ordinarily relativistic , especially , the dynamics of the mri is sub - alfvnic ; ( 3 ) the dynamics of the jet are highly relativistic . our new scheme can solve such problems accurately even when the initial magnetic field is very weak . we present multi - dimensional extension of our scheme in our next paper . we would like to thank bruno giacomazzo for providing the code computing the exact solution of the riemann problem in ideal mhd . numerical computations were in part carried out on cray xt4 at center for computational astrophysics , cfca , of national astronomical observatory of japan . this work is supported by grant - in - aids from the ministry of education , culture , sports , science , and technology ( mext ) of japan , no . 22@xmath2153369 ( t. i. ) .

since this scheme uses appropriate characteristic velocities , it is capable of accurately solving problems that can not be approximated as ideal magnetohydrodynamics and whose characteristic velocity is much lower than light velocity . the numerical results show that our scheme can solve the above problems as well as nearly ideal mhd problems .

we present a new numerical method of special relativistic resistive magnetohydrodynamics with scalar resistivity that can treat a range of phenomena , from nonrelativistic to relativistic ( shock , contact discontinuity , and alfvn wave ) . the present scheme calculates the numerical flux of fluid by using an approximate riemann solver , and electromagnetic field by using the method of characteristics . since this scheme uses appropriate characteristic velocities , it is capable of accurately solving problems that can not be approximated as ideal magnetohydrodynamics and whose characteristic velocity is much lower than light velocity . the numerical results show that our scheme can solve the above problems as well as nearly ideal mhd problems . our new scheme is particularly well suited to systems with initially weak magnetic field , and mixed phenomena of relativistic and non - relativistic velocity ; for example , mri in accretion disk , and super alfvnic turbulence .

0901.3790

r

we now test the validity of our theory by comparing our predictions against known experimental results in hot vapors , viz . in a he * cell @xcite . for he * , collisions are expected to play a favorable role through five different effects : ( i ) vccs enable one to span the entire doppler profile quickly and efficiently during optically pumping ; ( ii ) collisions aid in the feeding distortion in pumping back more atoms in @xmath13 compared to that in @xmath15 when they are entering the beam ; ( iii ) collisions increase the transit time of the atoms through the beam and hence the raman coherence lifetime @xcite ; and ( iv ) this is possible because collisions involving he atoms in the zero spin and angular momentum ground state do not depolarize the colliding he * @xcite ; and ( v ) penning ionization ( pi ) among identically polarized he * atoms is almost forbidden @xcite . we probe the general dependence of various features of interest doppler - averaged fano - like transmission profiles , the variation of the eit width , the peak transmission and the group delay with the coupling intensity on the following system characteristics : the vcc parameter @xmath142 , the unequal atomic influx parameter @xmath55 , the raman decoherence rate @xmath11 , and the initial transmission @xmath143 which carries the information about the number density of the participating atoms . in our model , the effect of collisions is incorporated through collisional dephasing of both the optical and raman coherences given in eqs.([optcoh ] ) and ( [ ramancoh ] ) , the collision - induced diffusive ( as opposed to ballistic ) transit rate @xmath33 of the atoms , a complete redistribution of the atomic population over all velocity classes leading to a velocity - independent optical pumping under rapid vcc coverage , and the vcc decoherence rate @xmath144 entering when the vcc parameter @xmath145 . for the he * system , we find that the decoherence due to vcc is very small . as @xmath142 is a deviation from the complete polarization - conservation by vcc , it should not depend on the beam size . we choose a value of @xmath146 , which helps us to obtain good fits to the measured evolutions with the coupling intensity for each of eit width , peak transmission and group delay , for all the measured beam diameters , with @xmath147 , which is simply the number of collisions per second as mentioned earlier . the excess incoming rate , @xmath148 to state @xmath13 over @xmath15 also has a distinct impact on the various features . in particular , the parameter @xmath55 = 0.1 gives satisfactory results in comparing the theoretical results with the experimentally measured evolutions . with the precisions of our measurements in he * , a constant value of @xmath55 is found to fit well for all beam diameters . the choice of the best - fit values of the parameters @xmath142 and @xmath55 for the he * system has been elaborated using the group delay plots in subsection d below . there was a slight over - estimation of the initial transmission @xmath143 for the eit experiments in he * , reported in ref.@xcite directly from the measured values , which included an effect of partial saturation by the probe power . this has been adjusted in the present paper . when the coupling beam frequency is no longer at the center of the doppler profile , transmitted intensity profiles become asymmetric . this is similar to the fano profiles obtained in the case of eit in a homogeneously - broadened medium and which have been shown to be due to interferences between a direct process and stimulated raman scattering in the overall transition probability @xcite . however , here , these profiles are modified by the fact that they have to be convoluted with the inhomogeneous doppler profile . figure [ fig2 ] shows the evolution of the transmission versus raman detuning @xmath25 for different values of the detuning @xmath149 of the coupling beam with respect to the center of the doppler profile . on the left - hand side , the measured values through a he * cell with initial transmission at resonance @xmath143 = 0.56 for a beam diameter of 1.5 cm , a coupling power of 11 mw and a probe power of 140 @xmath48w are reproduced from ref.@xcite . the base of the symmetric ( black ) curve at resonance corresponds to a transmission higher than 0.56 , because of partial saturation of the medium by the probe intensity . theoretically , the transmission profiles are generated from the imaginary part of the susceptibility at different detunings @xmath149 of the coupling beam with respect to the center of the doppler profile mentioned above . the corresponding plots on the right - hand side of fig.[fig2 ] are obtained for a beam diameter of 1.5 cm corresponding to different values of @xmath149 , with the same initial transmission , coupling and probe powers as in the experiment , using @xmath150 = 4.3 khz , @xmath151 = 0.41 khz , @xmath146 , and @xmath55 = 0.1 . the transmission profiles at all values of @xmath149 increases slightly with an increase in @xmath55 . this is also seen in the behavior of peak transmission shown in subsection c. this has been checked for a range of @xmath55 from 0 to 0.1 . there is a distinct and sensitive dependence on @xmath142 , as the tip of each profile decreases slightly with an increase of @xmath142 , and the effect is the largest on the resonant profile . as a result , there is also a change in the relative placement of the profiles . this has been checked for a range of values of @xmath142 from 10@xmath152 to 0 . the reason for this is simple . since a deviation of the value of @xmath142 from 0 indicates a loss of coherence , the transmission at resonance will be greater for @xmath142 closer to 0 , because the system is more coherent as @xmath142 approaches 0 . additionally , the effect will be more pronounced when the atomic system is in resonance with the two fields , which is the condition for a perfect eit . we thus find that the predictions from our model indeed agree very well with the experimental results . the mechanism of decoherence in eit in a room - temperature gas can be probed by measuring the width of the eit resonance as a function of the coupling beam intensity . as mentioned in the introduction , the theoretical treatment of eit in doppler - broadened gases @xcite , assuming the population exchange between the lower levels to be the main source of decoherence , predicts a _ nonlinear _ dependence for weak coupling powers : the eit width is expected to evolve with the coupling beam rabi frequency @xmath3 @xcite according to : @xmath153 where @xmath154 gives the effective width over which the atoms are pumped into the probe ground state for a fixed value of @xmath3 . in the case when @xmath155 , @xmath154 is dependent on @xmath3 and @xmath11 : @xmath156 , and the coherent population trapping is shown to be velocity selective , i.e. , it occurs only for those atoms whose frequencies are close to resonance with the coupling field . in the opposite regime , when @xmath157 , ref.@xcite predicts that @xmath158 , i.e. , in the limit of very large intensity , it is reduced to the power - broadening case . in contrast , in ref.@xcite it is assumed that all the atoms across the doppler profile are initially optically pumped by the coupling beam to the probe ground level , and the decoherence in the lower states is caused by pure dephasing , and not population exchange . then the response of the medium up to first order in probe field yields the following _ linear _ dependence of the eit linewidth on the coupling beam intensity : @xmath159 an example of the evolution of the eit width versus the intensity of the coupling beam is displayed in fig.[fig3](a ) . in the experiment with he * @xcite , the logarithm of the transmitted intensity is calculated and its full width at half maximum ( fwhm ) is then measured , in order to determine precisely the width of the susceptibility @xmath160 of the medium . the measured sub - natural ( @xmath161 ) widths for a beam diameter of 1.5 cm , a probe power of 100 @xmath48w and an initial transmission @xmath143 = 0.46 are shown as dots . theoretically , the imaginary part of the susceptibility is fitted with a lorentzian to obtain the fwhm corresponding to a particular coupling intensity . the continuous line in fig.[fig3 ] is the best fit from our model with the same parameters as in the experiment , using @xmath162 = 4.3 khz , @xmath163 = 0.41 khz , @xmath146 , and @xmath55 = 0.1 . the eit width @xmath10 is seen to evolve linearly with the coupling beam intensity , i.e. , quadratically with the coupling beam rabi frequency @xmath3 . with the experimental parameters ( @xmath164 at 1 torr , @xmath165 , @xmath166 ghz ) @xcite , one obtains @xmath167 . since the maximum rabi frequencies @xmath3 used in the experiment are smaller than @xmath168 , the measurements are in the first regime of @xcite , where @xmath169 . thus @xmath10 is predicted to evolve linearly with @xmath3 @xcite , with a slope depending on @xmath11 , but these predictions are violated in the experiment . if we use eq.([javan ] ) to fit the linear evolution of @xmath10 versus the coupling intensity , we obtain @xmath170 , which is of the same order of magnitude as @xmath171 , showing that a major part of the doppler profile takes part in the eit process . in our model we achieve the straight line feature of @xmath10 versus coupling intensity as in ref.@xcite , but without any assumptions of special initial conditions . moreover , if the data are fitted to the straight line given by eq.([lvovsky ] ) , the resulting estimate of @xmath150 does not reproduce accurately the measured evolutions of the peak - transmission and delay @xcite . our present model fits the straight line data for atomic @xmath172rb vapor at temperatures 60 - 100@xmath173c given in ref.@xcite , with appropriate values of the parameters for the optically thick system . keeping all other parameters constant , a change in the initial transmission @xmath143 , and hence in the number density of the participating atoms in the cell , does not affect the evolution of the eit width with coupling intensity in our model . likewise , a change in the unequal feeding parameter @xmath55 does not produce any visible change in the eit width . this has been checked for a range of values of @xmath174 0 to 0.5 . this is understandable as these two parameters do not affect the raman coherence lifetime but affect the pumping efficiency ( e.g. the fraction of atoms that participate in the eit phenomenon ) . figure [ fig3](b ) shows the variation of the eit width with the coupling intensity from our model for different values of the raman decoherence rate @xmath11 around the best - fit value , keeping @xmath142 , @xmath55 and @xmath143 constant . it clearly shows that the slope of the evolution is the same for different values of @xmath11 . note that different laser beam diameters would lead to different transit times of the atoms through the beam , and hence different @xmath33 . the motion of the atoms through the beam is assumed to be diffusive , as stated previously , because of the large number of collisions they undergo . the raman decoherence rate @xmath11 given by eq.(15 ) thus contains a variable @xmath33 plus other terms . for the he * measurements , we estimate that @xmath175 4 khz for a low pressure of 1 torr and an ambient magnetic field inhomogeneity . this is obtained by estimating first @xmath33 for a particular beam diameter , and then @xmath11 from the best fit of ( primarily ) the eit - width data . in the experiment , the beam diameters are generally not precisely known , because the beam emerging from the acousto - optic modulators is not perfectly gaussian . this affects the precise determination of the transit times as well as beam intensities ( the probe and coupling powers measured before the he * cell were , of course , their average values ) and rabi frequencies . we have , however , checked that the experimental data for different beam sizes yield the @xmath33 values following the diffusive transit scenario . figure [ fig3](c ) shows the variation for different values of the vcc parameter @xmath142 . the slope of the evolution is the same for different values of @xmath120 but the intercept increases with an decrease of @xmath142 . from figs.[fig4](b ) and ( c ) , the width - intercept at @xmath3 = 0 are seen to depend on the parameters @xmath11 and @xmath142 , yielding a narrower resonance for a lower @xmath11 or a lower @xmath142 . the inset shows that the measured data fit better with @xmath145 and @xmath176 . however , the lines do not fit eq.([lvovsky ] ) , with @xmath11 of ref.@xcite simply replaced here by @xmath177 . as pointed out earlier , in the density - matrix equations , the vcc contribution gets added to the transit time decay ( and hence the raman coherence relaxation ) rate as @xmath178 , except in the inhomogeneous term signifying atomic influx in the populations in the lower levels at the transit rate @xmath33 which has no contribution from the vcc . it is therefore not surprising that the net effect of @xmath142 can not be taken care of by @xmath33 or @xmath11 . figure [ fig3](d ) shows the variation of the eit width with the coupling intensity from our model for different values of the optical coherence decay rate @xmath73 . the slope of the line changes inversely with changes in the values of @xmath4 and @xmath73 . we next consider the maximum probe transmission at resonance ( @xmath149 = 0 ) corresponding to different coupling intensities . figure [ fig4](a ) shows the evolution of the cell transmission versus coupling beam intensity . the measured values ( dots ) through a he * cell for a beam diameter of 1.5 cm are reproduced from ref.@xcite . the corresponding continuous curve is obtained from our theory by calculating the transmission at two - photon resonance @xmath179 , with @xmath146 , @xmath55 = 0.1 at the same initial transmission and probe power as in the experiment : probe power of 70 @xmath48w , @xmath143 = 0.46 , @xmath150 = 4.3 khz , and @xmath163 = 0.41 khz . using the same hypotheses as for the derivation of eq.([lvovsky ] ) @xcite , the peak transmission is predicted to evolve as @xcite : @xmath180 it is seen that there is a better agreement of the experimental result with our present theory than what was obtained using eq.([lvovsky_trans ] ) in ref.@xcite with the value of @xmath11 deduced from the eit - width data , in spite of the fact that we do not assume @xmath181 = 1 , i.e. , a system perfectly prepared by optical pumping at @xmath47 = 0 as in ref.@xcite , is redundant here in the presence of rapid vcc coverage . figure [ fig4](a ) also shows the variation of the peak transmission with the coupling intensity from our model for different values of the vcc parameter @xmath142 . the dotted and the dashed plots correspond to @xmath142 = 0 and @xmath182 , respectively . it can be thus inferred that the peak transmission increases with a decrease in @xmath142 . this also has support from the effect of @xmath142 on the doppler - broadened profiles in fig.[fig2 ] for the same reason . the best - looking fit for @xmath146 emphasizes that the depolarization due to vccs is a small effect , as expected from the work of shlyapnikov _ et al . _ @xcite . figure [ fig4](b ) shows the variation of the peak transmission with the coupling intensity from our model for different values of the raman decoherence rate @xmath11 around the best - fit value , when @xmath142 , @xmath55 and @xmath143 are kept constant @xcite . it is clear that a lower decoherence rate @xmath11 leads to a more coherent system , and thus @xmath150 = 3.2 khz ( dashed curve ) yields the highest peak transmission compared to the rest shown in this plot . thus the evolutions from our model are consistent with our physical understanding . also note that figs.[fig4](a ) and ( b ) show that an increase in @xmath11 has a similar effect as a decrease in @xmath142 . figure [ fig4](c ) shows the same for different values of the unequal feeding parameter @xmath55 from the theory . the effect of @xmath55 here is clearly very distinct . as @xmath55 increases , there are more atoms entering the laser beam in the dark state @xmath13 . thus , the peak transmission at two - photon resonance will also increase as the transparency is more when more atoms can participate in the eit phenomenon . figure [ fig4](d ) shows the effect of different values of the initial transmission @xmath143 . it is obvious that a higher initial transmission @xmath143 would lead to a higher peak transmission for non - zero coupling intensities . figure [ fig5](a ) shows the measured evolution of the group delay ( through a he * cell of length 2.5 cm ) versus coupling beam intensity for a beam diameter of 1.5 cm ( dots ) , reproduced from ref.@xcite . the results have been obtained with gaussian probe pulses of duration of 70 @xmath48s with a peak power of 35 @xmath48w and with the coupling and probe beam frequencies at the center of the doppler profile ( @xmath183 ) . in the slow - light experiments performed with he * , reported in ref.@xcite , the measured delays for non - zero coupling intensities were slightly overestimated as the reference used was the probe pulse in the absence of a coupling beam . theoretically , the group delay is calculated from the derivative of the real part of the susceptibility with respect to frequency at two - photon resonance , for the experimentally used parameters . the continuous curve in fig.[fig5](a ) is the best fit obtained from our model with @xmath150 = 4.3 khz , @xmath163 = 0.41 khz , @xmath146 and @xmath55 = 0.1 , for the same probe power of 35 @xmath48w and the same initial transmission @xmath143 = 0.46 as in the experiment . the group velocity derived @xcite from the susceptibility of ref.@xcite leads to a group delay at the line center ( @xmath183 ) given by : @xmath184 ^ 2}\;. \label{lvovsky_delay}\ ] ] the maximum value of the group delay is reached for @xmath185 and its value is @xmath186 . again , there is a better agreement of the experimental results with our present theory than what was obtained in ref.@xcite using eq.([lvovsky_delay ] ) , with the value of @xmath11 deduced from the eit - width data . figure [ fig5](a ) also shows the comparison of the group delay profiles from our theory for different values of @xmath187 ( dashed curve ) and 0 ( dotted curve ) around the best - fit value corresponding to @xmath146 ( continuous curve ) , for the 1.5 cm - diameter beam . the magnified part shown in the inset justifies the choice of the vcc parameter value of @xmath146 for the measured data for he * , which is distinct from that of @xmath125 . as mentioned earlier , the measured data were over - estimated and a good fit running slightly below the data points would require a sensitive adjustment of @xmath188 ( as shown ) . figure [ fig5](b ) shows the comparison of the group delay profiles from the theory for different values of @xmath11 around the best - fit value , for the 1.5 cm - diameter beam . @xmath11 indeed has a great impact on the delay which is clear because lower the value of @xmath11 ( for example , the dashed curve for @xmath150 = 3.2 khz ) , more is the coherence , hence higher are the delays achieved in the system . figure [ fig5](c ) shows the same as above for different values of @xmath55 around the best - fit value , for a range of @xmath55 from 0 to 0.5 . we see that with an increase of @xmath55 , the delays at different coupling intensities decrease . on comparison with the plots of peak transmission for different values of @xmath55 in fig.[fig4](c ) , one deduces that the effect of @xmath55 on these two characteristics are opposite . we can understand this as follows . if an increase of @xmath55 increases the peak transmission ( as seen and explained above ) , then from the relationship of resonant peak transmission and delay , it becomes clear that an increased transmission would lead to a decrease in the group delay . this is also manifested in eqs.([lvovsky_trans ] ) and ( [ lvovsky_delay ] ) . the inset at a magnified scale shows the comparison of the plots for @xmath189 and @xmath190 with reference to the measured data points it is clear that @xmath190 provides a distinctly better fit than @xmath189 . figure [ fig5](d ) shows the comparison of the group delay profiles from the theory for different values of @xmath143 around the best - fit value , for the 1.5 cm - diameter beam . the group delay increases with a decrease in @xmath143 and the effect is also supported by eq.([lvovsky_delay ] ) . a decrease in the initial transmission in the absence of the coupling field signifies a proportionate increase in the number of participating atoms . @xmath143 , however , does not affect the eit width . thus the delay - bandwidth product , which is a figure of merit for a delay / storage medium , turns out to be proportional to the number density of the medium . in comparison to the width and the peak transmission plots shown in figs.[fig3 ] and [ fig4 ] respectively , we note that @xmath11 , @xmath142 , @xmath55 and @xmath143 have a greater impact on the delay as seen from fig.[fig5 ] , especially in determining the peak of the delay curve .

velocity - changing collisions ( vccs ) are modeled in the strong collision limit effectively , which helps in achieving optical pumping by the coupling beam across the entire doppler profile . the predictions , taking into account a dynamic rate of influx of atoms in the two lower levels of the , are in excellent agreement with the reported experimental results forhe*. the role played by the vcc parameter is seen to be distinct from that by the transit time or raman coherence decay rate .

we present a realistic theoretical treatment of a three - level system in a hot atomic vapor interacting with a coupling and a probe field of arbitrary strengths , leading to electromagnetically - induced transparency and slow light under the two - photon resonance condition . we take into account all the relevant decoherence processes including collisions . velocity - changing collisions ( vccs ) are modeled in the strong collision limit effectively , which helps in achieving optical pumping by the coupling beam across the entire doppler profile . the steady - state expressions for the atomic density - matrix elements are numerically evaluated to yield the experimentally measured response characteristics . the predictions , taking into account a dynamic rate of influx of atoms in the two lower levels of the , are in excellent agreement with the reported experimental results forhe*. the role played by the vcc parameter is seen to be distinct from that by the transit time or raman coherence decay rate .

0901.3790

c

we have presented a realistic analysis of eit and slow light in a hot atomic vapor , taking into account all the relevant decoherence processes , for arbitrary strengths of the probe and the coupling fields , and without assuming any special initial condition . we have considered the influx of fresh atoms in the lower levels and the outflux from all the levels at a transit rate in the gas . unlike the theory for eit in a doppler - broadened medium in ref.@xcite in which the role of collisions is completely neglected , our analysis includes phase - interrupting collisions of active atoms as well as velocity - changing collisions , modeled effectively in the strong collision limit . we have demonstrated the role of vccs in redistributing the atomic population over all velocity classes and hence a velocity - independent optical pumping . the initial condition of @xmath191 = 1 , i.e. , a system perfectly prepared by optical pumping at @xmath47 = 0 in ref.@xcite , is redundant here in the presence of rapid vcc coverage . the steady - state solutions for the atomic density matrix elements are presented in the strong - collision approximation with a model for the vccs under rapid vcc coverage . a value of the vcc parameter @xmath192 indicates a loss of coherence by vccs . as observed from the results , all the eit characteristics have a sensitive dependence on @xmath142 . in our example of the he * system @xcite , it was found that a small value of @xmath146 gives the best fits for all the measured characteristics for different beam sizes . for he * , the motion of the atoms through the beam is assumed to be diffusive , because of the large number of collisions they undergo . further , because of diffusion and favourable collisions outside the interaction region , we have allowed a slightly greater fraction of atoms to enter the beam prepared in state @xmath13 than those in state @xmath15 using a parameter @xmath55 . the best fit value of @xmath193 supports this fact . for all systems in which other decoherence effects are small so that atoms can diffuse out of the interaction region and return before decohering , the unequal feedback fraction would model such a positive contribution to the coherence , similar in effect to a decrease in the number density or an increase in the initial transmission @xmath143 . a constant value of @xmath55 is found to fit different beam sizes , given the precision of the reported measurements . for non - zero detunings @xmath149 of the coupling field from the center of the doppler - broadened transition frequency , the transmitted intensity profiles become asymmetric about the two - photon resonance ( raman detuning @xmath25 = 0 ) . this fano - like feature is a signature of the two - photon process of eit , and emerges naturally from our model . the eit width @xmath10 , simulated from our model , shows a linear dependence on the coupling beam intensity , i.e. , a quadratic dependence on the coupling beam rabi frequency @xmath3 , as observed in experiments . the evolutions of the peak transmission and the group delay with the coupling beam intensity predicted from our analysis faithfully reproduce the experimentally observed behaviors . in the evolution of all these features of interest , an increase in the raman decoherence rate @xmath11 seems in general to have a similar effect as an increase in the vcc parameter @xmath142 . but whatever the beam diameter , @xmath142 should remain constant , while @xmath33 and hence @xmath11 should decrease when the beam diameter increases ( keeping @xmath194 constant ) . eit has recently found applications in white - light cavities @xcite for use in gravitational wave detection . for applications of slowing of light for use in quantum - information processing , and in particular , in quantum memory , the medium needs to be optically dense . our model is applicable to all such systems of hot atomic vapor , which are attractive candidates for practical applications requiring large - bandwidth controllable delays , for example , for signal processing at the appropriate wavelength . the system can be generalized to model tripod - like systems @xcite in hot vapor . this work is supported by an indo - french networking project funded by the department of science and technology , government of india , and the french ministry of foreign affairs . the work was initiated during a stay of rg in france , supported also by `` cnano ile - de - france '' and `` triangle de la physique '' . the authors wish to thank e. arimondo , h. gilles , d. kumar , m. leduc , p. j. nacher and g. tastevin for useful discussions . the work of jg is supported by the council of scientific and industrial research , india . the school of physical sciences , jawaharlal nehru university , is supported by the university grants commission , india , under a departmental research support scheme . s. knappe , r. wynands , j. kitching , h. g. robinson and l. hollberg , j. opt . b * 18 * , 1545 ( 2001 ) ; j. vanier , a. godone , and f. levi , phys . a * 58 * , 2345 ( 1998 ) ; m. erhard and h. helm , phys . a * 63 * , 043813 ( 2001 ) ; i. novikova , d. f. phillips , a. s. zibrov , r. l. walsworth , a. v. taichenachev and v. i. yudin , opt . lett . * 31 * , 2353 ( 2006 ) . in both refs.@xcite and @xcite , in order to avoid the complexity in the integration with a maxwell - boltzmann velocity distribution , the usual gaussian distribution has been approximated with a lorentzian function , leading to small deviations . the interesting effect of diffusion - induced ramsey narrowing " has the same origin ; see , for example , y. xiao , i. novikova , d. f. phillips and r. l. walsworth , phys . * 96 * , 043601 ( 2006 ) . it occurs due to the random distribution of the durations spent by the atom outside the interaction region . instead of treating the atomic motion in a separate diffusion equation , the effect here has been easily incorporated in the parameter @xmath55 . e. arimondo , phys . a * 54 * , 2216 ( 1996 ) . note that in this paper the collisional relaxation rate and kernel for populations in eq.(15b ) should have the superscript @xmath195 , and not @xmath196 . in deriving eqs.(16 ) , it has been assumed that @xmath197 = 0 , and @xmath198 in the cpt system . also , the maxwell distribution @xmath96 in eq.(18 ) has a mistake : the @xmath101 in the denominator should be deleted . the distribution @xmath96 is then the usual normalized maxwell distribution with the dimensions of inverse speed . the dimensionality of eq.(17 ) is now balanced . @xmath199s in eq.(11 ) are dimensionless . then @xmath200 introduced in eq.(21 ) has the dimensions of speed . but the @xmath200s given in the solution ( 25 ) are dimensionless . in deriving the dynamical eqs.(16 ) and ( 22 ) , the steady - state values of the optical coherences have been used . a. v. phelps , phys . rev . * 99 * , 1307 ( 1955 ) ; m. g. payne _ et al_. , phys lett . * 35 * , 1154 ( 1975 ) ; m. pinard and f. lalo , j. phys . france * 41 * , 799 ( 1980 ) ; b. zygelman , phys . a * 43 * , 575 ( 1991 ) . other than the anomaly related to the actual beam size inside the cell as mentioned in the text , note that the three sets of data for the eit width and the two sets of data for peak transmission in ref.@xcite were generated under different experimental conditions , notably the initial transmission @xmath143 , signifying differences in the number density of the participating atoms in the he * discharge cell . likewise , the transit time of the atoms in the beam , influenced by collisions , and the collisional dephasing @xmath201 , would be different for these different measurements . the best fits from our theory are consistent with the logical adjustments of both @xmath143 and @xmath11 for these different sets of data . note that in the calculation of the control field rabi frequency @xmath3 in ref.@xcite , the oscillator strength for the transition has been erroneously taken as the total @xmath202 instead of @xmath203 ( in case of degenerate zeeman sublevels , when a circularly - polarized light probes the transition along any one arm of the @xmath0-system , the oscillator strength is half of the total @xmath204 . ) . it has resulted in a scaling of @xmath3 , which has been corrected here . this has no bearing on the conclusions drawn in ref.@xcite .

we present a realistic theoretical treatment of a three - level system in a hot atomic vapor interacting with a coupling and a probe field of arbitrary strengths , leading to electromagnetically - induced transparency and slow light under the two - photon resonance condition . the steady - state expressions for the atomic density - matrix elements are numerically evaluated to yield the experimentally measured response characteristics .

we present a realistic theoretical treatment of a three - level system in a hot atomic vapor interacting with a coupling and a probe field of arbitrary strengths , leading to electromagnetically - induced transparency and slow light under the two - photon resonance condition . we take into account all the relevant decoherence processes including collisions . velocity - changing collisions ( vccs ) are modeled in the strong collision limit effectively , which helps in achieving optical pumping by the coupling beam across the entire doppler profile . the steady - state expressions for the atomic density - matrix elements are numerically evaluated to yield the experimentally measured response characteristics . the predictions , taking into account a dynamic rate of influx of atoms in the two lower levels of the , are in excellent agreement with the reported experimental results forhe*. the role played by the vcc parameter is seen to be distinct from that by the transit time or raman coherence decay rate .

1306.6073

i

the importance of chiral symmetry in hadron physics has been understood for more than 50 years . as an explicit lagrangian representation of the approximate chiral symmetry ( pcac ) that had been recognized in low energy pion nucleon interactions , gell - mann and levy @xcite constructed the extremely successful linear sigma model . in that model the pion couples to the nucleon through pseudoscalar coupling , while an additional scalar ( @xmath1 ) field is also coupled linearly . at a more formal level , gell - mann @xcite proposed su(2)@xmath2su(2 ) as an exact algebra for the charges associated with the hamiltonian governing the strong interaction , even though chiral symmetry was not an exact symmetry of that hamiltonian . on the basis of current algebra one can show very generally that the amplitude for pion scattering or production must vanish as the four - momentum of the pion vanishes @xcite . within the linear sigma model , this important result for low energy pion - nucleon scattering , for example , is only possible through a subtle cancellation of two large contributions , the first involving pion emission and absorption through the pseudoscalar ( ps ) coupling , and the second involving @xmath1 exchange in the @xmath3-channel . keeping track of the necessary cancellations between such large terms in the linear sigma model is tedious and for that reason modern formulations of chiral effective field theory tend to prefer a lagrangian formulation based on a nonlinear realization of chiral symmetry @xcite . in such a formulation the natural @xmath4 vertex involves pseudovector ( pv ) coupling and the vanishing of pion nucleon scattering amplitudes as the pion four - momentum vanishes emerges trivially . in this work , motivated by the phenomenological simplicity of enforcing soft - pion theorems , we focus on the case of pv coupling . however , since the linear realization of chiral symmetry is still used in the literature , for completeness we also compare our results with those for ps coupling . more recently , chiral symmetry and the pion cloud of the nucleon have been shown to play a central role in understanding various flavor and spin asymmetries in quark distribution functions measured at high energies . most prominent of these has been the su(2 ) flavor asymmetry in the proton sea , with the large excess of @xmath5 quarks over @xmath6 being predicted in ref . @xcite and found in deep - inelastic scattering @xcite and drell - yan experiments @xcite . while a nonperturbative pionic component of the nucleon wave function provides a natural explanation for the sign of the observed asymmetry , calculations of the magnitude of the @xmath7 difference have typically been made in models without a direct connection to qcd . furthermore , while the most convenient framework for describing high - energy reactions is the light - front , the realization of chiral symmetry on the light - front is yet to be fully understood ( for a recent discussion see , _ e.g. _ , ref . @xcite ) . in ref . @xcite we examined the framework dependence of pion loop effects for the simple case of the nucleon self - energy . we showed that results for the model - independent , nonanalytical behavior associated with the long - range part of the pion cloud @xcite are in fact independent of whether the calculation is performed using light - front , instant form ( in the rest frame or infinite momentum frame ) , or covariant perturbation theory . on the other hand , important differences were observed for the nonanalytic structure of the self - energy when comparing the pv and ps couplings . applying the methodologies developed in refs . @xcite , we consider here the more physically relevant case of the electromagnetic coupling of the nucleon dressed by pion loops . this represents the necessary next step towards the computation of the chiral corrections to quark distribution functions of the nucleon , whose moments are given by matrix elements of twist-2 operators . the twist-2 matrix elements were studied previously by chen and ji @xcite and arndt and savage @xcite , who computed the most important pion loop contributions to the leading nonanalytic behavior within heavy baryon chiral perturbation theory . in the present analysis we compute the pion loop corrections to the vertex renormalization factors using a fully relativistic framework , which includes higher order corrections in the pion mass @xmath0 . furthermore , we demonstrate explicitly that gauge invariance and the ward - takahashi identities hold to all orders @xmath0 , provided the full set of one - loop diagrams is considered , including rainbow , tadpole and kroll - ruderman contact terms . we verify this for both pv and ps theories . using the results for the vertex corrections , we then derive the pion loop corrections to the matrix elements of the twist-2 operators for both the proton and neutron , and verify the nonanalytic behavior of the isoscalar and isovector contributions . note that for the lowest moment of the nonsinglet distribution the chiral corrections are essentially those that appear for the nucleon electromagnetic form factors at zero four - momentum transfer squared , @xmath8 . these have been computed in a relativistic formalism to one loop order in refs . in contrast to form factors , for high - energy observables such as quark distribution functions the natural framework is the light - front , to which we specialize in this work . while we also focus on the lowest moment of the quark distributions , for the reconstruction of the distributions themselves @xcite , higher moments of the distributions will of course be necessary ( sec . [ sec : me ] ) . in sec . [ sec : pin ] we review the basics of the pion nucleon interaction in terms of the chiral lagrangian evaluated to lowest order in derivatives of the pion field . the electromagnetic nucleon vertex corrections arising from pion loops are computed in sec . [ sec : z1 ] , and their nonanalytic properties studied as a function of the pion mass . to illustrate the role of the various contributions to the vertex renormalization explicitly , we compute the renormalization factors numerically as a function of the ultraviolet cutoff . the results for the vertex corrections and wave function renormalization are subsequently used in sec . [ sec : me ] to compute the chiral corrections to nucleon matrix elements of twist-2 operators . comparison of the results for pv and ps coupling also allows us to identify the origin of the discrepancy between the nonanalytic behaviors of the twist-2 moments computed in heavy baryon chiral perturbation theory and at the parton level in terms of the sullivan process @xcite . finally , in sec . [ sec : conc ] we summarize our findings and outline future extensions of the present work . in appendix [ app : feyn ] we collect formulas for the complete set of feynman rules needed to compute the vertex renormalization and wave function corrections . the demonstration that the results respect gauge invariance and the ward - takahashi identity is presented in appendices [ app : gi ] and [ app : wti ] , respectively , and some useful results for the nonanalytic behavior of integrals are listed in appendix [ app : lna ] . although some of the formal results which we summarize here can be found elsewhere , our aim will be to provide a pedagogical discussion of the derivations in order to clarify some conflicting claims in the literature about the computation of the analytic and nonanalytic contributions to the pion loop integrals .

vertex and wave function renormalization constants are computed to lowest order in the pion field , including their nonanalytic behavior in the chiral limit , and studied numerically as a function of the ultraviolet cutoff . particular care is taken to explicitly verify gauge invariance and ward - takahashi identity constraints to all orders in the expansion .

we present a relativistic formulation of pion loop corrections to the coupling of photons with nucleons on the light - front . vertex and wave function renormalization constants are computed to lowest order in the pion field , including their nonanalytic behavior in the chiral limit , and studied numerically as a function of the ultraviolet cutoff . particular care is taken to explicitly verify gauge invariance and ward - takahashi identity constraints to all orders in the expansion . the results are used to compute the chiral corrections to matrix elements of local operators , related to moments of deep - inelastic structure functions . finally , comparison of results for pseudovector and pseudoscalar coupling allows the resolution of a long - standing puzzle in the computation of pion cloud corrections to structure function moments .

1306.6073

c

in this work we have presented a detailed analysis of pion cloud corrections to the electromagnetic coupling of the nucleon , using the lowest order effective lagrangian constrained by the chiral symmetry of qcd . we have computed the complete set of vertex corrections arising from the various one - loop diagrams , including rainbow diagrams with pion and nucleon coupling , kroll - ruderman contributions , and tadpole and bubble diagrams associated with @xmath58 contact interactions . explicit evaluation of the vertex renormalization factors allowed us to directly verify relations between the nucleon and pion coupling diagrams , and demonstrate the consistency of the theory with electromagnetic gauge invariance . the kr terms in particular are essential for ensuring gauge invariance to all orders in the pion mass , even though these do not contribute to the leading nonanalytic behavior of the vertex factors . we have also shown that the sum of the pion tadpole and bubble diagrams vanishes . we have examined the chiral expansion of all the vertex corrections as a function of the pion mass @xmath0 , computing the coefficients of the nonanalytic terms up to and including order @xmath195 . the lna terms agree with earlier calculations in heavy baryon chiral perturbation theory @xcite , although our formulation is relativistic and allows for higher order corrections in @xmath196 . comparison of the results for the pseudoscalar @xmath58 theory reveals the origin of the long - standing discrepancy between the lna behavior in the chiral effective theory and in approaches based on the sullivan process @xcite which use a @xmath197 coupling . to study the behavior of the total vertex corrections , rather than just their longest - range lna contributions , we have computed the vertex renormalization factors numerically as a function of the transverse momentum cutoff used to regularize the integrals . the pion and nucleon rainbow corrections give positive contributions to the vertex renormalization factor @xmath198 for the range of cutoffs considered here ( @xmath199 gev ) , while the contribution from the kr diagram is negative . the overall magnitude of the vertex correction is @xmath200 for @xmath201 gev and @xmath202 for @xmath203 gev . the tadpole and bubble contributions range up to @xmath204 for @xmath203 gev . although a transverse momentum cutoff breaks the lorentz invariance of the @xmath58 theory , for the purposes of the present study it is sufficient to illustrate the relative contributions of the various pion loop diagrams . for a more quantitative analysis , for example , of the corrections to the @xmath7 pdf difference , a covariant regularization scheme can be used @xcite . finally , using the results for the vertex and wave function renormalization constants we computed the pion loop corrections to the matrix elements of twist-2 operators for the proton and neutron , which in the operator product expansion are related to moments of parton distribution functions . for the lowest moment , we demonstrated explicitly that the pion loop corrections cancel for the isoscalar combination of moments for the nucleon and pion couplings separately . the isovector moments , on the other hand , were found to have the characteristic @xmath51 leading dependence for both the nucleon and pion coupling diagrams ( with the sum of course canceling , as required by charge conservation ) . again , comparison of the pv and ps results for the moments enabled us to clearly identify the source of the difference between the coefficients of the lna terms in the two theories . while the pv theory is clearly preferred by considerations of chiral symmetry , the explicit demonstration that the ps theory can be made consistent in this context with the introduction of a scalar @xmath1 field remains an interesting challenge . the results derived here can be used in the future to investigate the nonanalytic behavior of the nucleon pdfs , particularly the extrapolation of calculations in lattice qcd performed at unphysically large quark masses @xcite to the physical region . our findings will also pave the way for phenomenological studies , especially the quest for a consistent interpretation of the physics of the pion cloud at the parton level , enabling deeper studies of the origin of the @xmath7 asymmetry @xcite . in addition , this work will also guide investigation of the very important asymmetry between the @xmath205 and @xmath206 distributions , with its connection to the five - quark component of the nucleon wave function , as well as the spin - flavor asymmetry @xmath207 between the polarized @xmath6 and @xmath5 distributions .

we present a relativistic formulation of pion loop corrections to the coupling of photons with nucleons on the light - front . the results are used to compute the chiral corrections to matrix elements of local operators , related to moments of deep - inelastic structure functions . finally , comparison of results for pseudovector and pseudoscalar coupling allows the resolution of a long - standing puzzle in the computation of pion cloud corrections to structure function moments .

we present a relativistic formulation of pion loop corrections to the coupling of photons with nucleons on the light - front . vertex and wave function renormalization constants are computed to lowest order in the pion field , including their nonanalytic behavior in the chiral limit , and studied numerically as a function of the ultraviolet cutoff . particular care is taken to explicitly verify gauge invariance and ward - takahashi identity constraints to all orders in the expansion . the results are used to compute the chiral corrections to matrix elements of local operators , related to moments of deep - inelastic structure functions . finally , comparison of results for pseudovector and pseudoscalar coupling allows the resolution of a long - standing puzzle in the computation of pion cloud corrections to structure function moments .

astro-ph9810374

i

the discovery that the sky distribution of faint gamma - ray bursts ( grbs ) is isotropic , coupled with the confirmation of a roll - over in the cumulative brightness distribution of the bursts , suggested that the bursts lie at cosmological distances ( @xcite ) . about one year ago , the rapid dissemination of arcminute - sized grb error circles provided by the wide - field camera ( wfc ) on bepposax ( @xcite ) led to the discovery of fading x - ray ( @xcite ) and optical ( @xcite ) counterparts to the bursts . the subsequent measurement of absorption lines at @xmath5 in the spectra of the optical afterglow of grb 970508 ( @xcite ) firmly established the extra - galactic nature of this burst , and presumably , of most or all grbs . redshifts are now known for the apparent host galaxies of two other bursts : @xmath6 in the case of grb 980703 ( @xcite ) and @xmath7 in the case of grb 971214 ( @xcite ) . grb980425 has complicated this simple `` cosmological '' picture of grbs . following the detection of this burst by the bepposax gamma - ray burst monitor and wfc ( @xcite ; see also @xcite ) , x - ray follow - up observations were made using the bepposax narrow field instrument ( nfi ) ( pian et al . 1998a , b ; piro et al . the initial observation revealed a faint x - ray source ( detected at the @xmath8 level ) that was not seen in several subsequent observations . optical follow - up observations led to the discovery of a supernova , sn 1998bw , within the 8 arcminute radius of the beppposax wfc error circle for the grb but not coincident with the fading x - ray source ( @xcite ) . no other optically variable object was detected within the bepposax wfc error circle for the burst . sn 1998bw was subsequently found to be of type ic ( @xcite ) and very bright in the radio ( @xcite ) . the supernova is coincident with a galaxy ( presumably the host galaxy ) that lies at @xmath9 ( @xcite ) . an association between grb 980425 and sn 1998bw is an intriguing possibility , made more so by the recent heightened interest in `` collapsar '' or `` hypernova '' models of grbs ( woosley 1993 ; woosley , eastman & schmidt 1998 ; @xcite ; @xcite ) . the principal argument in favor of an association between grb 980425 and sn 1998bw is the positional and temporal coincidence between the two events . given a supernova rate of @xmath10 per @xmath11 galaxy per century ( @xcite ) , a density of @xmath11 galaxies of 0.01 mpc@xmath12 , and that approximately 2/7 of these are sne of types ib , ib / c and ic ( @xcite , @xcite ) , the chance probability of such a spatial - temporal coincidence for a type ib - ic sn with @xmath13 is @xmath14 . but would an association between grb980425 and sn 1998bw be acceptable sn 1998bw were at @xmath15 rather than at @xmath16 ? almost certainly . if so , the appropriate value for the chance probability of the positional and temporal coincidence becomes @xmath17% . this illustrates how difficult it is to evaluate _ a posteriori _ statistical arguments . and there are specific reasons to be cautious in this case . assuming a power - law decay with time , and connecting the 2 - 10 kev x - ray flux detected by the bepposax wfc during and immediately following the burst , and the 2 - 10 kev x - ray flux of the fading x - ray source detected 10 hours later by the bepposax nfi , yields a power - law index of @xmath18 ( @xcite ) , which is similar to the power - law indices of the x - ray afterglows of other bepposax bursts . thus grb 980425 is more plausibly associated with this fading x - ray source than with sn 1998bw . also , if the association between grb 980425 and sn 1998bw were true , the luminosity of this burst would be @xmath19 erg s@xmath20 and its energy would be @xmath21 erg . each would therefore be five orders of magnitude less than that of other bursts , and the behavior of the x - ray and optical afterglow would be very different from those of the other bepposax bursts , yet the burst itself is indistinguishable from other bepposax and batse grbs with respect to duration , time history , spectral shape , peak flux , and and fluence ( @xcite ) . in view of the difficulty in assessing the significance of any association between sne and grbs on the basis of this single event , the safest procedure is to regard the association as a hypothesis that is to be tested by searching for correlations between sne and grb in catalogs of sne and grbs , excluding sn 1998bw and grb980425 . wang & wheeler ( 1998 ) have performed such a study , and find evidence for a significant ( at the @xmath22 level ) correlation between type ib - ic sne and grbs detected by batse . while the results of wang & wheeler ( 1998 ) seem promising , their study suffers from several deficiencies . the number ( six ) of type ib - ic sne in their sample is small , and one of these events is mis - classified [ sn 1992ad is a type ii sn ( @xcite ) , not a type ic sn ] , which eliminates one of their sn - grb associations . the range of possible explosion dates that we derive for another event ( sn 1997x ) is much smaller than the range they allow , which rules out another of their associations . furthermore , two other sn grb associations are ruled out by interplanetary network positions ( @xcite ) . moreover , wang & wheeler s methodology is somewhat arbitrary , in the sense that they increase the size of the batse grb positional error circles by a large , arbitrary factor . finally , wang & wheeler s methodology makes no provision for the fact that the batse temporal exposure is less than unity . in fact , their result ( six of six `` type ib - ic '' sne correlated with grbs ) is unlikely , even if the proposed association between type ib - ic sne and grbs were real , since batse has on average a probability of 0.48 of detecting any given grb because of earth blocking and other effects ( @xcite ) . here we carry out an analysis that overcomes these deficiencies . we correct the `` type ib - ic '' sn sample of wang & wheeler ( 1998 ) and supplement it with 15 additional type ib - ic sne , so that we can study a larger sample . further , we develop an alternative method , based on bayesian inference and therefore using the likelihood function , that incorporates information about the batse position errors in a non - arbitrary way and that is free of the ambiguities of _ a posteriori _ statistics . the method also accounts the fact that the batse temporal exposure is less than unity . applying this method to a sample of 83 type ia sne and a sample of 20 type ib - ic sne , we find overwhelming odds against the hypothesis that all type ia sne produce observable gamma - ray bursts , irrespective of whether the sne are at low- or high - redshift , and very large odds against the hypothesis that all type ib , ib / c , and ic sne produce observable gamma - ray bursts . we find large odds against the hypothesis that a fraction of type ia supernovae produce observable gamma - ray bursts , and moderate odds against the hypothesis that a fraction of type ib , ib / c , and ic supernovae produce observable bursts . we have also re - analyzed both a corrected version of the wang & wheeler sample of type ib - ic sne and our larger sample of 20 type ib - ic sne , using a generalization of their frequentist method . we find no significant evidence in either case of a correlation between type ib - ic sne and grbs , consistent with the very strong evidence against such a correlation that we find from our bayesian analysis . the plan of this paper is as follows . in ii we present a rigorous method , based on bayesian inference , for calculating the odds favoring the hypothesis that any particular class of astronomical transients produces grbs over the hypothesis that they do not . in iii we apply this method to various subclasses of type i sne . in iv we discuss our results , and compare them with other work . we present our conclusions in v.

we present a rigorous method , based on bayesian inference , for calculating the odds favoring the hypothesis that any particular class of astronomical transients produce gamma - ray bursts over the hypothesis that they do not . we then apply this method to a sample of 83 type ia supernovae and a sample of 20 type ib - ic supernovae . we find overwhelming odds against the hypothesis that all type ia supernovae produce gamma - ray bursts , whether at low redshift ( ) or high - redshift ( ) , and very large odds ( ) against the hypothesis that all type ib , ib / c , and ic supernovae produce observable gamma - ray bursts . we find large odds ( ) against the hypothesis that a fraction of type ia supernovae produce observable gamma - ray bursts , and moderate odds ( ) against the hypothesis that a fraction of type ib - ic supernovae produce observable bursts . we have also re - analyzed both a corrected version of the wang & wheeler sample of type ib - ic sne and our larger sample of 20 type ib - ic sne , using a generalization of their frequentist method . we find no significant evidence in either case of a correlation between type ib - ic sne and grbs , consistent with the very strong evidence against such a correlation that we find from our bayesian analysis .

we present a rigorous method , based on bayesian inference , for calculating the odds favoring the hypothesis that any particular class of astronomical transients produce gamma - ray bursts over the hypothesis that they do not . we then apply this method to a sample of 83 type ia supernovae and a sample of 20 type ib - ic supernovae . we find overwhelming odds against the hypothesis that all type ia supernovae produce gamma - ray bursts , whether at low redshift ( ) or high - redshift ( ) , and very large odds ( ) against the hypothesis that all type ib , ib / c , and ic supernovae produce observable gamma - ray bursts . we find large odds ( ) against the hypothesis that a fraction of type ia supernovae produce observable gamma - ray bursts , and moderate odds ( ) against the hypothesis that a fraction of type ib - ic supernovae produce observable bursts . we have also re - analyzed both a corrected version of the wang & wheeler sample of type ib - ic sne and our larger sample of 20 type ib - ic sne , using a generalization of their frequentist method . we find no significant evidence in either case of a correlation between type ib - ic sne and grbs , consistent with the very strong evidence against such a correlation that we find from our bayesian analysis .

quant-ph0211134

i

the generation of non - classical states of light has been central to the confirmation and elucidation of the quantum theory of radiation . today , such work takes on an added importance as part of the advancing field of deliberate quantum state engineering , motivated in part by applications in quantum communication and computation . for instance , deterministically generated single - mode single - photon states could greatly advance the efficiency and security of quantum cryptography.@xcite they are also a crucial resource for implementing a quantum computing scheme using linear optics , single - photon states , and photodetection @xcite . these immediate potential applications have spurred the development of devices which can produce single photons on demand , such as solid state devices which use the coulomb interaction between strongly confined electrons to produce single exciton states which then decay optically @xcite , or devices in which the fluorescence from single , isolated and optically - pumped molecules is collected @xcite . the stream of pulses produced from each of these devices has been shown to contain either zero or one , but rarely more than one , photon per pulse , thus differing radically from a classical coherent - state pulse which would contain a poisson distribution of photon number . furthermore , while these recent devices all produce fluorescence from a single optical emitter on - demand , none outputs this fluorescence into a practical single mode of the optical field . it has been shown recently that the effects of cavity quantum electrodynamics ( cqed ) can in principle be used to overcome this limitation and produce single - mode single photons on demand @xcite . in such a scheme , a single three - level atom is induced to fluoresce with high probability into a single resonant mode of a high - finesse optical cavity . experimental evidence for such cavity - induced raman transitions has been obtained @xcite , and a variant of this scheme has very recently been used to generate a sequence of single photons @xcite . by creating a highly controlled , single - quantum - level interaction of atoms and light , cqed can be used quite generally to produce non - classical states of the electromagnetic field in a single cavity mode . in this paper , we analyze a particular desired function of a cqed device that goes beyond the production of single- photon states , namely , the deterministic production of a fock state of the electromagnetic field containing an exact number of photons ( @xmath0 ) . such non - classical states are of interest for fundamental tests and applications of the theories of quantum optics ( such as quantum state tomography , as performed recently on the single - photon state @xcite ) , as a resource for heisenberg - limited quantum measurements made possible by the production of two orthogonal @xmath0-photon states @xcite , and quite generally as a starting point for the controlled engineering of more complex quantum states . starting with a precisely counted number of @xmath0 atoms trapped in the confines of a high - finesse optical cavity , we consider a scheme in which a classical pump field is ramped up to induce deterministic raman emission into a single cavity mode by each of the trapped atoms , resulting in an optical field of exactly @xmath0 photons that are emitted from the cavity in a single pulse . the atom - cavity system is constrained to remain within a subspace of optically dark @xmath0-atom states , resulting in a high fidelity of production . the present scheme provides a generalization of that proposed for the production of single photons from single atoms @xcite and indicates a systematic route to generation of other non - classical states . several other theoretical and experimental works have discussed the use of high - finesse cavities for the quantum engineering of mesoscopic non - classical optical states . the possibility of producing both fock states and arbitrary coherent superpositions of these inside a cavity by exploiting adiabatic transfer of atomic ground - state zeeman coherences in single atoms was already explored in ref . @xcite . a scheme for producing an arbitrary quantum optical state using a single two - level atom in a high - finesse cavity has also been presented by law and eberly , based on the arbitrary real - time control of a classical pump field and the coupling to a cavity field @xcite . experimental evidence for fock states of a microwave cavity field has recently been obtained as a dynamical equilibrium for a stream of rydberg atoms passing through a micromaser @xcite . another approach toward the construction of a fock state was proposed in ref . @xcite in which a rydberg atom with a stark - tunable level splitting is used to transfer photons one - by - one from a classically - populated cavity field to another initially empty cavity field . initial experimental steps towards this goal have been recently demonstrated @xcite . in contrast to the schemes of refs.@xcite which require delicate temporal control of the atom - cavity coupling , our present scheme yields the desired @xmath0-photon state for quite arbitrary temporal profiles of the classical pump field . this is achieved through a rapid adiabatic passage which transfers the initial `` non - classical '' state of @xmath0 atoms to the non - classical state of @xmath0 photons within a short period of time . thus , the quantum nature of the photon field is already guaranteed by the initial state of the atoms trapped in an initially empty cavity . the initial conditions can be achieved by lowering a cloud of cold atoms into the cavity , and pulse control is then entirely contained in the time dependence of the ramping field . this avoids the need to make use of atomic motion in controlling the coupling to the cavity field , as was required in ref . @xcite , and is one of the key elements allowing _ deterministic _ production of @xmath0-photon states to be achieved . the number of atoms in the cavity can be determined by detection of excited state atoms at the single - atom level , as a result of the cavity - mediated shifts of atomic levels . such single - atom detection has already been demonstrated @xcite , and can be readily extended to larger numbers of atoms . consequently , the present scheme opens the way to deterministic generation of more complicated quantum states of light by first producing non - classical states of trapped atoms ( such as spin - squeezed states produced through interatomic interactions @xcite or by measurement @xcite ) , and then transferring that state onto the optical field using cqed . the remainder of the paper is constructed as follows . a brief review of the deterministic single - photon generation schemes of refs . @xcite is given in section [ sec : single ] , which establishes some common concepts with the present work . a discussion of the @xmath0-atom / cavity system in a single - mode external field follows in section [ sec : nphoton ] . we demonstrate here the existence of a family of optically - dark coupled @xmath0-atom / cavity states and show generally how adiabatic ramping of an external field can be used to generate @xmath0-photon emission from the cavity . detailed analysis of the energy spectrum of the closed @xmath0-atom / cavity system as a function of the ramp time provides estimates of the populations in the bright states and also leads to analytic estimates of the energy gap required for limiting adiabatic state transfers . in section [ sec : open ] we then present analysis of the cavity decay responsible for the @xmath0-photon emission , treating in detail the effects of spontaneous emission and non - adiabaticity on the output states . we obtain analytic estimates of error rates deriving from these contributions that scale linearly in the total number of atoms , resulting in a constant relative error in the output @xmath0-photon states and guaranteeing production of an @xmath0-photon state with high fidelity . in section [ sec : quantumtraj ] we present numerical simulations of the open system using the quantum jump approach . these numerical calculations are used to explore the sensitivity of the scheme to critical experimental parameters , as well as to explore the limits of our analytical estimates of the error bounds . finally , in section [ sec : conclusions ] we summarize and indicate directions for further work and for experimental implementation .

the method applies an external laser pulse that generates an-photon output state while adiabatically keeping the atom - cavity system within a subspace of optically dark states . we present analytical estimates of the error due to amplitude leakage from these dark states for general , and compare it with explicit results of numerical simulations for . the method is shown to provide a robust source of-photon states under a variety of experimental conditions and is suitable for experimental implementation using a cloud of cold atoms magnetically trapped in a cavity . the resulting-photon states have potential applications in fundamental studies of non - classical states and in quantum information processing .

we present a scheme for the deterministic generation of-photon fock states from three - level atoms in a high - finesse optical cavity . the method applies an external laser pulse that generates an-photon output state while adiabatically keeping the atom - cavity system within a subspace of optically dark states . we present analytical estimates of the error due to amplitude leakage from these dark states for general , and compare it with explicit results of numerical simulations for . the method is shown to provide a robust source of-photon states under a variety of experimental conditions and is suitable for experimental implementation using a cloud of cold atoms magnetically trapped in a cavity . the resulting-photon states have potential applications in fundamental studies of non - classical states and in quantum information processing .

0903.1731

i

the galaxy populations of clusters are dominated by galaxies of early morphological type , ellipticals and s0s , which form a tight color magnitude relation ( cmr ) or ` red sequence ' . for decades , this relation was interpreted as evidence that the stars in early type galaxies in clusters are uniformly old , being formed at redshift @xmath15 , with the slope of the relation being primarily due to a mass - metallicity relation @xcite . the alternative interpretation of the cmr as being predominantly an age sequence was conclusively ruled out by observations of clusters at @xmath16 , which showed that the slope of the cmr evolves little with redshift @xcite . a number of studies of clusters conducted with the _ hubble space telescope _ have shown that the cmr of elliptical galaxies remains well established at progressively higher redshifts ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , at least up to @xmath17 @xcite . the only study to date of the cmr in a cluster at @xmath18 is consistent with this picture @xcite . measurements of the intrinsic scatter about the cmr can be used to constrain the ages of the constituent stellar populations of cluster early type galaxies , and indicate that major epoch of star formation in clusters was completed at @xmath19 ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? studies of the fundamental plane of elliptical galaxies up to high redshift similarly indicate that the bulk of stellar populations in elliptical galaxies were formed at @xmath19 ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? these observations are consistent with a simple formation scenario for elliptical galaxies , in which they formed the bulk of their stellar mass in a single event at high redshift , and evolved passively thereafter . however , the latest semi - analytic models of galaxy formation , constructed within the hierarchical formation paradigm , are also able to successfully reproduce the old ages of stellar populations in elliptical galaxies @xcite . recent observations over a wide range in redshift in both clusters and the field have revealed that star formation appears to be completed earlier in higher mass galaxies than in low mass galaxies , a phenomenon dubbed ` downsizing ' @xcite . in color - magnitude diagrams of high redshift clusters , this effect manifests itself as a deficit of faint galaxies on the red sequence in comparison to clusters observed at lower redshift ( e.g. * ? ? ? * ; * ? ? ? * ) , and may have an environmental dependence in the sense that the faint end of the cmr is populated at earlier times in denser regions , such as in the cluster cores , compared to low density regions such as groups ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? this could be explained qualitatively by a scenario in which the faint end of the red sequence is being built up by the transformation of star forming , spiral galaxies into passively evolving s0s as redshift increases . up to @xmath20 , studies of magnitude - limited samples of cluster galaxies have revealed that the elliptical galaxy fraction within clusters is found to remain roughly constant , while the fraction of s0 galaxies decreases , with a corresponding increase in the fraction of spiral and irregular galaxies @xcite . when considering stellar mass - limited samples , it has been found that the fraction of massive , early type galaxies as a whole remains roughly constant , at least up to @xmath21 @xcite . this suggests that the much stronger evolution seen in magnitude - limited samples is dominated by fainter , lower mass ( sub-@xmath22 in the galaxy stellar mass function ) galaxies . it should be noted that at the current time the evidence for downsizing within the centers of rich clusters is still somewhat contentious ( @xcite ; @xcite ) . in this paper , we present a study of the galaxy morphologies and color magnitude relation in xmmxcs j@xmath0 at @xmath1 @xcite , the most distant x - ray selected galaxy cluster currently known . to date , only five other spectroscopically confirmed clusters are known at @xmath23 , xmmu j@xmath24 at @xmath25 , discovered serendipitously with _ xmm - newton _ @xcite ; three clusters at @xmath26 from the irac shallow cluster survey ( iscs ; * ? ? ? * ; * ? ? ? * ) ; and the @xmath27 cluster j@xmath28 , discovered by the _ spitzer _ adaptation of the red - sequence cluster survey ( sparcs ; * ? ? ? j@xmath0 was discovered as part of the ongoing optical follow up campaign to the _ xmm _ cluster survey ( xcs ; * ? ? ? * ) , which has the primary aim of constraining the cosmological parameters through measuring the evolution of the cluster mass function with redshift . predictions for the expected cosmological constraints that are expected to be achieved by the full survey can be found in @xcite . j@xmath0 has x - ray luminosity @xmath29 ergs s@xmath30 , temperature @xmath31 kev @xcite , and velocity dispersion @xmath32 km s@xmath30 @xcite . there is mild evidence that the cluster velocity distribution is bimodal , which , if confirmed by further spectroscopic observations , would indicate that the cluster is undergoing a merger close to the line of sight @xcite . the structure of this paper is as follows . we begin by describing the observations and data reduction in [ s_observationsdatareduction ] . in [ s_analysis ] , we describe our photometric measurements , morphological classification , and photometric redshift selection of the cluster members . we present the morphological fractions , fits to the color magnitude relation , and inferred ages for the stellar populations of the early type galaxies in [ s_results ] . finally , we discuss our findings in comparison with previous work in [ s_discussion ] . we assume a concordance cosmology of @xmath33 , @xmath34 , and @xmath35 km s@xmath30 mpc@xmath30 throughout , where @xmath36 is the energy density associated with a cosmological constant .

we present a study of the morphological fractions and color magnitude relation in the most distant x - ray selected galaxy cluster currently known , xmmxcs j at , using a combination of optical imaging data obtained with the _ hubble space telescope _ in contrast to observations of some other clusters , we find a lack of very bright galaxies within the cluster .

we present a study of the morphological fractions and color magnitude relation in the most distant x - ray selected galaxy cluster currently known , xmmxcs j at , using a combination of optical imaging data obtained with the _ hubble space telescope _ advanced camera for surveys , and infrared data from the multi - object infrared camera and spectrograph , mounted on the 8.2 m _ subaru _ telescope . we find that the morphological mix of the cluster galaxy population is similar to clusters at . within the central 0.5 mpc , approximately% of the galaxies identified as likely cluster members are ellipticals or s0s ; and% are spirals or irregulars . therefore early type galaxies were already entrenched as the dominant galaxy population in at least some clusters approximately gyr after the big bang . we measure the color magnitude relations for the early type galaxies , finding that the slope in the relation is consistent with that measured in the coma cluster , some gyr earlier , although the uncertainty is large . in contrast , the measured intrinsic scatter about the color magnitude relation is more than three times the value measured in coma , after conversion to rest frame . from comparison with stellar population synthesis models , the intrinsic scatter measurements imply mean luminosity weighted ages for the early type galaxies in j of gyr , corresponding to the major epoch of star formation coming to an end at . we find that the cluster exhibits evidence of the ` downsizing ' phenomenon : the fraction of faint cluster members on the red sequence expressed using the dwarf - to - giant ratio ( dgr ) is within a radius of . this is consistent with extrapolation of the redshift evolution of the dgr seen in cluster samples at . in contrast to observations of some other clusters , we find a lack of very bright galaxies within the cluster .

0903.1731

c

we have conducted a study of the morphological fractions and color magnitude relation in the galaxy cluster xmmxcs j@xmath0 at @xmath1 . this is the first such study of an x - ray selected cluster at @xmath268 . we found : 1 . the brightest members of j@xmath0 have @xmath41 magnitudes corresponding to the expected value of @xmath269 in the galaxy luminosity function . this is significantly fainter than the brightest galaxies in the only other @xmath145 x - ray selected cluster studied to date , xmmu j@xmath24 at @xmath25 @xcite . the morphological fractions are @xmath270 , @xmath118 , @xmath119 , similar to other clusters at @xmath2 . thus , the dominant component of the galaxy population observed in clusters at low redshift was already in place @xmath5 gyr after the big bang . 3 . after transformation from @xmath6 to @xmath249 , the slope of the color magnitude relation is consistent with that of the coma cluster , implying little evolution over the last @xmath7 gyr , though the measurement uncertainty is large . in contrast , the intrinsic scatter about the color magnitude relation is more than three times the value measured in the coma cluster , after conversion from @xmath6 to @xmath249 . 4 . from comparison with stellar population models , the intrinsic scatter about the color magnitude relation implies mean luminosity weighted ages for the stellar populations of the early type galaxies in j@xmath0 of @xmath9 gyr , corresponding to the main epoch of star formation in these galaxies coming to an end at @xmath10 . comparison of the intercept of the color magnitude relation with passive evolution of the same stellar population models , calibrated relative to the coma cluster , yields consistent results . 5 . j@xmath0 shows evidence of the ` downsizing ' phenomenon : the red sequence dwarf - to - giant ratio for the cluster is @xmath11 within a radius of @xmath12 , although this is likely to be underestimated slightly in comparison to other studies due to the depth of our photometry . this is consistent with extrapolation of the redshift evolution of the dgr measured from cluster samples at @xmath13 within the large uncertainties . we thank the referee for a number of suggestions that improved the clarity of this paper . this work is based in part on data collected at the subaru telescope , which is operated by the national observatory of japan , and _ xmm_-newton , an esa science mission funded by contributions from esa member states and from nasa . we thank ichi tanaka for the development of the ` mcsred ` package used to reduce the moircs data . we acknowledge financial support from the south african national research foundation , the uk science and technology facilities council , and the university of sussex physics & astronomy department . financial support for this work was also provided by nasa through program go-10496 from the space telescope science institute , which is operated by aura , inc . , under nasa contract nas 5 - 26555 . this work was also supported in part by the director , office of science , office of high energy and nuclear physics , of the u.s . department of energy under contract no . ac02 - 05ch11231 , as well as a jsps core - to - core program `` international research network for dark energy '' and by jsps research grant 20040003 . this work was performed under the auspices of the u.s . department of energy by lawrence livermore national laboratory in part under contract w-7405-eng-48 and in part under contract de - ac52 - 07na27344 . the authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of mauna kea has always had within the indigenous hawaiian community ; we are fortunate to have the opportunity to conduct observations from this mountain . cccccccc @xmath6 & 22.5 & 19 & @xmath271 & @xmath272 & @xmath273 & @xmath274 & @xmath275 + @xmath42 & 21.5 & 16 & @xmath276 & @xmath277 & @xmath278 & @xmath279 & @xmath280 + @xmath6 & 24.0 & 34 & @xmath281 & @xmath282 & @xmath283 & @xmath284 & @xmath285 + @xmath42 & 23.0 & 36 & @xmath286 & @xmath287 & @xmath288 & @xmath289 & @xmath290 + cccccc @xmath6 & bc03 & @xmath174 & @xmath291 & @xmath292 & @xmath293 + @xmath6 & m05 & @xmath178 & @xmath294 & @xmath295 & @xmath296 + @xmath42 & bc03 & @xmath182 & @xmath297 & @xmath298 & @xmath299 + @xmath42 & m05 & @xmath186 & @xmath300 & @xmath301 & @xmath302 + @xmath6 & bc03 & @xmath303 & @xmath304 & @xmath305 & @xmath306 + @xmath6 & m05 & @xmath307 & @xmath308 & @xmath309 & @xmath310 + @xmath42 & bc03 & @xmath311 & @xmath312 & @xmath313 & @xmath314 + @xmath42 & m05 & & & & +

subaru _ telescope . therefore early type galaxies were already entrenched as the dominant galaxy population in at least some clusters approximately gyr after the big bang . we measure the color magnitude relations for the early type galaxies , finding that the slope in the relation is consistent with that measured in the coma cluster , some gyr earlier , although the uncertainty is large . in contrast , the measured intrinsic scatter about the color magnitude relation is more than three times the value measured in coma , after conversion to rest frame . from comparison with stellar population synthesis models , the intrinsic scatter measurements imply mean luminosity weighted ages for the early type galaxies in j of gyr , corresponding to the major epoch of star formation coming to an end at . we find that the cluster exhibits evidence of the ` downsizing ' phenomenon : the fraction of faint cluster members on the red sequence expressed using the dwarf - to - giant ratio ( dgr ) is within a radius of . this is consistent with extrapolation of the redshift evolution of the dgr seen in cluster samples at .

we present a study of the morphological fractions and color magnitude relation in the most distant x - ray selected galaxy cluster currently known , xmmxcs j at , using a combination of optical imaging data obtained with the _ hubble space telescope _ advanced camera for surveys , and infrared data from the multi - object infrared camera and spectrograph , mounted on the 8.2 m _ subaru _ telescope . we find that the morphological mix of the cluster galaxy population is similar to clusters at . within the central 0.5 mpc , approximately% of the galaxies identified as likely cluster members are ellipticals or s0s ; and% are spirals or irregulars . therefore early type galaxies were already entrenched as the dominant galaxy population in at least some clusters approximately gyr after the big bang . we measure the color magnitude relations for the early type galaxies , finding that the slope in the relation is consistent with that measured in the coma cluster , some gyr earlier , although the uncertainty is large . in contrast , the measured intrinsic scatter about the color magnitude relation is more than three times the value measured in coma , after conversion to rest frame . from comparison with stellar population synthesis models , the intrinsic scatter measurements imply mean luminosity weighted ages for the early type galaxies in j of gyr , corresponding to the major epoch of star formation coming to an end at . we find that the cluster exhibits evidence of the ` downsizing ' phenomenon : the fraction of faint cluster members on the red sequence expressed using the dwarf - to - giant ratio ( dgr ) is within a radius of . this is consistent with extrapolation of the redshift evolution of the dgr seen in cluster samples at . in contrast to observations of some other clusters , we find a lack of very bright galaxies within the cluster .

1206.6031

i

photoelectron spectroscopy is a widely used technique to analyze the electronic structure of complex systems @xcite . the advent of intense ultra - short laser sources has extended the range of applicability of this technique to a vast variety of non - linear phenomena like high - harmonic generation , above - threshold ionization ( ati ) , bond softening and vibrational population trapping @xcite . furthermore , it turned attosecond time - resolved pump - probe photoelectron spectroscopy into a powerful technique for the characterization of excited - states dynamics in nano - structures and biological systems @xcite . angular - resolved ultraviolet photoelectron spectroscopy is by now established as a powerful technique for studying geometrical and electronic properties of organic thin films @xcite . time - resolved information from streaking spectrograms @xcite , shearing interferograms @xcite , photoelectron diffraction @xcite , photoelectron holography @xcite , etc . hold the promise of wavefunction reconstruction together with the ability to follow the ultrafast dynamics of electronic wave - packets . clearly , to complement all these experimental advances , and to help to interpret and understand the wealth of new data , there is the need for ab - initio theories able to provide ( time - resolved ) photoelectron spectra ( pes ) and photoelectron angular distributions ( pad ) for increasingly complex atomic and molecular systems subject to arbitrary perturbations ( laser intensity and shape ) . photoelectron spectroscopy is a general term which refers to all experimental techniques based on the photoelectric effect . in photoemission experiments a light beam is focused on a sample , transferring energy to the electrons . for low light intensities an electron can absorb a single photon and escape from the sample with a maximum kinetic energy @xmath0 ( where @xmath1 is the photon angular frequency and @xmath2 the first ionization potential of the system ) while for high intensities electron dynamics can be interpreted considering a three - step model @xcite . this model provides a semiclassical picture in terms of ionization followed by free electron propagation in the laser field with return to the parent ion , and rescattering . such rescattering processes are the source of many interesting physical phenomena . in the case of long pulses , for instance , multiple photons can be absorbed resulting in emerging kinetic energies of @xmath3 ( where @xmath4 is the number of photons absorbed , @xmath5 is the ponderomotive energy and @xmath6 the electric field amplitude ) forming the so called ati peaks in the resulting photoelectron spectrum . in all cases the observable is the escaping electron momentum measured at the detector . in general , the interaction between electrons in an atom or molecule and a laser field is difficult to treat theoretically , and several approximations are usually performed . clearly , a full many - body description of pes is prohibitive , except for the case of few ( one or two ) electron systems @xcite . as a consequence , the direct solution of the time dependent schrdinger equation ( tdse ) in the so - called single - active electron ( sae ) approximation is a standard investigation tool for many strong - field effects in atoms and dimers and represents the benchmark for analytic and semi - analytic models @xcite . perturbative approaches based on the standard fermi golden rule are usually employed . for weak lasers , plane wave methods @xcite and the independent atomic center approximation @xcite have been applied , while in the strong field regime , floquet theory , the strong - field approximation @xcite and semiclassical methods @xcite are routinely used . from a numerical point of view , it would be highly desirable to have a pes theory based on time - dependent density functional theory ( tddft ) @xcite where the complex many - body problem is described in terms of a fictitious single - electron system . for a given initial many body state , tddft maps the whole many - body problem into the time dependence of the density from which all physical properties can be obtained . the method is in principle exact , but in practice approximations have to be made for the unknown exchange - correlation functional as well as for specific density - functionals providing physical observables . this latter issue is much less studied than the former , and to the best of our knowledge a formal derivation of momentum - resolved pes from the time dependent density has not been performed up to now . in any case , several works were published addressing the problem of single and multiple ionization processes within tddft . for example , ionization rates were calculated for atoms and molecules @xcite , and tddft with the sampling point method ( spm ) has been employed in the study of pes and pad for sodium clusters @xcite . in this work , besides presenting a formal derivation of a photoelectron orbital functional , we report on a new and physically sound scheme to compute pes of interacting electronic systems in terms of the time - dependent single electron kohn - sham ( ks ) wavefunctions . the scheme relies on geometrical considerations and is based on a splitting technique @xcite . the idea is based on the of partitioning of space in two regions ( see fig . [ fig : geometrical_scheme ] below ) : in the inner region , the ks wave function is obtained by solving the tddft equations numerically ; in the outer region , electrons are considered as free particles , the coulomb interaction is neglected , and the wavefunction is propagated analytically with only the laser field . electrons flowing from the inner region to the outer region are recorded and coherently summed up to give the final result . in addition to the adaptation of the traditional splitting procedure to tddft , we propose a novel scheme where electrons can seamlessly drift from one region to the other and spurious reflections are greatly suppressed . this procedure allows us to reduce considerably the spatial extent of the simulation box without damaging the accuracy of the method . the rest of this article is organized as follows . the formalism for describing photoelectrons in tddft is delineated in sect . [ sec : theory ] . in order to make contact with the literature , we first give a brief introduction to the state - of - the - art for the ab - initio calculation of pes for atomic and molecular systems . in sect . [ sub : phase - space_interpretation ] we introduce the geometrical approach in the context of quantum phase - space . the phase - space approach is then derived in the case of effective single - particle theories like tddft in sect . [ sub : phase_space_tddft ] . in sect . [ sub : the_mask_method ] we introduce the mask method , an efficient propagation scheme based on space partitioning . three applications of the mask method are presented in sect . [ sec : applications ] . one application deals with the hydrogen atom and illustrates the different mask methods in a simple one - dimensional model also in comparison with the sampling point method @xcite . the above threshold ionization of three - dimensional hydrogen is examined and compared with values from the literature . in the second application we illustrate pads from randomly oriented nitrogen molecules in a strong near - infrared ultra - short laser pulse . comparison with the experiment and molecular strong - field approximation is discussed @xcite . the third application of the method regards helium-(i ) ( wavelength 58 nm ) pads for oriented carbon monoxide and benzene . results are discussed in comparison with the plane wave approximation . finally , in sect . [ sec : conclusions ] we discuss the results and present the conclusions . all our numerical calculations were performed with the real - time , real - space tddft code ` octopus ` @xcite , freely available under the gnu public license . atomic units are used throughout unless otherwise indicated .

we present a time - dependent density - functional method able to describe the photoelectron spectrum of atoms and molecules when excited by laser pulses . this computationally feasible scheme is based on a geometrical partitioning that efficiently gives access to photoelectron spectroscopy in time - dependent density - functional calculations . by using a geometrical approach the approach is validated by comparison with results in the literature and exact calculations .

we present a time - dependent density - functional method able to describe the photoelectron spectrum of atoms and molecules when excited by laser pulses . this computationally feasible scheme is based on a geometrical partitioning that efficiently gives access to photoelectron spectroscopy in time - dependent density - functional calculations . by using a geometrical approach , we provide a simple description of momentum - resolved photoemission including multi - photon effects . the approach is validated by comparison with results in the literature and exact calculations . furthermore , we present numerical photoelectron angular distributions for randomly oriented nitrogen molecules in a short near infrared intense laser pulse and helium-(i ) angular spectra for aligned carbon monoxide and benzene . ,

0809.1326

i

the history of our universe is largely unknown between the surface of last scattering ( @xmath0 ) down to a redshift of about 6 . because of the dearth of radiating sources and the fact that we know very little about this epoch , it is often referred to as the `` dark ages '' . theoretical models suggest that around redshifts 10 20 , the first sources of radiation appeared that subsequently reionized the universe . two different experiments provide the bounds for this epoch of reionization ( eor ) ; the high polarization component at large spatial scales of the temperature - electric field ( te ) cross - polarization mode of the cosmic microwave background ( cmb ) providing the upper limit for the redshift at @xmath1 @xcite and the rapid increase in the lyman-@xmath2 optical depth towards redshift 6 , observed in the spectrum of high redshift quasars @xcite , the lower limit . although the redshifted 21 cm hyperfine transition of hydrogen was proposed as a probe to study this epoch decades ago @xcite , the technological challenges to make these observations possible are only now being realised . in the meantime , theoretical understanding of the eor has improved greatly @xcite . over the past few years there have been considerable efforts in simulating the 21 cm signal from the epoch of reionization . almost all of the methods employed in simulating the 21 cm involve computer intensive full 3-d radiative transfer calculations @xcite . theories predict that the process of reionization is complex and sensitively dependent on many not - so - well - known parameters . although stars may be the most favoured of reionization sources , the role of mini - quasars ( miniqsos ) , with the central black hole mass less than a few million solar masses , are debated @xcite . even if the nature of the sources of radiation would be relatively well constrained , there are a number of `` tunable '' parameters like the photon escape fraction , masses of these first sources , and so on , that are not well constrained . in a couple of years , next generation radio telescopes like lofar and mwa will be tuned to detect the 21 cm radiation from the eor . although the designs of these telescopes are unprecedented , the prospects for successfully detecting and mapping neutral hydrogen at the eor critically depends on our understanding of the behaviour and response of the instrument , the effect of diffuse polarized galactic & extra - galactic emission , point source contamination , ionospheric scintillations , radio frequency interference ( rfi ) and , not least , the characteristics of the desired signal . a good knowhow of the above phenomena would enable us to develop advanced signal processing / extraction algorithms , that can be efficiently and reliably implemented to extract the signal . in order to test and confirm the stability and reliability of these algorithms , it is imperative that we simulate , along with all the effects mentioned above , a large range of reionization scenarios . [ fig : bigpic ] shows the basic building blocks of the simulation pipeline being built for the lofar - eor experiment . this paper basically constitutes the first block , i.e. , simulation of the cosmological 21 cm eor signal . this then passes through a sequence of blocks like the foreground simulation @xcite , instrument response and extraction ( lambropoulous et al . , _ in prep _ ) . the extracted signal is then compared with the original signal to quantify the performance of the extraction scheme . this process needs to be repeated for various reionization scenarios to avoid any bias the extraction scheme would have if only a subsample of all possible signal characteristics were used . simulating observing windows as large as the field of view ( fov ) of lofar ( @xmath3 ) and for frequencies corresponding to redshift 6 to 12 is a daunting task for conventional radiative transfer codes because of multiple reasons such as a requirement for high dynamic range in mass for the sources of reionization , their large number towards the end of reionization and the size of the box which strains the memory of even the largest computer cluster . in order to facilitate the simulation of such large mock data sets for diverse reionization scenarios , we need to implement an approximation to these radiative transfer methods that mimic the `` standard '' simulations to good accuracy . it was clear from the onset that the details of the ionization fronts like its complex non - spherical nature will not be reproduced by the semi - analytical approach that we propose here . but the argument towards overlooking this discrepancy is that when the outputs of our semi - analytical approach and that of a radiative transfer code are passed through the machinery of the lofar - eor pipeline , they are experimentally indistinguishable . the reason being the filtering nature of the telescope s point spread function ( psf ) across the sky and the substantial bandwidth averaging along the frequency / redshift direction that is needed to recover the signal , smoothes out the structural details captured by codes . recently , several authors @xcite have proposed schemes to reduce the computational burden of generating relatively accurate 21 cm maps . these methods do fairly well , although there are some caveats , like for example the intergalactic medium ( igm ) ionization being treated as binary , i.e. , the igm is either ionized or neutral @xcite . although this might be the case for stellar - like sources , others with a power - law component could exhibit an effect on the igm wherein the ionizing front is extended and hence this assumption need not hold @xcite . added to this , the schemes presented in order to compute the 21 cm maps , make the assumption that the spin temperature of hydrogen , @xmath4 is much larger than the cmb temperature . towards the end of reionization ( @xmath5 ) this might very well be valid . but the dawn of reionization would see a complex spatial correlation of igm temperatures with the sources of radiation , its clustering and spectral energy distributions @xcite . in the current paper we have assumed that the spin temperature is coupled to the kinetic temperature and that they are much higher than the cmb temperature . at higher redshifts this need not be a valid assumption . the effects of heating by different types of radiative sources on the igm and the coupling ( both ly-@xmath2 and collisional ) between the spin and kinetic temperature will be simulated accurately in a follow - up paper _ thomas et al . , in prep _ , using the same scheme , but now applied to heating . in this paper we propose a method of post processing numerical simulations in order to rapidly generate realistic 21 cm maps . briefly , the algorithm consists of simulating the ionization fronts created by the `` first '' radiative sources for a range of parameters which include the power spectrum , source mass function and clustering . we then identify haloes in the outputs of n - body simulations and convert them to a photon count using semi - analytical prescriptions , or using the photon count derived from a smoothed particle hydrodynamics ( sph ) simulation . depending on the photon count and the spectrum , we embed a sphere around the centre - of - mass ( com ) of the halo whose radial profile matches that of a profile from the table created by the 1-d radiative transfer code of @xcite . appropriate operations are carried out to conserve photon number . since , the basic idea is to expand bubbles around locations of the sources of radiation , we call this method bears ( bubble expansion around radiative sources ) . for the sake of brevity and comparison with full radiative transfer codes , we restrict ourselves to monochromatic radiative transfer with a fixed temperature . a following paper will include a full spectrum along with the temperature evolution . the results of our semi - analytic scheme will be compared to those obtained with the full monte carlo radiative transfer code crash @xcite . in [ sec : simulations ] we describe the various steps involved in implementing the bears algorithm on the outputs of n - body simulations . we describe the specifications of the n - body simulations , the 1-d radiative transfer code used to produce the catalogue of ionization profiles , the algorithm employed to embed the sources and finally an illustrative example of the procedure to correct for the overlap of ionized bubbles . in [ sec : comparison ] the fully cosmological radiative transfer code crash is summarized and the results of its qualitative and statistical comparison with bears are discussed . [ sec : datacube ] describes the method of generating the cube with maps of the brightness temperature ( @xmath6 ) at all the frequencies that will be observed by an eor experiment . in [ sec : starsvquasars ] we use the simulation of the cube , with maps of the sky at different frequencies , to study the difference between two popular sources of reionization , i.e. , stars and quasars . these maps in the cube are then filtered through the lofar antenna response to output the final data cube in [ sec : instrumental ] . finally in [ sec : conclusions ] we summarize our results and outline further improvements that need to be made in our approach in order to start exploring the large parameter space involved in reionization studies .

we present an efficient method to generate large simulations of the epoch of reionization ( eor ) without the need for a full 3-dimensional radiative transfer code . large dark - matter - only simulations are post - processed to produce maps of the redshifted 21 cm emission from neutral hydrogen . dark matter haloes are embedded with sources of radiation whose properties are either based on semi - analytical prescriptions or derived from hydrodynamical simulations . these sources could either be stars or power - law sources with varying spectral indices . the efficiency with which these maps are created allows us to span the large parameter space typically encountered in reionization simulations . we generate a contiguous observational cube spanning redshift 6 to 12 and use these simulations to study the differences in the reionization histories between stars and quasars . statistics performed on this mock data set shed light on possible observational strategies for lofar . [ firstpage ] quasars : general cosmology : theory observation diffuse radiation radio lines : general .

we present an efficient method to generate large simulations of the epoch of reionization ( eor ) without the need for a full 3-dimensional radiative transfer code . large dark - matter - only simulations are post - processed to produce maps of the redshifted 21 cm emission from neutral hydrogen . dark matter haloes are embedded with sources of radiation whose properties are either based on semi - analytical prescriptions or derived from hydrodynamical simulations . these sources could either be stars or power - law sources with varying spectral indices . assuming spherical symmetry , ionized bubbles are created around these sources , whose radial ionized fraction and temperature profiles are derived from a catalogue of 1-d radiative transfer experiments . in case of overlap of these spheres , photons are conserved by redistributing them around the connected ionized regions corresponding to the spheres . the efficiency with which these maps are created allows us to span the large parameter space typically encountered in reionization simulations . we compare our results with other , more accurate , 3-d radiative transfer simulations and find excellent agreement for the redshifts and the spatial scales of interest to upcoming 21 cm experiments . we generate a contiguous observational cube spanning redshift 6 to 12 and use these simulations to study the differences in the reionization histories between stars and quasars . finally , the signal is convolved with the lofar beam response and its effects are analyzed and quantified . statistics performed on this mock data set shed light on possible observational strategies for lofar . [ firstpage ] quasars : general cosmology : theory observation diffuse radiation radio lines : general .

1506.08439

i

lvy processes play a large rle in contemporary mathematical finance @xcite , but also in many areas of physics , see e.g. @xcite . a real valued lvy process is a stochastic process @xmath2 that has increments @xmath3 , @xmath4 , that are independent of the past . the increments are also stationary in the sense that the probability distribution of the increment only depends on the time difference @xmath5 . furthermore , @xmath6 and a stochastic continuity condition for @xmath7 holds , see e.g. @xcite . under the given conditions , the characteristic function of @xmath2 is given by the lvy khinchine representation @xmath8=e^{t\psi(k)}\ ] ] @xmath9 $ ] stands for the expected value . @xmath10 is a conditionally positive definite function @xcite that has the following representation in terms of the canonical triplet @xmath11 : @xmath12 @xmath13 are constants , @xmath14 , and the lvy measure @xmath15 is a positive measure on @xmath16 such that @xmath17 in eq . ( [ eqa : levyformula ] ) @xmath18 is the characteristic function of the set @xmath19 which takes the value @xmath20 on this set and @xmath21 otherwise . the calibration problem for lvy processes consists of the estimation of the canonical triplet @xmath11 given the observation @xmath22 of the process trajectory @xmath2 at some prescribed times @xmath23 , @xmath24 . for instance , @xmath2 could be the process of log - returns of some asset and @xmath23 could be the closing time of the @xmath25-th trading day ( historic low frequency data ) . as the @xmath25-th increment of the process @xmath26 has the same distribution as @xmath27 , if @xmath28 , from a statistical point of view this is equivalent to the @xmath29-fold independent observation of the terminal values @xmath27 at time @xmath0 . @xmath2 can also be understood as the solution to the stochastic differential equation ( sde ) of jump - diffusion type @xmath30 here @xmath31 is a standard brownian motion and @xmath32,a)\sim{\rm po}(\nu(a)\delta t)$ ] is the random counting measure of jumps of height in the set @xmath33 in the time interval @xmath34 $ ] . @xmath35 stands for the poisson distribution with intensity @xmath36 and @xmath37,a)=n((t , t+\delta t],a)-\nu(a)\delta t$ ] is the compensated or martingale jump measure for small jumps , where we require @xmath38 for some @xmath39 , see @xcite for further details . the calibration problem for lvy processes , respectively the solution of ( [ eqa : sde ] ) , unfortunately is ill posed : the collection of all lvy measures @xmath40 is infinite dimensional , while only @xmath29 observations are available . direct application of the maximum likelihood principle in this situation leads to severe over - fitting issues @xcite . in many applications , one chooses families of lvy measures @xmath41 that depend only on a finite dimensional parameter vector @xmath42 , see e.g. @xcite . furthermore , one often restricts to such parametrizations , where the density @xmath43 of the probability distribution of @xmath2 can be calculated explicitly or at low numerical cost . one then assumes that the true distribution of @xmath2 is inside the prescribed set and uses the maximum likelihood approach for calibration @xcite . this assumption might however not be justified and give rise to modelling errors . as a non - parametric alternative , one can use generic parametrizations for the density of the lvy measure @xmath15 that can be refined depending on the amount of data available . this gives rise to a hierarchy or sieve @xcite of maximum likelihood problems with a finite number of parameters . if a suitable finite parametrization has been chosen , it remains to solve the maximum likelihood estimate at a given level of parametrization . one also has to determine this level based on the quality and also stability of the fits obtained . the resulting densities can no longer be calculated analytically . also , solution of the maximum likelihood problem gives rise to high dimensional optimization problems . the maximum likelihood method requires a parametric representation of the probability density functions ( pdf ) . the pdf can however be obtained as a solution to the kolmogorov forward equation ( fokker planck equation ) . the parameters @xmath42 then enter in this equation via coefficients in the generator of the semigroup @xcite . if the lvy measure @xmath15 is not zero , the generator of both these equations does not only contain a 2nd order partial differential operator , but also an integral operator of convolution type . this places the model calibration problem in the framework of optimal control problems with partial integral differential equations ( pide ) constraints . indeed , we know that the kolmogorov forward equation is representative of a stochastic process described in terms of sdes such as that one of eq . ( [ eqa : sde ] ) , where the set of parametrization for the approximation of the pdf , would correspond to a set of controls of the stochastic dynamic equation , so that , jointly to the maximum likelihood problem , it corresponds to a stochastic optimal control problem . the classical way to deal with the optimal control of stochastic process is by the dynamic programming principle and the related hamilton - jacobi - bellman equation for stochastic processes @xcite . however , this problem has been recently framed as a constrained pde optimization problem , where the pde is the fokker - planck , i.e. kolmogorov forward , equation @xcite . following this framework , the solution of the maximum likelihood problem , i.e. the stochastic optimization , is found by solving the first order optimality conditions in a functional space , that is the optimality system consisting of two pides , named forward and backward ( or adjoint ) equations , plus an optimality condition . this optimality system can be numerically solved by a gradient - based iterative algorithm as follows . the kolmogorov forward equation has a set of control parameters in order to maximize the log - likelihood functional for its terminal value . these controls involve the kolmogorov backward equation ( adjoint equation ) with suitable terminal condition , corresponding to the log - likelihood functional . hence , given an initial approximation of the unknown parametrization , first solve the forward equation , then set up the terminal condition and solve the adjoint one . with both the forward and adjoint solutions , by using the optimality condition equation the gradient is computed . then with a descending gradient technique , such as a non linear conjugate gradient method , found a better approximation of the control parameters and repeat until the satisfying accuracy for the parametrization is found . since this maximum likelihood problem could have an high dimensional space ad a huge number @xmath29 of observations , a fast , stable and enough accurate numerical solver for the pide is required . in our case the kolmogorov forward equation is a pide of parabolic differential operator type . such kind of pides are , e.g. , investigated in the option pricing models as a generalization of the black - scholes equation . the first difficulty to numerically solve this equation is the integral . in fact , in the case of using a fully implicit method , it would lead to solve a dense system of equation , for this reason implicit - explicit ( imex ) or operator splitting methods can be applied to bypass this problem ( see @xcite ) . the solution of the kolmogorov forward equation is a probability density function that is non negative with constant integral over the domain . such properties must be owned from the discrete solution too . the chang - cooper ( cc ) is a non - negative and conservative numerical method that has been used to solve the classical fokker - planck equation @xcite . here , we use a numerical method that can be classified as imex , since we use the cc method with an implicit time difference scheme for the differential operators of our pide , and evaluate the integral operator at the previous time step solution , i.e. in an explicit way . we prove for the resulting numerical solver : conservativeness , non - negativity and stability in the @xmath1-norm . the numerical solver for the adjoint equation is obtained directly from the solver for the forward equation by using the `` discretize then optimize '' approach to the optimization problem . finally , we quote , that for related work with vanishing lvy measure see e.g. @xcite , and for estimation procedures based on non parametric approximations of the empirical characteristic function see e.g. @xcite . an approach based on the method of moments and asymptotic expansions of lvy densities can be found in @xcite . the article is organised as follows : in the following section [ sec : reg ] we describe the hierarchy , of estimation problems . we shall show that the estimation problems that can actually be solved numerically can come arbitrarily close , at increasing computational cost , to the fully general lvy estimation problem . we also show that the use of periodic boundary conditions in the kolmogorov equations can be understood in terms of mapping the original lvy process on the real line to a derived lvy process on the torus . in section [ sec : kol ] , we set up the maximum likelihood estimation problem for a given parametrization and derive kolmogorov s forward ( fokker - planck ) equation and its adjoint ( kolmogorov backward ) equation with terminal conditions set by the log - likelihood objective functional . this maximum likelihood estimation problem is solved in the framework of the fokker - planck optimal control of stochastic processes , as a constrained pde optimal control problem . in section [ sec : num ] the discretization for kolmogorov s equations and the optimal control scheme is derived following a chang - cooper and imex approach . in particular we prove the structural properties of the numerical solution , i.e. conservativeness , non - negativity and stability . section [ sec : cons ] gives numerical tests for the consistency of the proposed procedure based on simulated data . we propose to use akaike s information criterion ( aic ) @xcite to choose an adequate parametrization from the hierarchy of spline parametrizations for density of the lvy measure . three different tests are performed : we first fit data that are simulated from a given distribution within our hierarchy of lvy distributions . the fits obtained are shown to be of very good quality and aic - selection criterion reproduces almost the original parametrization . as a second test we fit simulated data from a bi - directional gamma process , i.e. the difference of two independent gamma processes @xcite , which is not inside one of the parametrizations of degree @xmath44 , but can be approximated by those . the bi - directional gamma process is augmented by a small diffusive component and projected to the torus . the aic selection criterion and the fitting results again reproduce the final distribution of this process rather adequately . as a final test , we select financial data from the german stock exchange dax in a period between april 1998 and march 2002 and consider daily log - returns over 1000 trading days . this period represents a rather stable period for the dax with an almost constant level of the volatility . after projection , the aic based method selects a six - parameter spline approximation of the lvy measure density . the resulting fits again give a decent reproduction of the empirical distribution . our conclusions and an outlook are given in the final section [ sec : out ] .

we present an optimal control approach to the problem of model calibration for lvy processes based on a non parametric estimation procedure . the calibration problem is of considerable interest in mathematical finance and beyond . calibration of lvy processes is particularly challenging as the jump distribution is given by an arbitrary lvy measure , which form a infinite dimensional space . in this work , we provide this by the optimal control of kolmogorov s forward equation for the probability density function ( fokker - planck equation ) . the first order optimality conditions are derived based on the lagrange multiplier technique in a functional space . we prove conditions for non - negativity and stability in the norm of the discrete solution . to set boundary conditions , we argue that any lvy process on the real line can be projected to a torus , where it again is a lvy process .

we present an optimal control approach to the problem of model calibration for lvy processes based on a non parametric estimation procedure . the calibration problem is of considerable interest in mathematical finance and beyond . calibration of lvy processes is particularly challenging as the jump distribution is given by an arbitrary lvy measure , which form a infinite dimensional space . in this work , we follow an approach which is related to the maximum likelihood theory of sieves . the sampling of the lvy process is modelled as independent observations of the stochastic process at some terminal time . we use a generic spline discretization of the lvy jump measure and select an adequate size of the spline basis using the akaike information criterion ( aic ) . the numerical solution of the lvy calibration problem requires efficient optimization of the log likelihood functional in high dimensional parameter spaces . we provide this by the optimal control of kolmogorov s forward equation for the probability density function ( fokker - planck equation ) . the first order optimality conditions are derived based on the lagrange multiplier technique in a functional space . the resulting partial integral - differential equations ( pide ) are discretized , numerically solved and controlled using scheme a composed of chang - cooper , bdf2 and direct quadrature methods . for the numerical solver of the kolmogorov s forward equation we prove conditions for non - negativity and stability in the norm of the discrete solution . to set boundary conditions , we argue that any lvy process on the real line can be projected to a torus , where it again is a lvy process . if the torus is sufficiently large , the loss of information is negligible . * msc ( 2010 ) : * 93e10 ( primary ) 49k20 , 60g51 , 62g05 ( secondary ) * key words : * optimal control of pide , kolmogorov equations , fokker - planck equation , lvy processes , non - parametric maximum likelihood method , akaike information criterion , financial data .

astro-ph0007296

i

the trojans are a distant group of asteroids dynamically linked to jupiter by a 1:1 mean motion resonance which causes them to librate about stable lagrangian equilibrium points located @xmath4 in front of ( l4 ) and behind ( l5 ) jupiter along its orbit . because trojans orbit far from the sun and also have low albedos , they suffer from a low discovery rate and hence are underrepresented among numbered asteroids . extrapolating from the identified trojan objects , shoemaker _ et al . _ ( 1989 ) estimate that the total trojan population contains nearly half as many asteroids as the main belt . the large number of trojans and their strong dynamical connection to jupiter make determining their origins an important goal ; by understanding the early history of the trojans , we may also gain insight into jupiter s formation and early evolution . clues about the origins of the trojan asteroids may be found in their current physical and orbital properties , which include the overlapping signatures of mechanisms which captured them into librating orbits , as well as processes which have contributed to the population s evolution over time . some distinctive characteristics of the current trojan asteroids include a small mean eccentricity of @xmath5 , a small mean libration amplitude of @xmath6 , and a large mean inclination of @xmath7 ( @xcite , @xcite ) . also , nearly twice as many asteroids have been observed librating about the l4 point as about the l5 point . this , however , may simply be the result of observational selection effects ( @xcite ) . there are many competing theories for the origin and evolution of the trojan asteroids . it has been suggested that the trojans may have originally been comets ( @xcite ) or near - jupiter planetesimals ( _ e.g. _ @xcite , @xcite ) . a number of mechanisms have been considered for capturing these objects into trojan orbits , including collisions between objects , drag forces , and mass accretion by jupiter . et al . _ ( 1989 ) theorized that collisional emplacement of fragments of near - jupiter planetesimals during the dispersion of the planetesimal swarm may have provided most of the trojan objects . more recently , numerical modeling of the collisional evolution of the trojan population ( marzari _ et al . _ 1997 ) has shown that collisions are largely responsible for shaping the current size distribution of the smaller trojans , as well as having caused the escape of some of the trojan objects into chaotic orbits . long - term numerical integrations by levison _ et al . _ ( 1997 ) have also shown that the trojan population is dynamically unstable and that dynamical diffusion has contributed and continues to contribute to the loss of trojan objects . various types of drag forces acting on jupiter and/or the trojan precursors have also been examined . kary and lissauer ( 1995 ) considered solar nebular gas drag . they showed numerically that gas drag could cause planetesimals to be captured into 1:1 resonance with a protoplanet . interestingly , they found that such capture is rare for planets on circular orbits , but quite common for planets with appreciable eccentricities . gas drag may also have played a significant role in evolving the trojan population into its present form , provided that the trojan precursors were captured before the dispersion of the solar nebula ( peale 1993 ) . yoder ( 1979 ) looked at the effects of dynamical friction during jupiter s dispersal of the planetesimal swarm , which caused a slight inward migration of jupiter . he argued that this migration would cause a decrease in the libration amplitudes of jupiter s trojan companions ( see , however , table i ) . the possibility that a change in jupiter s mass could be responsible for the capture of the trojan asteroids was investigated by rabe ( 1954 ) who argued analytically that a decrease in jupiter s mass could cause its satellites to move onto trojan orbits . more recently , marzari and scholl ( 1998 ) showed numerically that an increase in jupiter s mass could cause the capture of planetesimals into librating orbits . they used a proto - jupiter on a `` best guess '' orbit growing simultaneously with saturn over a period of @xmath8 or @xmath9 years , and found that a large fraction of the planetesimals initially on horseshoe orbits and a small percentage of those initially orbiting near the 1:1 resonance were captured into tadpole orbits . past changes in jupiter s mass have also long been considered as a potentially significant evolutionary mechanism for creating the current distribution of trojan asteroids ; however , attempts to predict the exact form of the effects of jupiter s growth on the trojans have thus far been contradictory . for an increase in jupiter s mass , rabe ( 1954 ) theorized that the trojan libration amplitudes would increase , horedt ( 1974a , 1974b , 1984 ) argued that they would not be appreciably affected , and yoder ( 1979 ) argued that they would decrease ( table i ) . in this paper , we focus on the changes which jupiter underwent early in its history . we investigate the significance of jupiter s mass growth and radial migration as trojan capture mechanisms and especially as mechanisms for evolving the trojan population . we focus on these two processes in isolation in order to fully characterize their behavior . other potentially important processes including gas drag , the gravity of other planets , and collisions amongst trojans are not considered here , because models which include all of these effects would have a large number of poorly - determined free parameters . for example , with gas drag , what is the gas density as a function of distance from the sun ? when and exactly how does jupiter form a gap in the gas distribution ? how sensitive are trojan asteroids to different gas drag models ? these questions are important and need to be studied in depth . there are many open questions like these in the full trojan formation problem , probably more than can be addressed in a single paper . accordingly , we have chosen to study individual processes first for later incorporation into a more general model . a strong advantage to this approach is that investigating individual processes in detail will ultimately lead to a deeper physical understanding of results from more complicated models . adopting this approach , we first present consistent analytic and numerical results which show the effects of jupiter s growth and radial migration on its trojan companions in the limit of a slowly - changing jupiter , thus settling the previous controversy . we then explore the working of these mechanisms for a wide range of timescales , initial trojan libration amplitudes , jupiter eccentricities , and asteroid eccentricities and inclinations .

we present analytic and numerical results which illustrate the effects of jupiter s accretion of nebular gas and the planet s radial migration on its trojan companions . key words : + asteroids , dynamics + celestial mechanics + jupiter + origin , solar system + resonances + astronomy department , university of maryland + heather j. fleming + astronomy department + university of maryland + college park , md 20742 - 2421 + tel : ( 301 ) 474 - 7582 + fax : ( 301 ) 314 - 9067 + e - mail : hcohen@astro.umd.edu + douglas p.

we present analytic and numerical results which illustrate the effects of jupiter s accretion of nebular gas and the planet s radial migration on its trojan companions . initially , we approximate the system by the planar circular restricted three - body problem and assume small trojan libration amplitudes . employing an adiabatic invariant calculation , we show that jupiter s thirty - fold growth from a core to its present mass causes the libration amplitudes of trojan asteroids to shrink by a factor of about 2.5 to of their original size . the calculation also shows that jupiter s radial migration has comparatively little effect on the trojans ; inward migration from 6.2 to 5.2 au causes an increase in trojan libration amplitudes of . in each case , the area enclosed by small tadpole orbits , if made dimensionless by using jupiter s semimajor axis , is approximately conserved . similar adiabatic invariant calculations for inclined and eccentric trojans show that jupiter s mass growth leaves the asteroid s eccentricities and inclinations essentially unchanged , while one au of inward migration causes an increase in both of these quantities by . numerical integrations confirm and extend these analytic results . we demonstrate that our predictions remain valid for trojans with small libration amplitudes even when the asteroids have low , but nonzero , eccentricities and inclinations and/or jupiter has an eccentricity similar to its present value . the integrations also show that trojans with large libration amplitudes , including horseshoe orbits , are even more strongly affected by jupiter s mass growth and radial migration than simple scaling from our analytic results would suggest . further , the numerical runs demonstrate that jupiter s predicted mass growth is sufficient to cause the capture of asteroids initially on horseshoe orbits into stable tadpole orbits . thus , if jupiter captured most of its trojan companions before or while it accreted gas , as seems probable , then jupiter s growth played a significant role in stabilizing trojan objects by systematically driving them to lower libration amplitudes . key words : + asteroids , dynamics + celestial mechanics + jupiter + origin , solar system + resonances + astronomy department , university of maryland + heather j. fleming + astronomy department + university of maryland + college park , md 20742 - 2421 + tel : ( 301 ) 474 - 7582 + fax : ( 301 ) 314 - 9067 + e - mail : hcohen@astro.umd.edu + douglas p. hamilton + astronomy department + university of maryland + college park , md 20742 - 2421 + tel : ( 301 ) 405 - 1548 + fax : ( 301 ) 314 - 9067 + e - mail : hamilton@astro.umd.edu + submitted to _ icarus _ : june 16 , 1999 + revised : + 41 pages + 13 figures and 2 tables + running head : origin of the trojan asteroids + corresponding author : + douglas p. hamilton + astronomy department + university of maryland + college park , md 20742 - 2421 + tel : ( 301 ) 405 - 1548 + fax : ( 301)314 - 9067 + e - mail : hamilton@astro.umd.edu +

astro-ph0007296

r

consider the planar circular restricted three - body problem , in which two massive bodies move about each other in circular orbits due to their mutual gravitation and a third body of infinitesimal mass moves in the orbital plane of the two massive objects . this system admits five equilibrium points where a test particle can have zero velocity and zero acceleration in the frame which corotates with the primary masses about their common center of mass ( danby 1988 ) . three of these points lie along the line through the two primaries and are unstable . the other two , l4 and l5 , lie at the tips of the equilateral triangles whose bases are the line connecting the primary masses ( see fig . 1 ) . these are called the triangular lagrangian equilibrium points and are stable to small oscillations so long as the mass ratio of the primaries , @xmath10 ( where @xmath11 and @xmath12 are the larger and smaller of the primary masses , respectively ) , satisfies @xmath13 ( @xcite ) . this condition is met for all sun - planet and planet - moon pairs in the solar system , with the exception of pluto and charon . the planar circular restricted three - body problem is a reasonable approximation for the system consisting of the sun , jupiter , and a trojan asteroid , since the asteroid s mass is insignificant in comparison to either jupiter or the sun , and jupiter s eccentricity is relatively small ( @xmath14 currently ) . if we make the further approximations that the trojan s oscillations about its equilibrium position are small and that the asteroid is on a nearly circular orbit , then , noting that @xmath15 where @xmath16 is the mass of the sun and @xmath17 is the mass of jupiter , the motion of the asteroid is well approximated by the equation @xmath18 ( @xcite ) , where @xmath19 is the difference between the mean longitudes of the asteroid and jupiter , @xmath20^{1/2 } \label{nj}\ ] ] is the mean motion of jupiter ( @xmath21 is jupiter s semimajor axis and @xmath22 is the gravitational constant ) , and an overdot signifies differentiation with respect to time . the observed librational motions of the trojan asteroids are well approximated by the solution of eq . [ tmotion ] , @xmath23 where @xmath24 @xmath25 is time , and @xmath26 and @xmath27 are constants . note that @xmath28 is the amplitude of the @xmath19 oscillations . the libration amplitude , @xmath26 , is defined to be the total angular extent of these oscillations ( see fig . 1 ) . equivalently , the system can be described by the hamiltonian : @xmath29 the canonical variables for this hamiltonian are @xmath30 and @xmath31 , so that @xmath32 , and @xmath33 reproduces the equation of motion ( eq . [ tmotion ] ) . when changes are made to this system ( _ e.g. _ mass growth of one of the primaries or the addition of an external drag force ) , the hamiltonian is no longer conserved . however , if the changes to the hamiltonian system are slow enough , it can be shown that the action , @xmath34 , is approximately conserved ( @xcite ) . such slow changes are called adiabatic changes , and @xmath35 is an adiabatic invariant . using the expressions for @xmath36 , @xmath37 , and @xmath19 above , we determine the action for the three - body system : @xmath38 where we have evaluated the integral by using the adiabatic approximation that @xmath21 , @xmath26 , and @xmath39 are constant over one libration period . the conservation of the action can be written in the useful form : @xmath40 where the subscripts @xmath41 and @xmath42 indicate the initial and final values of the variables , respectively . for radial migration of jupiter , we can find the resulting change in the trojan s libration amplitude directly from eq . [ analyticresult ] ; since changing @xmath21 has no effect on @xmath17 , the factor @xmath43 is equal to 1 . then , for a physically reasonable inward radial migration of jupiter from approximately 6.2 au to 5.2 au ( see section 4 ) , eq . [ analyticresult ] predicts an increase in the trojan s libration amplitude of only @xmath2 . determining the effects of jupiter s mass growth on the trojan s libration amplitude is a bit more subtle , since increasing @xmath17 may affect @xmath21 as well as @xmath26 . in order to determine how changing @xmath17 affects @xmath21 , we digress briefly to discuss a second adiabatic invariant calculation . if we consider the two - body system of jupiter and the sun moving about one another on elliptical orbits due to their mutual gravitation , we can calculate an invariant action for slow changes in the mass of either body . noting that , in this case , adiabatic means that changes to the system are negligible over one orbital period , we find @xmath44 this result was contemplated nearly one hundred years ago when strmgen ( 1903 ) considered what effect mass accretion by the earth would have on the orbit of the moon ( see also @xcite ) . for our case , the invariance of @xmath45 means that if the mass of either jupiter or the sun were slowly decreased , jupiter s orbit would drift outward . this effect is well known ( _ e.g. _ horedt 1984 ) and was observed recently in numerical simulations by duncan and lissauer ( 1998 ) in which the orbits of the outer planets were seen to expand as the mass of the sun was decreased to a small fraction of its original value . similarly , if either jupiter or the sun slowly accretes mass , jupiter s semimajor axis will decrease . note that eq . [ 2bconstant ] implies that adding a jovian mass of material to either jupiter or the sun produces the same change in the semimajor axis of the system . returning to our discussion of the effects of jupiter s mass growth on its trojan companions , we see from eq . [ 2bconstant ] that if we change the mass of jupiter adiabatically , the semimajor axis of jupiter s orbit will be altered according to @xmath46 substituting this into eq . [ analyticresult ] , we see the full effect which altering @xmath17 has on the trojan s libration amplitude : @xmath47 since @xmath48 , the second term in parentheses is very nearly equal to 1 , and the change in @xmath26 is given sufficiently accurately by eq . [ analyticresult ] if we simply take @xmath49 . we find that the growth of jupiter by gas accretion from a @xmath50 core to its present mass of @xmath51 causes @xmath26 to decrease to @xmath52 of its original value . thus , if librating trojan asteroids were already present when jupiter was a @xmath0 core , then the effects of jupiter s mass increase would be substantial and would dominate over the effects of its radial migration . the effect of jupiter s radial migration is comparable to its mass accretion only if the planet moves inward by a factor of @xmath53 , _ e.g. _ from 150 au to 5 au , substantially more than current theories predict . there has been some significant confusion in the literature about the effects of jupiter s mass growth on the libration amplitudes of its trojan companions ( see table i ) . our analytic result for the effects of jovian mass growth disagrees with the findings of rabe ( 1954 ) and horedt ( 1974a , 1974b , 1984 ) , but agrees exactly , in both direction and magnitude , with the conclusions of yoder ( 1979 ) . our prediction for the effects of jupiter s radial migration , however , disagrees with yoder s 1979 result ( see table i ) . statements in yoder _ et al . _ ( 1983 ) about the tidal evolution of the saturnian satellites janus and epimetheus , however , are inconsistent with yoder s 1979 calculations , but agree , at least in sign , with our radial migration results . in order to dispel this confusion , we carefully verify our analytic predictions with numerical simulations in sections 3 and 4 below . we can make further use of the two - body adiabatic invariant for the sun - jupiter system ( eq . [ 2bconstant ] ) to gain additional insight into the meaning of the three - body adiabatic invariant ( eq . [ taction ] ) . when @xmath26 and @xmath54 are both very small , the trojan asteroid orbit , viewed in the frame which corotates with jupiter , looks like a little ellipse centered on one of the lagrangian equilibrium points with the ratio of its semimajor to semiminor axis equal to @xmath55 ( murray and dermott 1999 ) . the area within this ellipse is @xmath56 for a small tadpole orbit , the libration amplitude times the semimajor axis of jupiter s orbit is approximately equal to the major axis of the ellipse ( @xmath57 ) . thus we can rewrite eq . [ area1 ] as @xmath58 where we have used the two- and three - body adiabatic invariants defined in eqs . [ 2bconstant ] and [ taction ] , respectively . so , we find : @xmath59 thus , the invariance of the action for the three - body system implies that the dimensionless area enclosed by a small - amplitude trojan orbit ( _ i.e. , _ the area enclosed by the trojan orbit divided by the square of jupiter s semimajor axis ) , remains constant for an adiabatic change to the system . for example , as jupiter accretes mass , the resulting change in @xmath21 is relatively small , so as @xmath26 decreases , the radial width of the trojan orbit must increase in order to keep the area nearly constant ( see fig . 1 ) . note , however , that the area within the tadpole orbit in fig . 1 is not strictly conserved because the libration amplitude of the tadpole is quite large . finally , we can use the two - body adiabatic invariant for the sun - jupiter system ( eq . [ 2bconstant ] ) to determine what effect changing the mass of the sun has on the libration amplitudes of jupiter trojans . the dependence of @xmath26 on @xmath16 is present in eq . [ analyticresult ] through the factor @xmath60 . we know from @xmath45 ( eq . [ 2bconstant ] ) that if the mass of the sun is altered adiabatically , @xmath21 will change according to @xmath61 combining this with eq . [ analyticresult ] , we find @xmath62 for an adiabatic change in @xmath16 . thus , slowly increasing the mass of the sun increases the libration amplitude of the trojan , which is the opposite of the effect on @xmath26 caused by adding mass to jupiter . additional adiabatic invariant calculations determine the effects of changing jupiter s mass and semimajor axis on a trojan asteroid s eccentricity , @xmath63 , and inclination , @xmath64 . for the case when @xmath65 , we approximate the orbit of the trojan as an inclined circle . then , the motion of the asteroid in the @xmath66-direction can be well represented by simple harmonic motion with a restoring force equal to the sum of the @xmath66-components of the gravitational forces of the sun and jupiter acting on the asteroid . if we assume that the asteroid s inclination and libration amplitude are small , the distances between jupiter , the asteroid , and the sun are all approximately equal to @xmath21 . then , the restoring force per unit mass acting on the asteroid is @xmath67 where @xmath66 is the distance of the trojan asteroid above the plane of jupiter s orbit . notice that the vertical oscillation frequency is the same as jupiter s orbital frequency ( eq . [ nj ] ) . the hamiltonian for the vertical motion is @xmath68 which has canonical variables @xmath69 and @xmath70 . as in section 2.1 , for an adiabatic change to the system , the action is conserved . noting that here adiabatic means that changes to the system are negligible over one orbital period , we find @xmath71 where we have used the relation @xmath72 and integrated over a full orbital period . from this result , we see that if an external force adiabatically changes the semimajor axis of jupiter s orbit about the sun , the inclination of the trojan will change according to the relation @xmath73 if instead the mass of jupiter or the sun is varied , eq . [ inclconst ] tells us that some combination of @xmath64 and @xmath21 must change to keep the action constant . we determine how the variation is shared between @xmath64 and @xmath21 by using the invariant action for the two - body sun - jupiter system , @xmath45 ( eq . [ 2bconstant ] ) . dividing eq . [ inclconst ] by eq . [ 2bconstant ] , we find @xmath74 for an adiabatic change in either @xmath17 or @xmath16 . the adiabatic calculation for an eccentric asteroid orbit parallels that for an inclined orbit , however the radial oscillation frequency is given by @xmath75^{1/2 } \label{rfreq}\ ] ] ( murray and dermott 1999 , page 94 ) rather than by eq . [ nj ] . accordingly , the action , evaluated for small eccentricities has the form @xmath76 and @xmath63 will respond to an adiabatic change in @xmath21 according to the relation @xmath77 this result is in agreement with analytic work by gomes ( 1997 ) who showed that @xmath63 would increase when @xmath21 was decreased . for variations in @xmath16 and/or @xmath17 , we combine eqs . [ 2bconstant ] and [ jecc ] , and find @xmath78 thus an increase in jupiter s mass should lead to a slight increase in a trojan asteroid s eccentricity . in summary we find , using the invariance of the action for adiabatic changes to the sun - jupiter and sun - jupiter - trojan systems , that if the semimajor axis of jupiter is decreased , the asteroid s libration amplitude ( eq . [ analyticresult ] ) , eccentricity ( eq . [ eccaresult ] ) , and inclination ( eq . [ inclaresult ] ) will all increase . we find further that if we increase jupiter s mass , @xmath21 will decrease ( eq . [ amj ] ) and the trojan s libration amplitude will decrease ( eq . [ libampmj ] ) , its eccentricity will increase slightly ( eq . [ eccmresult ] ) , and its inclination will remain unchanged ( eq . [ inclmresult ] ) . finally , if the sun s mass is increased , @xmath21 will be decreased ( eq . [ ams ] ) and the asteroid will be dragged inward with jupiter , @xmath26 will increase by the same amount it would were @xmath21 altered by an external force ( eq . [ libampms ] ) , @xmath63 will decrease slightly ( eq . [ eccmresult ] ) and @xmath64 will not change ( eq . [ inclmresult ] ) . these results are also summarized in table ii .

hamilton + astronomy department + university of maryland + college park , md 20742 - 2421 + tel : ( 301 ) 405 - 1548 + fax : ( 301 ) 314 - 9067 + e - mail : hamilton@astro.umd.edu + submitted to _ icarus _ : june 16 , 1999 + revised : + 41 pages + 13 figures and 2 tables + running head : origin of the trojan asteroids + corresponding author : + douglas p. hamilton + astronomy department + university of maryland + college park , md 20742 - 2421 + tel : ( 301 ) 405 - 1548 + fax : ( 301)314 - 9067 + e - mail : hamilton@astro.umd.edu +

we present analytic and numerical results which illustrate the effects of jupiter s accretion of nebular gas and the planet s radial migration on its trojan companions . initially , we approximate the system by the planar circular restricted three - body problem and assume small trojan libration amplitudes . employing an adiabatic invariant calculation , we show that jupiter s thirty - fold growth from a core to its present mass causes the libration amplitudes of trojan asteroids to shrink by a factor of about 2.5 to of their original size . the calculation also shows that jupiter s radial migration has comparatively little effect on the trojans ; inward migration from 6.2 to 5.2 au causes an increase in trojan libration amplitudes of . in each case , the area enclosed by small tadpole orbits , if made dimensionless by using jupiter s semimajor axis , is approximately conserved . similar adiabatic invariant calculations for inclined and eccentric trojans show that jupiter s mass growth leaves the asteroid s eccentricities and inclinations essentially unchanged , while one au of inward migration causes an increase in both of these quantities by . numerical integrations confirm and extend these analytic results . we demonstrate that our predictions remain valid for trojans with small libration amplitudes even when the asteroids have low , but nonzero , eccentricities and inclinations and/or jupiter has an eccentricity similar to its present value . the integrations also show that trojans with large libration amplitudes , including horseshoe orbits , are even more strongly affected by jupiter s mass growth and radial migration than simple scaling from our analytic results would suggest . further , the numerical runs demonstrate that jupiter s predicted mass growth is sufficient to cause the capture of asteroids initially on horseshoe orbits into stable tadpole orbits . thus , if jupiter captured most of its trojan companions before or while it accreted gas , as seems probable , then jupiter s growth played a significant role in stabilizing trojan objects by systematically driving them to lower libration amplitudes . key words : + asteroids , dynamics + celestial mechanics + jupiter + origin , solar system + resonances + astronomy department , university of maryland + heather j. fleming + astronomy department + university of maryland + college park , md 20742 - 2421 + tel : ( 301 ) 474 - 7582 + fax : ( 301 ) 314 - 9067 + e - mail : hcohen@astro.umd.edu + douglas p. hamilton + astronomy department + university of maryland + college park , md 20742 - 2421 + tel : ( 301 ) 405 - 1548 + fax : ( 301 ) 314 - 9067 + e - mail : hamilton@astro.umd.edu + submitted to _ icarus _ : june 16 , 1999 + revised : + 41 pages + 13 figures and 2 tables + running head : origin of the trojan asteroids + corresponding author : + douglas p. hamilton + astronomy department + university of maryland + college park , md 20742 - 2421 + tel : ( 301 ) 405 - 1548 + fax : ( 301)314 - 9067 + e - mail : hamilton@astro.umd.edu +

astro-ph0007296

c

we have shown with both a simple adiabatic calculation and numerical simulations , that slow changes to the mass and semimajor axis of jupiter cause the trojan libration amplitude to vary according to the relation : @xmath148 for trojans with small libration amplitudes , small eccentricities , and small inclinations , and jupiter with a small eccentricity . for inclined and eccentric trojan objects , we find that jupiter s mass growth does not significantly affect either the trojan s eccentricity or inclination ; however , jupiter s radial migration causes a change in the free component of both of these quantities by a factor of @xmath149 . applying our results to the core accretion model for the early evolution of jupiter , we find that the planet s growth by gas accretion from a @xmath150 core to its present mass would cause a decrease in the libration amplitude of any trojan companions on small tadpole orbits to @xmath1 of their original size . our representative choice for jupiter s radial migration from @xmath120 to @xmath130 au would result in an increase in the trojans libration amplitudes , eccentricities , and inclinations of only @xmath3 . even for radial migrations of several tens of au , the effects of jupiter s mass growth dominate over the effects of its migration . thus the combined result of mass accretion and radial migration is to stabilize trojan objects by systematically driving them to lower libration amplitudes . also , our numerical integrations show that the libration amplitudes of trojans on larger orbits shrink at an even faster rate . further , the shrinking of horseshoe orbits due to jupiter s growth could place additional objects or perhaps fragments of objects onto stable tadpole orbits . thus , jupiter s growth by mass accretion most likely played a significant role in the capture and evolution of the trojan asteroid population . our results for the evolution of trojan libration amplitudes , eccentricities , and inclinations are quite general and can be applied to other objects within the solar system . for example , eqs . [ analyticresult ] , [ inclaresult ] , and [ eccaresult ] predict that @xmath26 , @xmath151 , and @xmath41 will all decrease substantially if the secondary body undergoes significant outward radial migration . uranus and neptune probably underwent more substantial radial migration due to dynamical friction with planetesimals than jupiter , moving outward by as much as several au ( @xcite , @xcite ) . this would have caused a decrease in @xmath26 , @xmath63 , and @xmath64 of possible trojan - like companions by about @xmath152 . radial migration effects might be even more significant for some planetary satellites , notably our moon . the moon is believed to have formed via a giant collision which produced a temporary ring of debris around the earth ( @xcite and @xcite ) . such a process would have most likely captured some debris in librating orbits about the moon s lagrangian equilibrium points . over the subsequent @xmath153 years , the moon migrated outward to about 30 times its initial orbital radius . ignoring other effects , this migration should have decreased the libration amplitudes , eccentricities , and inclinations of the debris particles to @xmath1 of their original values , stabilizing these objects in 1:1 resonance with the moon . since we observe no such objects today , either the 1:1 resonance was never populated , or other effects ( such as solar gravity ) caused them to be unstable . another potential area for study is the satellite system of saturn . the many resonances in this system are believed to have formed during the significant outward migration of these satellites due to both tidal interactions with saturn and ring torques . one unexplained characteristic of the current saturnian system is that of the six largest satellites near saturn , the middle two , tethys and dione , have a total of three trojan companions but the others , mimas , enceladus , rhea , and titan , have none . this is curious because there is no obvious reason why the middle satellites should be the best at capturing trojan companions . also , the results of this paper suggest that the objects which migrate outward by the greatest amount should be the best at capturing and stabilizing their trojan companions . this suggests that the inner two satellites , which have migrated farthest , should be most likely to have trojan companions . it is likely that the probability of trojan capture and the stabilization of trojan orbits is complicated by the presence of resonances between the satellites . the inner four saturnian satellites are all currently locked in resonances with each other , and they may have passed through various other resonances in the past . an exploration of the interactions between the migration process explored in this paper , and the effects of other resonances , discussed by morais and murray ( 1999 ) , may provide insight into this unexplained characteristic of the saturnian system . it may also provide insight into how the unusual pair of coorbital satellites , janus and epimetheus , which librate on horseshoe orbits , was formed in the saturnian system . our work is also directly relevant to the capture of planetary satellites during the growth of the giant planets , as was suggested by heppenheimer and porco ( 1977 ) . equation [ 2bconstant ] clearly shows that distant satellites would be drawn inward as a planet grows . their migration would cease when the planet reached its final mass . thus , this mechanism provides a natural way for a giant planet to pull in distant satellites without causing them to collide with the planet . press , w. h. , b. p. flannery , s. a. teukolsky , and w. t. vettering 1987 . _ numerical recipes in c : the art of scientific computing _ , cambridge university press , cambridge . analytical prediction with increasing libration amplitude , since the rabe , e. 1954 . the trojans as escaped satellites of jupiter . _ astron . j. _ * 59 * , 433 - 439 . rabe , e. 1972 . orbital characteristics of comets passing through the 1:1 commensurability with jupiter . in _ motion , evolution of orbits , and origin of comets . proceedings , iau symposium no . 45 leningrad _ , ( e.i . chevotarev et al . , springer - verlag , new york / berlin , 55 - 60 . shoemaker , e. m. , c. s. shoemaker , and r. f. wolfe 1989 . trojan asteroids : population , dynamical structure , and origin of the l4 and l5 swarms . in _ asteroids ( r. p. binzel , t. gehrels , and m. s. matthews , eds . ) univ . of arizona press , tucson , 487 - 523 . three sample trojan asteroid orbits are plotted in the frame which corotates with jupiter about the center of mass of the sun - jupiter system . the l4 ( leading ) and l5 ( trailing ) lagrangian equilibrium points are each indicated by the symbol @xmath154 . the orbits shown , which enclose either the l4 or l5 point , but not both , are called tadpoles due to the shape of their librations . the tadpole around the l4 point was integrated with jupiter at twice its present mass , which makes it wider and thus easier to view . the libration amplitude , @xmath155 , is indicated for this orbit . the two tadpoles about the l5 point are the initial ( long , thin tadpole with @xmath156 ) and final ( short , fat tadpole with @xmath157 ) orbits for a trojan as jupiter s mass grows slowly from one - half to twice its current value . the tadpole both shortens and widens as jupiter s mass increases . the trojan libration amplitude , @xmath26 , ( normalized to its initial value , @xmath158 ) is plotted against jupiter s mass , @xmath17 , ( normalized to its initial value , @xmath159 ) on log - log scale for a series of integrations during which jupiter grows from @xmath150 to its current @xmath51 . the initial trojan orbits are small ( @xmath160 ) tadpoles . the analytic prediction of eq . [ analyticresult ] is plotted as a solid line . the numerical curve for the @xmath8 year growth rate ( dotted line ) agrees well with the analytic result . curves for longer growth timescales ( not shown ) agree equally well . the curves for shorter timescales , however , deviate significantly from the analytic curve in a manner which depends on the initial conditions of the orbit . note that the two curves for the @xmath85-year timescale differ only in the initial librational phase of the orbit . the trojan libration amplitude ( normalized to its initial value ) is plotted on a log - log scale for a variety of different - sized initial tadpole orbits as jupiter grows from @xmath150 to its present mass . our analytic result ( eq . [ analyticresult ] ) is plotted as a heavy solid line . the upper dotted curve , which overlays the theoretical curve , is for a tadpole with @xmath161 initially . all smaller tadpoles ( not shown ) agree even better with the analytic prediction . the lower curves in this figure are tadpoles with ( from top to bottom ) @xmath98 , @xmath99 , and @xmath100 initial libration amplitudes . the large tadpole orbits shrink faster than our analytic work predicts . the oscillations in the numerical curves are a result of the analytic approximation used to calculate the libration amplitude and occur at the libration frequency . here we show the behavior of @xmath19 , the longitude of the asteroid in the frame which corotates with jupiter , as jupiter grows from @xmath162 to its present mass in @xmath163 years . jupiter is at @xmath164 , and the initial asteroid orbit is an @xmath165 horseshoe . at @xmath166 years the orbit jumps to an l4 tadpole with @xmath167 . the trojan s libration period is initially about @xmath168 years , and decreases to @xmath169 years when the horseshoe transfers to a tadpole . afterwards , the tadpole s libration period continuously shortens in accordance with eq . [ omega ] . note that the tadpole orbit shrinks most rapidly when its tail ( _ i.e. _ its away - from - jupiter turning point ) is near @xmath170 , since the effective potential is flattest there . further , observe that the lower edge of the plot has a steeper slope for the horseshoe orbit than for the tadpole orbit ; the straight line overlaying the plot is fit by eye to the edge of the horseshoe orbit and has a slope of @xmath103 per jupiter mass doubling . this plot shows the final state of asteroids started on horseshoe orbits at different points during jupiter s growth to its current size of @xmath171 . the vertical axis shows the initial libration amplitude of the horseshoe orbit and the horizontal axis shows the mass of jupiter when the asteroid was placed in that orbit . asteroids which escaped from the 1:1 resonance during the @xmath9 years of the integration are indicated by open circles . objects which remained in horseshoe orbits for the entire integration are shown as filled triangles , and asteroids which were captured into tadpole orbits are shown as stars . most , but not all , of the orbits which became tadpoles remained tadpoles for the rest of the integration . the mixing of final states shown in this figure is an indication of the chaotic nature of the orbits . this plot shows the decrease in the libration amplitudes of those horseshoe orbits from fig . 5 which did not escape the 1:1 resonance plotted against the number of secondary mass doublings . a line with a slope of @xmath107 per doubling was fitted by eye to the data . the low scatter of the points about this line indicates that the decrease in @xmath26 by @xmath107 per doubling is a general property of horseshoe orbits , independent of the mass of the secondary . this plot shows the final libration amplitudes of the asteroids from fig . 5 which were on tadpole orbits at the end of the @xmath9-year integration . the horizontal axis is the mass of jupiter at the time when the asteroids were placed into their initial horseshoe orbits . the orbits represented by points below the long - dashed line are stable for more than @xmath172 years , while those below the short - dashed line are stable for greater than @xmath173 years . these timescales are estimated from the work of levison _ et al . _ ( 1997 ) for tadpoles with zero eccentricity . the square data points show our numerical measurements of the change in the libration amplitude of a trojan asteroid with @xmath174 , @xmath175 , and @xmath176 as jupiter ( on a circular orbit ) grows from @xmath150 to its current mass in @xmath9 years . representative error bars are shown for two data points . the solid line is the analytic prediction for @xmath177 ( eq . [ analyticresult ] ) . the numerical points agree with the analytic curve to within the error bars . this plot shows the eccentricity and inclination of the tadpole orbit whose libration amplitude is plotted in fig . the mean values of the asteroid s eccentricity and inclination are essentially unchanged ( note the vertical scale ) by the growth of jupiter s mass , although the tiny increase in the mean eccentricity is real . the mean eccentricity rises by approximately one small tick mark over @xmath9 years , which is consistent with the @xmath178% increase predicted by eq . [ eccmresult ] . the high frequency oscillations visible in the traces of both @xmath63 and @xmath64 are due to the trojan s librational motion and thus become more rapid as jupiter s mass increases , in accordance with eq . [ omega ] . the low frequency oscillations in the inclination are correlated to the precession of the asteroid s pericenter ( not shown ) driven by the disturbing effects of jupiter . since all the oscillations are caused by jovian perturbations , they increase in amplitude as jupiter s mass grows . these plots compare the orbital evolution of a trojan asteroid a ) without and b ) with jovian mass growth . for both cases , the trojan asteroids start with identical initial conditions and jupiter has an eccentricity of @xmath118 . in a ) , the mass of jupiter is kept constant at @xmath150 , while in b ) jupiter s mass grows from @xmath150 to its current mass in @xmath119 years . both @xmath63 plots show oscillations about a forced eccentricity equal to jupiter s eccentricity . the plots of @xmath64 show the free inclination ( since @xmath179 ) . the low frequency oscillations in @xmath64 are correlated to the oscillations in @xmath63 . the high frequency oscillations visible in the plots of @xmath64 are due to the trojan s librations . the free and forced eccentricities and inclinations of the trojan asteroid are essentially unchanged by jupiter s growth , as predicted in section 2.2 ; however , the frequencies of all the observed oscillations in @xmath63 and @xmath64 increase as jupiter s mass grows . this plot shows the ratio of final to initial libration amplitude for several different - sized tadpole orbits affected by the migration of jupiter from @xmath120 to @xmath130 au over @xmath9 years . jupiter is on a circular orbit . the results of numerical integrations are shown as solid dots with error bars which reflect the difficulties in measuring the libration amplitude . the horizontal line at @xmath180 represents the analytic prediction of eq . [ analyticresult ] which is valid only for small initial libration amplitudes . the numerical results agree well with the analytic prediction for @xmath181 , but deviate increasingly from the prediction for larger initial libration amplitudes . this plot shows the change in the semimajor axis , eccentricity , and inclination of a trojan asteroid on a slightly eccentric and inclined orbit as jupiter ( on a circular orbit ) migrates radially from @xmath182 to @xmath130 au in @xmath9 years . the trojan s eccentricity and inclination increase by a factor of @xmath183 as is predicted by eqs . [ inclaresult ] and [ eccaresult ] . note that the tiny oscillations in @xmath63 and @xmath64 are due primarily to the trojan s librational motion . this plot shows the semimajor axis , eccentricity , and inclination of a trojan asteroid on a slightly eccentric and inclined orbit when jupiter has an eccentricity of @xmath118 and migrates radially from @xmath120 to @xmath141 au in @xmath142 years . the forced components of both the asteroid s eccentricity and inclination remain constant ( @xmath184 and @xmath179 ) ; however , the free components of both @xmath63 and @xmath64 increase like @xmath185 , as predicted by eqs . [ inclaresult ] and [ eccaresult ] .

initially , we approximate the system by the planar circular restricted three - body problem and assume small trojan libration amplitudes . employing an adiabatic invariant calculation , we show that jupiter s thirty - fold growth from a core to its present mass causes the libration amplitudes of trojan asteroids to shrink by a factor of about 2.5 to of their original size . the calculation also shows that jupiter s radial migration has comparatively little effect on the trojans ; inward migration from 6.2 to 5.2 au causes an increase in trojan libration amplitudes of . in each case , the area enclosed by small tadpole orbits , if made dimensionless by using jupiter s semimajor axis , is approximately conserved . similar adiabatic invariant calculations for inclined and eccentric trojans show that jupiter s mass growth leaves the asteroid s eccentricities and inclinations essentially unchanged , while one au of inward migration causes an increase in both of these quantities by . we demonstrate that our predictions remain valid for trojans with small libration amplitudes even when the asteroids have low , but nonzero , eccentricities and inclinations and/or jupiter has an eccentricity similar to its present value . the integrations also show that trojans with large libration amplitudes , including horseshoe orbits , are even more strongly affected by jupiter s mass growth and radial migration than simple scaling from our analytic results would suggest . thus , if jupiter captured most of its trojan companions before or while it accreted gas , as seems probable , then jupiter s growth played a significant role in stabilizing trojan objects by systematically driving them to lower libration amplitudes .

we present analytic and numerical results which illustrate the effects of jupiter s accretion of nebular gas and the planet s radial migration on its trojan companions . initially , we approximate the system by the planar circular restricted three - body problem and assume small trojan libration amplitudes . employing an adiabatic invariant calculation , we show that jupiter s thirty - fold growth from a core to its present mass causes the libration amplitudes of trojan asteroids to shrink by a factor of about 2.5 to of their original size . the calculation also shows that jupiter s radial migration has comparatively little effect on the trojans ; inward migration from 6.2 to 5.2 au causes an increase in trojan libration amplitudes of . in each case , the area enclosed by small tadpole orbits , if made dimensionless by using jupiter s semimajor axis , is approximately conserved . similar adiabatic invariant calculations for inclined and eccentric trojans show that jupiter s mass growth leaves the asteroid s eccentricities and inclinations essentially unchanged , while one au of inward migration causes an increase in both of these quantities by . numerical integrations confirm and extend these analytic results . we demonstrate that our predictions remain valid for trojans with small libration amplitudes even when the asteroids have low , but nonzero , eccentricities and inclinations and/or jupiter has an eccentricity similar to its present value . the integrations also show that trojans with large libration amplitudes , including horseshoe orbits , are even more strongly affected by jupiter s mass growth and radial migration than simple scaling from our analytic results would suggest . further , the numerical runs demonstrate that jupiter s predicted mass growth is sufficient to cause the capture of asteroids initially on horseshoe orbits into stable tadpole orbits . thus , if jupiter captured most of its trojan companions before or while it accreted gas , as seems probable , then jupiter s growth played a significant role in stabilizing trojan objects by systematically driving them to lower libration amplitudes . key words : + asteroids , dynamics + celestial mechanics + jupiter + origin , solar system + resonances + astronomy department , university of maryland + heather j. fleming + astronomy department + university of maryland + college park , md 20742 - 2421 + tel : ( 301 ) 474 - 7582 + fax : ( 301 ) 314 - 9067 + e - mail : hcohen@astro.umd.edu + douglas p. hamilton + astronomy department + university of maryland + college park , md 20742 - 2421 + tel : ( 301 ) 405 - 1548 + fax : ( 301 ) 314 - 9067 + e - mail : hamilton@astro.umd.edu + submitted to _ icarus _ : june 16 , 1999 + revised : + 41 pages + 13 figures and 2 tables + running head : origin of the trojan asteroids + corresponding author : + douglas p. hamilton + astronomy department + university of maryland + college park , md 20742 - 2421 + tel : ( 301 ) 405 - 1548 + fax : ( 301)314 - 9067 + e - mail : hamilton@astro.umd.edu +

astro-ph0305279

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the sun s magnetic activity is expected to have greatly decreased with time ( skumanich 1972 ; simon , boesgaard , & herbig 1985 ; dorren & guinan 1994 ; guinan , ribas , & harper 2002 ) as the solar rotation slows down because of angular momentum loss in the stellar wind and resultant reduction in magnetic dynamo - related activity . the study of the young sun s far - ultraviolet ( fuv ) fluxes using solar proxies provides important diagnostics for the state of the younger solar system and the physics of the much more active early sun . the comprehensive `` sun in time '' project , begun in 1988 ( dorren & guinan 1994 ) , focuses on the study of the long - term evolution of the outer atmosphere of an early g star , from the zero - age main sequence to the terminal - age main sequence . a crucial component of the program is a carefully - selected sample of nearby solar analogs ( gdel , guinan , & skinner 1997 ) with spectral types confined between g0 - 5 v and with well - determined physical properties ( including temperatures , luminosities , and metal abundances ) . we have obtained extensive photometry ( @xmath8 ) of these stars from ground - based observatories for over a decade to determine their rotation periods , investigate starspots and possible activity cycles . in addition , we have been able to estimate the stellar ages by making use of their memberships in clusters and moving groups , rotation period age relationships , and , for the older stars , fits to stellar evolution models . the sample of solar proxies within the `` sun in time '' program ( see guinan , ribas & harper 2002 ) contains stars that have masses close to 1 m@xmath9 and cover most of the sun s main sequence lifetime from @xmath0130 myr to @xmath09 gyr . basically , the program stars have similar convective - zone depths and chemical abundances to those of the sun and vary only by their age and rotation periods ( @xmath10 ) , and hence dynamo - generated magnetic activity , i.e. , chromospheric , transition region ( tr ) , and coronal emissions . in essence , we use these one solar mass stars with @xmath10 between 2.7 and @xmath035 days as laboratories to study and test solar and stellar dynamo theories by varying essentially only one parameter : rotation period . the `` sun in time '' is a comprehensive and multi - frequency program that addresses a variety of topics : study of short- and long - term magnetic evolution ; physics and energy transfer mechanisms of the chromosphere , transition region ( tr ) and corona ; evolution of the spectral irradiances of the sun and their effects on paleo - planetary environments and atmospheres . to this end we utilize observational data spanning almost the entire electromagnetic spectrum , which allows us to probe the structure of stellar / solar atmospheres . the fuv has not been readily accessible until the successful launch of the _ far ultraviolet spectroscopic explorer _ ( fuse ) . fuse allows a critical probe of the hot plasmas over nearly three decades in temperature : e.g. , @xmath1 k for the h i lyman series ( ly@xmath11 , ly@xmath12 , ... ) through o vi @xmath131032 , 1038 at @xmath14 k , and the recently identified fe xviii @xmath3975 coronal emission feature at @xmath2 k. several of the strongest emission features , such as c iii @xmath13977,1176 and o vi @xmath131032,1038 , originate in tr plasmas , and are pivotal for understanding the mechanisms of chromospheric and coronal heating . thus , spectrophotometry with fuse fills the energy gap between iue / hst ( 11603200 ) and euve ( 80720 ) to yield a complete and comprehensive picture of a solar - type star s atmosphere at different ages and rotation periods . in this paper we present and analyze fuse observations of six bright solar analogs that span a wide range of rotation periods ( and ages ) from 2.7 days ( @xmath0130 myr ) to @xmath035 days ( @xmath09 gyr ) . the stars , whose properties are listed in table [ tabprop ] along with the sun s , are : ek dra , @xmath15 uma , @xmath16 cet , @xmath11 com , @xmath11 hyi , and 16 cyg a. the present study focuses on two particular aspects of the `` sun in time '' program that can be effectively addressed with fuv observations : _ 1 . ) _ the flux ratios between the c iii @xmath31176 and c iii @xmath3977 lines ( both within the fuse spectral range ) yield empirical measures and estimates of the electron pressure ( @xmath17 ) of the tr ; _ 2 . ) _ integrated fluxes for selected emission lines can be used to study the evolution of the solar fuv irradiances at different ages and rotation periods .

the emission features in the fuse 9201180 wavelength range allow for a critical probe of the hot plasma over three decades in temperature : k for the h i lyman series to k for the coronal fe xviii line . using the flux ratio c iii/ as diagnostics , we investigate the dependence of the electron pressure of the transition region as a function of the rotation period , age and magnetic activity . the observations indicate that the average surface fluxes of the analyzed emission features strongly decrease with increasing stellar age and longer rotation period .

we present and analyze _ far ultraviolet spectroscopic explorer _ ( fuse ) observations of six solar analogs . these are single , main - sequence g05 stars selected as proxies for the sun at several stages of its main - sequence lifetime from myr up to gyr . the emission features in the fuse 9201180 wavelength range allow for a critical probe of the hot plasma over three decades in temperature : k for the h i lyman series to k for the coronal fe xviii line . using the flux ratio c iii/ as diagnostics , we investigate the dependence of the electron pressure of the transition region as a function of the rotation period , age and magnetic activity . the results from these solar proxies indicate that the electron pressure of the stellar-k plasma decreases by a factor of between the young , fast - rotating ( d ) magnetically active star and the old , slow - rotating ( d ) inactive star . also , we study the variations in the total surface flux for specific emission features that trace the hot gas in the stellar chromosphere ( c ii ) , transition region ( c iii , o vi ) , and corona ( fe xviii ) . the observations indicate that the average surface fluxes of the analyzed emission features strongly decrease with increasing stellar age and longer rotation period . the emission flux evolution with age or rotation period is well fitted by power laws , which become steeper from cooler chromospheric ( k ) to hotter coronal ( k ) plasma . the relationship for the integrated ( 9201180 ) fuse flux indicates that the solar far - ultraviolet ( fuv ) emissions were about twice the present value 2.5 gyr ago and about 4 times the present value 3.5 gyr ago . note also that the fuse / fuv flux of the zero - age main sequence sun could have been higher by as much as 50 times . our analysis suggests that the strong fuv emissions of the young sun may have played a crucial role in the developing planetary system , in particular through the photoionization , photochemical evolution and possible erosion of the planetary atmospheres . some examples of the effects of the early sun s enhanced fuv irradiance on the atmospheres of earth and mars are also discussed .

astro-ph0305279

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in this study we have utilized fuv spectra acquired with the fuse satellite to investigate the fuv emission characteristics of solar analogs . our six targets are well - known g05 solar - type stars especially selected to serve as proxies for the sun at different ages , nearly covering the entire solar main sequence lifetime from 130 myr to @xmath09 gyr . here we have focused on two aspects of the `` sun in time '' program which are the study of tr plasma electron pressures ( using c iii @xmath31176/@xmath3977 line ratio diagnostics ) for stars that differ only in rotation period ( and age ) and the evolution of irradiances for specific features covering emitting plasma with temperatures from @xmath1 k to @xmath7 k. to analyze the plasma density of the tr we have used a theoretical relationship between the ratio of c iii @xmath31176 and @xmath3977 emission line fluxes and the electron pressure ( @xmath17 ) of the material responsible for the emission . fortunately , both c iii transitions are within the fuse wavelength range so that they can be measured simultaneously . our results indicate a power - law relationship between the electron pressure and the stellar rotation period and overall magnetic - related activity ( both related to age ) . the slope of this relationship has been found to be @xmath0@xmath821.7 , which suggests that the electron pressure of @xmath010@xmath4-k material in the sun has decreased significantly since the beginning of its main sequence evolution . the higher values of electron pressure found for the more active stars are best explained by stronger magnetic confinment of the tr plasma . the measured fluxes for four emission features c ii @xmath31037 , c iii @xmath3977 , o vi @xmath31032 , and fe xviii @xmath3975 were referred to a radius of 1 @xmath83 and also corrected for ism absorption whenever necessary . the typical formation temperatures of the studied features are @xmath37 k , @xmath38 k , @xmath39 k , and 6 mk , respectively . our analysis indicates that the evolution of these fluxes with stellar rotation period or age can be accurately fit with power - law relationships of different slopes . interestingly , the slopes not only change from line to line , but also they show a clear trend : the power law becomes steeper as we move from cooler to hotter plasmas , with the most extreme trend being that of the coronal ion fe xviii . also , the evolution total integrated flux in the fuse wavelength range ( 9201180 ) can be fit with a power - law relationship with a slope of @xmath0@xmath821.7 , which indicates a factor of @xmath050 flux decrease along the solar main sequence evolution as the magnetic dynamo activity decreases . the high levels of fuv line emission fluxes ( and related high - energy emission ) of the early sun could have played a crucial role in the photochemistry and photoionization of terrestrial and planetary atmospheres . to address this point we are completing spectral irradiance tables covering 1 to 3200 for our program stars that can serve as input data for evolution and structure models of the paleo - atmospheres of the solar system planets . the fuse observations fill a critical wavelength and energy gap in the `` sun in time '' program and complement observations of the same stars in the x - ray and euv regions ( corona ) made with rosat , sax , asca , xmm , chandra , and euve , and in the uv ( tr and chromosphere ) made using iue and hst . the only missing piece of information is the evolution of the irradiance of the strong chromospheric h i ly@xmath35 @xmath31216 fuv feature . we are currently carrying out this part of the study and we expect to complete it shortly . full spectral irradiance tables for five solar proxies are thus nearing completion and will be made available in a forthcoming publication ( ribas & guinan 2003 , in preparation ) . we anticipate that these irradiance results will be important for the study of paleo - atmospheres of the solar system planets . in particular , preliminary analyses indicate that the high x - ray and euv emission fluxes of the early sun could have produced significant heating of the planetary exospheres and upper - atmospheres thus enhancing processes such as thermal escape . the early sun s strong fuv and uv fluxes penetrate further into the atmosphere and probably influenced the photochemistry of , e.g. , methane and ammonia , which are important greenhouse gases . thus , this study has strong implications for the evolution of the pre - biotic and archean atmosphere of the earth as well as for the early development of life on earth and possibly on mars . we thank seth redfield for making available to us the data from the colorado lism model , which we have used to correct the measured fluxes for ism absorption . the referee , tom ake ( johns hopkins univ . ) , is thanked for helpful comments and suggestions that led to significant improvements . we acknowledge with gratitude the support for the `` sun in time '' program from nasa - fuse grants nag 5 - 08985 , nag 5 - 10387 , nag 5 - 12125 and also from nsf - rui grant ast-00 - 71260 . g.m.h.s research was funded by nasa grant nag5 - 4808 ( ltsa ) . this research has made use of the simbad database , operated at cds , strasbourg , france . ake , t. b. , dupree , a. k. , young , p. r. , linsky , j. l. , malina , r. f. , griffiths , n. w. , siegmund , o. h. w. , & woodgate , b. e. 2000 , , 538 , l87 allard , n. , artru , m .- c . , lanz , t. , & le dourneuf , m. 1990 , , 84 , 563 arnaud , m. , & rothenflug , r. 1985 , , 60 , 425 ayres , t. r. 1997 , jgr , 102 , 1641 berrington , k. a. 1985 , j. phys . phys . , 18 , l395 berrington , k. a. , burke , p. g. , dufton , p. l. , & kingston , a. e. 1985 , atomic nucl . data tables , 33 , 195 bhatia , a. k. , & kastner , s. o. 1992 , , 79 , 139 canuto , v. m. , levine , j. s. , augustsson , t. r. , & imhoff , c. l. 1982 , nature , 296 , 816 canuto , v. m. , levine , j. s. , augustsson , t. r. , imhoff , c. l. , & giampapa , m. s. 1983 , nature , 305 , 281 dorren , j. d. , & guinan , e. f. 1994 , in iau coll . 143 , the sun as a variable star , eds . j. m. pap , c. frlich , h. s. hudson , & s. k. solanki ( cambridge : cup ) , 206 doyle , j. g. , kingston , a. e. , & reid , r. h. g. 1980 , , 90 , 97 doyle , j. g. , raymond , j. c. , noyes , r. w. , & kingston , a. e. 1985 , , 297 , 816 dupree , a. k. , foukal , p. v. , & jordan , c. 1976 , , 209 , 621 feldman , u. , & doschek , g. a. 1991 , , 75 , 925 fleming , j. , hibbert , a. , & stafford , r. p. 1984 , physica scripta , 49 , 316 gayley , k. g. 2002 , , 565 , 545 grevesse , n. , & sauval , a. j. 1998 , space science reviews , 85 , 161 gdel , m. , guinan , e. f. , & skinner , s. l. 1997 , , 483 , 947 guinan , e. f. , ribas , i. , & harper , g. m. 2002 , in asp conf . 264 , continuing the challenge of euv astronomy : current analysis and prospects for the future , eds . s. b. howell , j. dupuis , d. golombek , f. m. walter , & j. cullison ( san francisco : asp ) , 129 heroux , l. , & hinteregger , h. e. 1978 , jgr , 83 , 5305 jordan , c. 2000 , plasma phys . control fusion , 42 , 415 jordan , c. , ayres , t. r. , brown , a. , linsky , j. l. , & simon , t. 1987 , , 225 , 903 judge , p. g. , woods , t. n. , brekke , p. , & rottman , g. j. 1995 , , 455 , l85 keenan , f. p. , & berrington , k. a. 1985 , solar phys . , 99 , 25 lammer , h. , lichtenegger , h. , kolb , c. , ribas , i. , guinan , e. f. , & bauer , s. j. 2003 , icarus , in press linsky , j. l. , & wood , b. e. 1994 , , 430 , 342 luhmann , j. g. , & bauer , s. j. 1992 , in venus and mars : atmospheres , ionospheres , and solar wind interactions , proceedings of the chapman conference ( washington , dc : american geophysical union ) , 417 macpherson , k. p. , & jordan , c. 1999 , , 308 , 510 montesinos , b. , & jordan , c. 1993 , , 264 , 900 moore , c. e. 1970 , nsrds - nbs 3 nbs , washington , d.c . moos , h. w. , cash , w. c. , cowie , l. l. , et al . 2000 , , 538 , l1 nussbaumer , h. & storey , p. j. 1978 , , 64 , 139 noyes , r. w. , raymond , j. c. , doyle , j. g. , & kingston , a. e. 1985 , , 297 , 805 oranje , b. j. 1986 , , 154 , 185 pavlov , a. a. , kasting , j. f. , brown , l. l. , rages , k. a. , & freedman , r. 2000 , jgr , 105 , 11981 redfield , s. , & linsky , j. l. 2000 , , 534 , 825 redfield , s. , & linsky , j. l. 2002 , , 139 , 439 redfield , s. , ayres , t. r. , linsky , j. l. , ake , t. b. , dupree , a. k. , robinson , r. d. , & young , p. r. 2003 , , 585 , 993 redfield , s. , linsky , j. l. , ake , t. b. , ayres , t. r. , dupree , a. k. , robinson , r. d. , wood , b. e. , & young , p. r. 2002 , , 581 , 626 ryans , r. s. i. , foster - woods , v. j. , reid , r. h. g. , keenan , f. p. , & copeland , f. 1990 , , 336 , 393 rye , r. , kuo , p. h. , & holland , h. d. 1995 , nature , 378 , 603 sagan , c. , & mullen , g. 1972 , science , 177 , 52 sagan , c. , & chyba , c. 1997 , science , 276 , 1217 sahnow , d. j. , moos , h. w. , ake , t. b. , et al . 2000 , , 538 , l7 shorer , p. , & lin , c. d. 1977 , phys . a. , 16 , 2068 simon , t. , boesgaard , a. m. , & herbig , g. 1985 , , 293 , 551 skumanich , a. 1972 , , 171 , 565 spitzer , l. 1978 , physical processes in the interstellar medium ( new york : john wiley ) tachiev , g. , & froese fischer , c. 1999 , j. phys . b. , 32 , 5805 wood , b. e. , linsky , j. l. , & ayres , t. r. 1997 , , 478 , 745 wood , b. e. , mller , h .- r . , zank , g. , & linsky , j. l. 2002a , , 574 , 412 wood , b. e. , redfield , s. , linsky , j. l. , & sahu , m. s. 2002b , , 581 , 1168 young , p. r. , dupree , a. k. , wood , b. e. , redfield , s. , linsky , j. l. , ake , t. b. , & moos , h. w. 2001 , , 555 , l121 zhang , h. l. , sampson , d. h. , & fontes , c. j. 1990 , atomic data nucl . data tables , 44 , 31 lrlrcccccl ek dra & 129333 & g0 v & 33.9 & 5818&1.07&0.95&2.75 & 0.13 & pleiades str . + @xmath15 uma & 72905 & g1.5 v&14.3 & 5840&0.98&0.97&4.68 & 0.3 & uma str . + @xmath16 cet & 20630 & g5 v & 9.2 & 5700&1.01&0.94&9.2 & 0.65 & @xmath10-age rel . + @xmath11 com & 114710 & g0 v & 9.2 & 5950&1.11&1.08&12.4 & 1.6 & @xmath10-age rel . + sun & & g2 v & 1 au&5777&1.00&1.00&25.4 & 4.6 & isotopic dating + @xmath11 hyi & 2151 & g2 iv & 7.5 & 5800&1.09&1.88&@xmath028&6.7 & isochrones + 16 cyg a & 186408 & g2 v & 21.6 & 5740&0.99&1.27&@xmath035&@xmath09 & isochrones + lclccrrrrr ek dra & c1020501 & 2002 may 14 & 24.2&11.1@xmath840.7 & 7.6@xmath840.4 & 7.3@xmath840.3 & 3.4@xmath840.2 & 0.47@xmath840.07 & 0.81@xmath840.19 + @xmath15 uma & b0780101 & 2001 dec 5 & 16.5&14.7@xmath840.7 & 9.3@xmath840.5 & 9.6@xmath840.3 & 4.8@xmath840.2 & 0.74@xmath840.09 & 0.65@xmath840.26 + @xmath16 cet & a0830301 & 2000 sep 10 & 13.0&16.4@xmath840.7 & 10.7@xmath840.4 & 12.4@xmath840.4 & 6.2@xmath840.2 & 1.07@xmath840.12 & 0.44@xmath840.14 + @xmath11 com & a0830401 & 2001 jan 26 & 15.0&11.0@xmath840.5 & 5.5@xmath840.2 & 5.9@xmath840.2 & 2.8@xmath840.1 & 0.63@xmath840.08&@xmath850.06 + @xmath11 hyi & a0830101 & 2000 jul 1 & 18.0&15.1@xmath840.5 & 5.8@xmath840.2 & 6.1@xmath840.2 & 2.8@xmath840.1 & 1.02@xmath840.09&@xmath850.04 + 16 cyg a & c1020101 & 2002 jul 30 & 35.0&0.66@xmath840.14&0.20@xmath840.09&0.43@xmath840.05&0.20@xmath840.03&@xmath850.05&@xmath850.04 + lrrrrrrrrr ek dra & @xmath8230.5&@xmath8223 & 8 & @xmath8215 & 16 & @xmath8225 & 6 & @xmath8226 & 5 + @xmath15 uma & @xmath8212.0&@xmath8223 & @xmath8211 & @xmath8224 & @xmath8212 & @xmath8219 & @xmath827 & @xmath8251 & @xmath8239 + @xmath16 cet & 19.9 & 12 & @xmath828 & 16 & @xmath824 & 16 & @xmath824 & 1 & @xmath8219 + @xmath11 com & 6.1 & 3 & @xmath823 & 0 & @xmath826 & 4 & @xmath822 & & + @xmath11 hyi & 22.7 & 6 & @xmath8217 & 20 & @xmath823 & 16 & @xmath827 & & + 16 cyg a & @xmath8225.6&@xmath8240&@xmath8214 & @xmath8229 & @xmath823 & @xmath8222 & 4 & & + lllllr ek dra & 1.17@xmath840.18 & 28.4@xmath841.7 & 18.2@xmath840.8 & 2.02@xmath840.51 & + @xmath15 uma & 0.32@xmath840.04 & 6.52@xmath840.33 & 4.10@xmath840.12 & 0.28@xmath840.11 & 45@xmath8420 + @xmath16 cet&0.20@xmath840.02 & 3.30@xmath840.15 & 2.32@xmath840.07 & 0.082@xmath840.025&16.4@xmath843.8 + @xmath11 com & 0.090@xmath840.011&1.64@xmath840.07 & 0.842@xmath840.030&@xmath850.0085 & + @xmath11 hyi & 0.032@xmath840.003&0.543@xmath840.019&0.190@xmath840.007&@xmath850.0012 & + 16 cyg a & @xmath850.03 & 0.423@xmath840.090&0.246@xmath840.028&@xmath850.02 & + lcll fuv ( 9201180 ) & @xmath86&@xmath821.74&@xmath821.03 + c ii & @xmath87 & @xmath821.49&@xmath820.88 + c iii & @xmath88 & @xmath821.61&@xmath820.95 + o vi & @xmath89 & @xmath821.82&@xmath821.07 + x - rays ( 0.12.4 kev)&@xmath90 & @xmath822.64&@xmath91 + fe xviii & @xmath92 & @xmath823.2 & @xmath821.9 + lccl ek dra & 0.68@xmath840.05&0.67@xmath840.05&@xmath9316.0 + @xmath15 uma & 0.63@xmath840.05&0.61@xmath840.04&@xmath94 + @xmath16 cet&0.65@xmath840.04&0.60@xmath840.04&@xmath95 + @xmath11 com & 0.50@xmath840.03&0.48@xmath840.03&@xmath96 + @xmath11 hyi & 0.38@xmath840.02&0.33@xmath840.02&@xmath97 + 16 cyg a & 0.30@xmath840.15&0.27@xmath840.13&@xmath98 +

we present and analyze _ far ultraviolet spectroscopic explorer _ ( fuse ) observations of six solar analogs . these are single , main - sequence g05 stars selected as proxies for the sun at several stages of its main - sequence lifetime from myr up to gyr . the emission flux evolution with age or rotation period is well fitted by power laws , which become steeper from cooler chromospheric ( k ) to hotter coronal ( k ) plasma .

we present and analyze _ far ultraviolet spectroscopic explorer _ ( fuse ) observations of six solar analogs . these are single , main - sequence g05 stars selected as proxies for the sun at several stages of its main - sequence lifetime from myr up to gyr . the emission features in the fuse 9201180 wavelength range allow for a critical probe of the hot plasma over three decades in temperature : k for the h i lyman series to k for the coronal fe xviii line . using the flux ratio c iii/ as diagnostics , we investigate the dependence of the electron pressure of the transition region as a function of the rotation period , age and magnetic activity . the results from these solar proxies indicate that the electron pressure of the stellar-k plasma decreases by a factor of between the young , fast - rotating ( d ) magnetically active star and the old , slow - rotating ( d ) inactive star . also , we study the variations in the total surface flux for specific emission features that trace the hot gas in the stellar chromosphere ( c ii ) , transition region ( c iii , o vi ) , and corona ( fe xviii ) . the observations indicate that the average surface fluxes of the analyzed emission features strongly decrease with increasing stellar age and longer rotation period . the emission flux evolution with age or rotation period is well fitted by power laws , which become steeper from cooler chromospheric ( k ) to hotter coronal ( k ) plasma . the relationship for the integrated ( 9201180 ) fuse flux indicates that the solar far - ultraviolet ( fuv ) emissions were about twice the present value 2.5 gyr ago and about 4 times the present value 3.5 gyr ago . note also that the fuse / fuv flux of the zero - age main sequence sun could have been higher by as much as 50 times . our analysis suggests that the strong fuv emissions of the young sun may have played a crucial role in the developing planetary system , in particular through the photoionization , photochemical evolution and possible erosion of the planetary atmospheres . some examples of the effects of the early sun s enhanced fuv irradiance on the atmospheres of earth and mars are also discussed .

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various mechanisms have been proposed as sources of excitation in the nebulae , including photoionisation by radiation from the agn , cluster x - rays , or hot stars , collisional heating by high - energy particles , shocks or cloud - cloud collisions , and conduction of heat from the x - ray corona ( peterson et al . . however , none so far satisfactorily describes all the characteristic spectra , energetics , and kinematics of the extended emission - line regions ( wilman et al . 2006 ; hatch et al . 2007 ) . we reiterate that the fov of the observations are only 3.5 @xmath25 5 arcsec ( corresponding to the central few parsec see table [ table : objects ] ) . these results only look at the very heart of these sources . therefore , it is really only the emission mechanisms for the gas at the very center of these systems that is being studied here . the forbidden lines such as [ nii]@xmath16583 result from the excitation of n@xmath37 through collisions with electrons liberated through photoionisation . the h@xmath0 emission results from the recombination of the hydrogen ion . [ nii]@xmath16583 flux depends on the n@xmath37 abundance , the strength of the radiation field , and the form of the radiation field : a harder ionising source will produce a greater flux . the h@xmath0 flux also depends on the strength of the radiation field . therefore , the ratio will depend on the metallicity of the gas and the form of the ionising radiation . the form of the ionising radiation and/or the gas metallicity are not uniform but must vary within each galaxy and between the whole sample . different excitation mechanisms may act in different regions ( hatch et al . 2007 , edwards et al . 2009 ) , or the h@xmath0 emission might be disturbed by the presence of companion galaxies ( wilman et al . 2006 ) . a commonly used method to distinguish between the sources of ionisation uses the emission - line diagrams pioneered by baldwin , phillips @xmath4 terlevich ( 1981 , hereafter bpt diagram ) which separate the two major origins of emission : star formation and agn . the diagrams use pairs of emission line ratios , of which the most commonly used is [ oiii]@xmath15007/h@xmath2 against [ nii]@xmath16584/h@xmath0 . extinction - corrected emission - line measurements were used ( even though the bpt diagram is almost insensitive to reddening ) . we plot the bpt diagrams in figures [ fig : mcg_bpt ] and [ fig : ugc_bpt ] using the following criteria : kewley criteria : galaxies above this line are agn . kewley et al . ( 2001 ) used a combination of photoionisation and stellar population synthesis models to place a theoretical upper limit on the location of star forming galaxies on the bpt diagram , @xmath38}{h\beta } = 0.61/{\log([nii]/h\alpha)-0.47}+1.19)$ ] . kauffmann et al . ( 2003 ) criteria : galaxies below this line are purely star forming . between kewley and kauffmann criteria is composite objects . kauffmann et al . ( 2003 ) revised the criteria as follows : a galaxy is defined to be an agn if @xmath38}{h\beta } > 0.61/{\log([nii]/h\alpha)-0.05}+1.3)$ ] . liners seyffert line ( schawinsky et al . 2007 ) : this line distinguishes liners from seyffert galaxies @xmath38}{h\beta } ) = 1.05 \log(\frac{[nii]}{h\alpha})+0.45 $ ] . sdss emission - line galaxies occupy a well - defined region shaped like the wings of a seagull ( stasinska et al . although the exact location of the line dividing the star forming and active galactic nuclei galaxies is still controversial ( kewley et al 2001 ; kauffmann et al 2003 ; stasinska et al 2006 ) . all galaxies show important liner emission , but that at least one has significant seyfert emission areas , and at least one other has significant hii like emission line ratios for many pixels as shown in figures [ fig : mcg_bpt ] and [ fig : ugc_bpt ] . this is in agreement with the long - slit data of these sources plotted on bpt diagrams in figure 3 of mcdonald et al . ( 2012 ) . however , there is a debate about the ionisation mechanism in liners ( low - ionisation nuclear emission - line region ) . the most viable excitation mechanisms are : a low accretion - rate agn ( kewley et al . 2006 ) , photoionisation by old post - asymptotic giant branch ( pagb ) stars ( stasinska et al . 2008 ) , and fast shocks ( dopita @xmath4 sutherland 1995 ) . sarzi et al . ( 2010 ) investigate the ionising sources for the gas in elliptical galaxies based on sauron intergral - field spectroscopy whose spectra are limited to a relatively narrow wavelength range . they conclude that pagb stars are the main source of ionisation . in contrast , annibali et al . ( 2010 ) analyse long - slit spectra of 65 ellipticals and claim that their nuclear line emission can be explained by excitation from the hard ionising continuum from an agn and/or fast shocks . however , they can not completely rule out a contribution from pagb stars at large radii . voit @xmath4 donahue ( 1997 ) suggested that sources of supplementary heating produce the liner - like properties of the spectra , though not necessarily through the same mechanism in all systems . annibali et al . ( 2010 ) found that from the centre outward , galaxies move left and down in the bpt diagram for their study of 65 early - type galaxies . thus , the hardness of the ionising continuum decreases with galactocentric distance ( up to half the half - light radius in the annibali et al . ( 2010 ) sample ) . figures [ fig : mcg_bpt ] and [ fig : ugc_bpt ] also show the flux ratios as function of distance from the galaxy centre . the red circles indicate the central 0.5 @xmath25 0.5 arcsec of the galaxy , the yellow circles 1.0 @xmath25 1.0 arcsec , and the blue circles the full 3.5 @xmath25 5.0 arcsec . the centre of the galaxy was determined as the luminosity peak in the continuum images in figure [ fig : thumbnails ] . in our case , the hardness of the ionising continuum stay mostly uniform with galactocentric distance over out limited spatial extend . pgc044257 show an interesting core separation of the emission in the very centre of the galaxy in figure [ fig : ugc_bpt]a . there is also the debate about which galaxies are liners ( agn ) and which have just liner - like emission ( non - agn ) . the division is usually made by looking at the extend of the liner signature : core dominated mean true liner and diffuse means liner - like . the arising problem is that the scale of the sdss fibers is already too large to make the distinction for most galaxies . for the nearby galaxies , the centroiding of the fibres is not accurate enough to be sure if the measured spectra cover the core of the galaxy . we have core dominated liner emission for at least three out of the four galaxies . additional confirmation comes from the fact that at least one of our galaxies ( pgc026269 ) is a strong radio source ( agn , see [ table : objects2 ] ) . similarly , our findings for ugc09799 agree with edwards et al . ( 2009 ) who found line ratios consistent with seyffert or liner activity in most of their central spaxels for ugc09799 . edwards ( 2009 ) also found that the seyffert signature dominated the central spaxels of the ccg ( ugc09799 ) . the h@xmath0 emission surrounding the bcg in this cluster is coincident with radio - blown bubbles in the central region of the cluster . these bubbles to the north and south of the cluster core are filled with radio emission , which likely originated from the agn within the ccg ( blanton et al . 2003 ) . since the h@xmath0 emission seen by mcdonald et al . ( 2010 ) is primarily along the edges of the northern bubble , they suspect that shocks may be responsible for the heating in this case . however , for pgc044257 , mcdonald et al . ( 2010 ) find very little evidence for an agn in the cluster hosting the galaxy , in terms of the radio power , x - ray morphology and hard x - ray flux . two of the galaxies in the current study have detected x - ray point sources in the ccg ( pgc026269 and ugc09799 ) with large cavities in their x - ray haloes , suggesting that the agn is influencing the surrounding medium . we investigate this further by plotting the other bpt diagrams , on a spaxel - by - spaxel basis , for all four galaxies ( shown in figure [ fig : bpts ] ) : [ oiii]@xmath15007/h@xmath2 vs [ nii]@xmath16584/h@xmath0 , [ oiii]@xmath15007/h@xmath2 vs [ sii]@xmath36717,6731/h@xmath0 , and [ oiii]@xmath15007/h@xmath2 vs [ oi]@xmath16300/h@xmath0 . one bcg pgc026269 show several hii pixels in all three bpt diagrams . figure [ fig : mcg_bpt ] show that these hii pixels occur throughout the centre of the galaxy . on these plots , we compare our observations to the photoionisation models for pagb stars with z = z@xmath14 ( binette et al . these models are consistent with most of our observations . a model with z=1/3 z@xmath14 will be shifted towards lower values on the x - axis of the three bpts . the pagb scenario has recently been revisited by stasnska et al . ( 2008 ) , whose extensive grid of photoionisation models ( see their figure 5 ) cover most of the regions occupied by our spatially resolved measurements . three other grids of ionisation models are overplotted on the bpt diagrams ( figure [ fig : bpts ] ) . the plotted agn photoionisation models ( groves , dopita @xmath4 sutherland 2004 ) have an electron density , n@xmath39 = 100 @xmath16 , metallicities of solar , z = z@xmath14 ( red grids ) , and twice solar ( green grids ) , a range of ionisation parameter ( 3.6 @xmath40 0.0 ) and a power - law ionising spectrum with spectral index @xmath0 = 2 , 1.4 , and 1.2 . a harder ionising continuum , with @xmath0 = 1.2 , boosts [ sii]@xmath416717,6731 and [ oi]@xmath16300 relative to h@xmath0 . we also compared our results with shock models ( allen et al . 2008 , purple grids ) . in figure [ fig : bpts ] , we plot the grids with z = z@xmath14 , preshock densities of 100 @xmath16 , shock velocities of 100 , 500 and 1000 km s@xmath11 , and preshock magnetic fields of b=1 , 5 and 10 @xmath42 g . shock models with a range of magnetic field strengths ( b=1,5 and 10 @xmath42 g ) match our observations . interstellar magnetic fields of b @xmath31 1 10 @xmath42 g are typical of what is observed in elliptical galaxies ( mathews @xmath4 brighenti 1997 ) . overall , shock models reproduce the majority of our data in the three emission - line ratio diagrams . the shock grids with lower metallicity ( e.g. lmc and smc metallicities ) are not consistent with our measurements.brent/itera.html . ] as shown in table [ table : objects2 ] we have very weak as well as strong radio fluxes in our small sample . we therefore believe that we are not particularly prone to biases such as the fact that a priori choice of galaxies with strong radio fluxes will result in finding a sample where high [ nii]/h@xmath0 would be more common than in an optically , or h@xmath0 selected sample only where starforming high h@xmath0/[nii ] sources might be more abundant .

based on optical diagnostic ratios ( [ oiii]/h against [ nii]/h , [ sii],6731/h , and [ oi]/h ) , all galaxies show extended liner emission , but that at least one has significant seyfert emission areas , and at least one other has significant hii like emission line ratios for many pixels .

we present detailed integral field unit ( ifu ) observations of the central few kiloparsecs of the ionised nebulae surrounding four active central cluster galaxies ( ccgs ) in cooling flow clusters ( abell 0496 , 0780 , 1644 and 2052 ) . our sample consists of ccgs with h filaments , and have existing data from the x - ray regime available . here , we present the detailed optical emission - line ( and simultaneous absorption line ) data over a broad wavelength range to probe the dominant ionisation processes , excitation sources , morphology and kinematics of the hot gas ( as well as the morphology and kinematics of the stars ) . this , combined with the other multiwavelength data , will form a complete view of the different phases ( hot and cold gas and stars ) and how they interact in the processes of star formation and feedback detected in central galaxies in cooling flow clusters , as well as the influence of the host cluster . we derive the optical dust extinction maps of the four nebulae . we also derive a range of different kinematic properties , given the small sample size . for abell 0496 and 0780 , we find that the stars and gas are kinematically decoupled , and in the case of abell 1644 we find that these components are aligned . for abell 2052 , we find that the gaseous components show rotation even though no rotation is apparent in the stellar components . to the degree that our spatial resolution reveals , it appears that all the optical forbidden and hydrogen recombination lines originate in the same gas for all the galaxies . based on optical diagnostic ratios ( [ oiii]/h against [ nii]/h , [ sii],6731/h , and [ oi]/h ) , all galaxies show extended liner emission , but that at least one has significant seyfert emission areas , and at least one other has significant hii like emission line ratios for many pixels . we also show that the hardness of the ionising continuum do not decrease with galactocentric distance within our field - of - view ( with the exception of one galaxy that show a core separation ) as the emission line ratios do not vary significantly with radius . this also indicates that the derived nebular properties are spatially homogeneous . we fit agn and pagb stars photoionisation models as well as shock excitation models to our derived diagnostic ratios . these fits , combined with information from multiwavelength studies reveal that agn photoionisation is the most likely ionisation mechanism in at least two cases even though shocks and pagb stars can not be conclusively eliminated . = 1 [ firstpage ] galaxies : formation galaxies : elliptical and lenticular , cd galaxies : clusters : individual : abell 0496 galaxies : clusters : individual : abell 0780 galaxies : clusters : individual : abell 1644 galaxies : clusters : individual : abell 2052

1303.0884

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we present detailed integral field unit ( ifu ) observations of the central few kiloparsecs of the ionised nebulae surrounding four active ccgs in cooling flow clusters ( abell 0496 , 0780 , 1644 and 2052 ) . our sample consists of ccgs with h@xmath0 filaments . we observed the detailed optical emission - line ( and simultaneous absorption line ) data over a broad wavelength range to probe the dominant ionisation processes , excitation sources , morphology and kinematics of the hot gas ( as well as the morphology and kinematics of the stars ) . two of the four sources have not been observed with ifu data before ( abell 0780 and 1644 ) , and for the other two sources we observed with significantly improved integration times ( and number of lines ) than previous studies ( hatch et al . 2007 , edwards et al . 2009 ) . this will help form a complete view of the different phases ( hot gas and stars ) and how they interact in the processes of star formation and feedback detected in central galaxies in cooling flow clusters , as well as the influence of the host cluster . the total extinction maps are presented in figure [ fig : mcg_extinct ] and shows extinction which agrees well with previously derived long - slit values ( where available ) . from long - slit spectra , crawford et al . ( 1999 ) derived the total extinction of pgc044257 as 0.46 to 0.63 mag . this agrees with the extinction we derived for the very centre of the galaxy in figure [ fig : mcg_extinct ] , but on average our spatially resolved extinction is slightly lower ( 0.195 mag ) . crawford et al . ( 1999 ) derived an integrated internal extinction of @xmath23 of 0.22 mag for the centre of ugc09799 . this corresponds very well to what we derived and plotted in figure [ fig : mcg_extinct ] , although we find that some regions show much higher internal extinction ( on average 0.42 mag ) . we derive a range of different kinematic properties , given the small sample size . for abell 0496 and 0780 , we find that the stars and gas are kinematically decoupled , and in the case of abell 1644 we find that these components are aligned . for abell 2052 , we find that the gaseous components show rotation even though no rotation is apparent in the stellar components . to the degree that our spatial resolution reveals , it appears that all the optical forbidden and hydrogen recombination lines originate in the same gas for all the galaxies . all galaxies show important liner emission , but that at least one has significant seyfert emission areas , and at least one other has significant hii like emission line ratios for many pixels ( consistent with the long - slit observations of mcdonald et al . ( 2012 ) ) . we also show that the hardness of the ionising continuum does not decrease with galactocentric distance ( except for pgc044257 which show an interesting core separation of the emission in the very centre of the galaxy in figure [ fig : ugc_bpt]a ) . the radial profiles of diagnostic line ratios , [ oiii]@xmath15007/h@xmath2 and [ nii]@xmath16584/h@xmath0 , show that they are roughly constant with radius for three of the four galaxies ( all except pgc044257 ) . this indicates that the dominant ionising source is not confined to the nuclear region in the two objects and that the ionised gas properties are homogeneous in the emission - line regions across each galaxy . overall , it remains difficult to dissentangle the dominant photoionisation mechanisms , even with more line measurements . the agn photoionisation models ( with higher metallicity ) are the best able to reproduce our spatially - resolved line ratios the in all of the three bpt diagrams simultaneously of most objects , even though shock models and pagb stars can not be conclusively eliminated . we also do not see extended [ oi]@xmath16300 emission , following the morphology of the strong emission lines ( e.g. farage et al . 2010 ) , therefore , it is unlikely that shock excitation is the dominant ionising source in the galaxies of this limited sample . in addition , multiwavelength observations ( as discussed in the previous section ) favour the agn photoionisation mechanism , especially in the case of pgc026269 and ugc09799 .

we present detailed integral field unit ( ifu ) observations of the central few kiloparsecs of the ionised nebulae surrounding four active central cluster galaxies ( ccgs ) in cooling flow clusters ( abell 0496 , 0780 , 1644 and 2052 ) . our sample consists of ccgs with h filaments , and have existing data from the x - ray regime available . here , we present the detailed optical emission - line ( and simultaneous absorption line ) data over a broad wavelength range to probe the dominant ionisation processes , excitation sources , morphology and kinematics of the hot gas ( as well as the morphology and kinematics of the stars ) . this , combined with the other multiwavelength data , will form a complete view of the different phases ( hot and cold gas and stars ) and how they interact in the processes of star formation and feedback detected in central galaxies in cooling flow clusters , as well as the influence of the host cluster . we also derive a range of different kinematic properties , given the small sample size . for abell 0496 and 0780 , we find that the stars and gas are kinematically decoupled , and in the case of abell 1644 we find that these components are aligned . for abell 2052 , we find that the gaseous components show rotation even though no rotation is apparent in the stellar components . to the degree that our spatial resolution reveals , it appears that all the optical forbidden and hydrogen recombination lines originate in the same gas for all the galaxies . we also show that the hardness of the ionising continuum do not decrease with galactocentric distance within our field - of - view ( with the exception of one galaxy that show a core separation ) as the emission line ratios do not vary significantly with radius . this also indicates that the derived nebular properties are spatially homogeneous . we fit agn and pagb stars photoionisation models as well as shock excitation models to our derived diagnostic ratios . these fits , combined with information from multiwavelength studies reveal that agn photoionisation is the most likely ionisation mechanism in at least two cases even though shocks and pagb stars can not be conclusively eliminated . = 1 [ firstpage ] galaxies : formation galaxies : elliptical and lenticular , cd galaxies : clusters : individual : abell 0496 galaxies : clusters : individual : abell 0780 galaxies : clusters : individual : abell 1644 galaxies : clusters : individual : abell 2052

we present detailed integral field unit ( ifu ) observations of the central few kiloparsecs of the ionised nebulae surrounding four active central cluster galaxies ( ccgs ) in cooling flow clusters ( abell 0496 , 0780 , 1644 and 2052 ) . our sample consists of ccgs with h filaments , and have existing data from the x - ray regime available . here , we present the detailed optical emission - line ( and simultaneous absorption line ) data over a broad wavelength range to probe the dominant ionisation processes , excitation sources , morphology and kinematics of the hot gas ( as well as the morphology and kinematics of the stars ) . this , combined with the other multiwavelength data , will form a complete view of the different phases ( hot and cold gas and stars ) and how they interact in the processes of star formation and feedback detected in central galaxies in cooling flow clusters , as well as the influence of the host cluster . we derive the optical dust extinction maps of the four nebulae . we also derive a range of different kinematic properties , given the small sample size . for abell 0496 and 0780 , we find that the stars and gas are kinematically decoupled , and in the case of abell 1644 we find that these components are aligned . for abell 2052 , we find that the gaseous components show rotation even though no rotation is apparent in the stellar components . to the degree that our spatial resolution reveals , it appears that all the optical forbidden and hydrogen recombination lines originate in the same gas for all the galaxies . based on optical diagnostic ratios ( [ oiii]/h against [ nii]/h , [ sii],6731/h , and [ oi]/h ) , all galaxies show extended liner emission , but that at least one has significant seyfert emission areas , and at least one other has significant hii like emission line ratios for many pixels . we also show that the hardness of the ionising continuum do not decrease with galactocentric distance within our field - of - view ( with the exception of one galaxy that show a core separation ) as the emission line ratios do not vary significantly with radius . this also indicates that the derived nebular properties are spatially homogeneous . we fit agn and pagb stars photoionisation models as well as shock excitation models to our derived diagnostic ratios . these fits , combined with information from multiwavelength studies reveal that agn photoionisation is the most likely ionisation mechanism in at least two cases even though shocks and pagb stars can not be conclusively eliminated . = 1 [ firstpage ] galaxies : formation galaxies : elliptical and lenticular , cd galaxies : clusters : individual : abell 0496 galaxies : clusters : individual : abell 0780 galaxies : clusters : individual : abell 1644 galaxies : clusters : individual : abell 2052

astro-ph9701036

i

the study of the stellar populations and the distribution of metallicities plays an important role in our understanding of the star formation history of the galaxies . their stellar populations are expected to be more complex than those of , for example , globular clusters , which are thought to be composed of a single stellar population . in fact , burstein _ et al . _ ( 1984 ) found differences when comparing colors and spectroscopic features of globular clusters with galaxies . key parameters in the interpretation of the observed colors and the line - strengths are the metallicity and the age . the problem is that even in the simplest unresolved stellar systems their effects are very difficult to separate using only colors ( oconnell 1986 , renzini 1986 , buzzoni _ et al . _ 1992 ) . using colors together with absorption lines more accurate conclusions can be drawn . although every absorption line strength is dependent on different kinds of stars , in principle it should be possible to determine average metallicities or ages by carefully selecting features which more sensitive to the metallicity and others which are more sensitive to the age ( e.g. worthey _ et al . however the abundances of some elements may well evolve differently from those of others ( e.g. @xmath3-enhancement ) , and the conversion of ages and metallicities through models to observed colors and indices may be not unique due to problems in e.g. stellar evolution theory . finally , the large velocity broadening in giant elliptical galaxies implies that only the strongest lines can be used to obtain physical information from their spectra . in the process of understanding the stellar population of early - type galaxies we first developed a new spectrophotometric model , which can be used to interpret observed colors and absorption lines of galaxies ( vazdekis _ et al . _ 1996 , hereafter paper i ) . the model is based on the latest improvements in stellar evolution theory and on the most recent stellar libraries . instead of studying a large sample of galaxies using a few lines indices , as has been done before ( e.g. worthey _ et al . _ 1992 , gonzalez 1993 ) , we preferred to obtain high quality observations of three representative early - type galaxies ( two giant ellipticals and the bulge of the sombrero galaxy ) , but in many colors and absorption lines , and to make very detailed fits to each index , to understand better global ages and metallicities , and also to follow the abundances of individual elements . such analysis now is possible , since we could calibrate our observations using the large sample of stars from the extended lick - system ( worthey _ et al . _ ( 1994 ) hereafter wfgb ) . in this paper we have applied our spectrophotometric population synthesis model following both the single - age single - metallicity and the chemical evolutionary approaches . we address here the problem of whether the conclusions we obtain depend on the stellar population synthesis method we use . in the end we find that the use of many indices does yield interesting information , and we show that we can learn more than by using only a few indices , as has been done in the past . at the same time we study the stellar population gradients in the three galaxies . this paper is organized as follows : in section 2 we explain our observations and the method we use to derive the line - strengths . in section 3 we fit our population synthesis model and discuss the results obtained by fitting the data . finally in section 4 we present our conclusions .

_ 1996 ) to new high quality observational data of the nuclear regions of two representative elliptical galaxies and the bulge of the sombrero galaxy . here we fit in detail absorption lines and 6 optical and near - infrared colors following two approaches : fitting a single - age single - metallicity model and fitting our full chemical evolutionary model .

we present here the results of applying a new chemo - evolutionary stellar population model developed by ourselves in a previous paper ( vazdekis _ et al . _ 1996 ) to new high quality observational data of the nuclear regions of two representative elliptical galaxies and the bulge of the sombrero galaxy . here we fit in detail absorption lines and 6 optical and near - infrared colors following two approaches : fitting a single - age single - metallicity model and fitting our full chemical evolutionary model . we find that all of the iron lines are weaker than the best fitting models predict , indicating that the iron - abundance is anomalous and deficient . we also find that the ca index at is much lower than predicted by the models . we can obtain good fits for all the other lines and observed colors with models of old and metal - rich stellar populations , and can show that the observed radial gradients are due to metallicity decreasing outward . we find that good fits are obtained both with fully evolutionary models and with single - age single - metallicity models . this is due to the fact that in the evolutionary model more than 80% of stars form within 1.5 gyr after the formation of the galaxies . the fact that slightly better fits are obtained with evolutionary models indicates these galaxies contain a small spread in metallicity .

astro-ph9701036

c

we have obtained high quality observations of almost the whole set of line - indices of the extended lick - system for three representative early - type galaxies , and have applied a new spectrophotometric chemo - evolutionary population synthesis model developed by ourselves in a previous paper ( paper i ) . we can make models which give good fits in all the colors and many of the most important line - indices . these fits however can not synthesize quantitatively a number of lines primarily from fe and ca . we find that 6 independent fe lines are too weak compared to lines of all other elements indicating that the iron - abundance is anomalous and deficient in the radial range of the galaxies that we studied . this implies that the global metallicity inferred must depend on whether we use magnesium or iron lines as the prime indicators . invoking @xmath3-enhancement one can obtain better fits for the iron lines , but other features such as nad then become worse if we follow the abundance ratios given in weiss _ et al _ ( 1995 ) . finally we find that the ca4227 is much fainter than predicted by the models . in general we find that the three galaxies require metallicities higher than solar for the inner regions while the ages are older than 10 gyr , and the observed radial gradients are due to metallicity decreasing outward . we also find that ngc 4472 is more metal - rich , than the other two galaxies . to fit this set of galaxies with the full chemical evolutionary population synthesis model we used the variable imf scenario ( defined in paper i ) which invokes an imf skewed towards high - mass stars in the begining , during a short period of time ( smaller than 1 gyr . ) , and towards low - mass stars later for the remaining time . the best fits indicate that dwarfs contribute @xmath117 to the u band , @xmath118 in v band and @xmath119 in k band . we find that slightly better fits are being obtained with the chemical evolutionary model than with the single - age , single - metallicity model , justifying the extra complications . however , since the predicted spread in metallicities is not very large , and since the bulk of the stars were formed at the very early stages of the galactic evolution ( at age lower than @xmath120 ) we conclude that the single - age single - metallicity stellar population models offer reasonable first order fits to this kind of stellar systems , especially if one wishes to avoid comprobational complexity . this study shows that it would be useful to extend the present analysis to include other features at shorter wavelengths in the uv region such as the indices of rose ( 1994 ) , and to the near - ir with indices such as na@xmath1 at @xmath121 , the ca@xmath68 triplet and the co or h@xmath15o features . to understand the stellar populations of the early - type galaxies and to e.g. disentangle age and metallicity ( jones & worthey 1995 ) , bressan _ et al . _ 1995 ) it will be important to introduce as many constraints as possible , by observing the galaxies in many calibrated absorption lines . we are indebted to the referee , j. gonzalez , who have done a very thorough work on our first version as a result of which the present paper have been greatly improved . we are grateful to j. gorgas for providing us with a set of observational results before publication . we also thanks a. weiss for his comments . this work was partially supported by grants pb91 - 0510 and pb94 - 1107 of the spanish dgicyt . arimoto , n. , & yoshii , y. , 1986 , , 164 , 260 arimoto , n. , & yoshii , y. , 1987 , , 173 , 23 bertelli , g. , bressan , a. , chiosi , c. , fagotto , f. & nasi , e. , 1994 , , 106 , 275 boroson , t. & thompson , i. , 1991 , , 101,111 bressan , a. , chiosi , c. , fagotto , f. , 1994 , , 94 , 63 bressan , a. , chiosi , c. & tantalo , r. , 1996 , , 311 , 425 bottema , r. , 1988 , , 197 , 105 burstein , d. , faber , s. m. , gaskell , c. m. & krumm , n. , 1984 , , 287 , 586 burstein , d. , davies , r.l . , dressler , a. , faber , s.m . , stone , r.p.s . lynden - bell , d. , terlevich , r. & wegner , g. , 1987 , 1987 , , 64 , 601 buzzoni , a. , gariboldi , g. & mantegazza l. , 1992 , , 103 , 1814 casuso , e. , vazdekis , a. , peletier , r. & beckman , j.e . , 1996 , , 458 , 533 davies , r.l . , efstathiou , g. , fall , s.m . , illingworth , g. , schechter , p.l . , 1983 , , 266 , 41 davies , r.l . , sadler , e.m . & peletier , r.f . , 1993 , , 262 , 650 daz , a. , terlevich , e. & terlevich , r. , 1989 , , 239 , 325 faber , s.m . & french , h.b . , 1980 , , 235 , 405 fisher , d. , franx , m. & illingworth , g. , 1995 , , 448 , 119 gonzalez , j.j , 1993 , phd . thesis , university of lick , santa cruz , california gonzalez , j.j . , gorgas , j. , 1996 , in _ fresh views on elliptical galaxies _ , eds . buzzoni , a. , renzini , a. , a. serrano , asp conf . ser . , 86 , 225 . goudfrooij , p. & emsellem , e. , 1996 , a&a , 306 , l45 he s , r. & peletier , r. , , 268 , 539 jones , l. & worthey , g. , 1995 , , 446 , 31 kormendy , j. , 1988 , , 335 , 40 oconnell , r. , 1976 , , 206 , 370 oconnell , r. , 1986 , in stellar populations , ed . c. norman , a. renzini and m. tosi , cambridge university press , p. 167 peletier , r.f . , 1989 , d. thesis , univ . of groningen peletier , r.f . , davies , r.l . , illingworth , g.d . , davis , l.e . & cawson , m. , 1990a , , 100 , 1091 peletier , r.f . , valentijn , e.a . & jameson , r.f . , 1990b , , 233 , 62 pickles , a.j . , 1985 , , 296 , 340 rich , r.m . , 1988 , , 95 , 828 renzini , a. , 1986 , in stellar populations , ed . c. norman , a. renzini and m. tosi , cambridge university press , p. 213 rieke , g.h . & lebofsky , m.j . , 1985 , , 288 , 618 rose , j.a . , 1984 , , 89,1238 rose , j.a . , 1994 , , 107,206 saglia , r.p . , bertin , g. , bertola , f. , danziger , j. , dejonghe , h. , sadler , e.m . , stiavelli , m. , de zeeuw , p.t . , zeilinger , w.w . , 1993 , , 403 , 567 terlevich , e. , daz , a. & terlevich , r. , 1990 , 242 , 271 tonry , j. & davis , m. 1979 , , 84 , 1511 vazdekis , a. , casuso , e. , peletier , r. f. & beckman , j. e. , 1996 , , 106 , 307 . * paper i*. weiss , a. , peletier , r.f . & matteucci , f. , 1995 , , 296 , 73 woosley , s.e . & weaver , t. , 1995 , , 101 , 181 worthey , g. , faber , s. & gonzlez , j. , 1992 , , 398 , 69 worthey , g. , faber , s. , gonzlez , j. & burstein , d. , 1994 , , 94 , 687 . * wfgb*. worthey , g. , 1994 , , 95 , 107

we present here the results of applying a new chemo - evolutionary stellar population model developed by ourselves in a previous paper ( vazdekis _ et al . we find that all of the iron lines are weaker than the best fitting models predict , indicating that the iron - abundance is anomalous and deficient . we also find that the ca index at is much lower than predicted by the models . the fact that slightly better fits are obtained with evolutionary models indicates these galaxies contain a small spread in metallicity .

we present here the results of applying a new chemo - evolutionary stellar population model developed by ourselves in a previous paper ( vazdekis _ et al . _ 1996 ) to new high quality observational data of the nuclear regions of two representative elliptical galaxies and the bulge of the sombrero galaxy . here we fit in detail absorption lines and 6 optical and near - infrared colors following two approaches : fitting a single - age single - metallicity model and fitting our full chemical evolutionary model . we find that all of the iron lines are weaker than the best fitting models predict , indicating that the iron - abundance is anomalous and deficient . we also find that the ca index at is much lower than predicted by the models . we can obtain good fits for all the other lines and observed colors with models of old and metal - rich stellar populations , and can show that the observed radial gradients are due to metallicity decreasing outward . we find that good fits are obtained both with fully evolutionary models and with single - age single - metallicity models . this is due to the fact that in the evolutionary model more than 80% of stars form within 1.5 gyr after the formation of the galaxies . the fact that slightly better fits are obtained with evolutionary models indicates these galaxies contain a small spread in metallicity .

1102.0535

c

the wavelength region around 1 @xmath2 m is ideal for spectral classification of cttss : ( 1 ) the excess emission arising from the accretion process , which is very strong in the uv and optical wavelengths , is relatively small ; ( 2 ) the emission from the accretion disk itself , which can dominate the spectrum at k band and longer wavelengths , is minimal ; ( 3 ) the effects of any extinction are mitigated substantially compared to the optical ; and ( 4 ) there are numerous strong photospheric absorption features present that can be used for classification . the last point is particularly important because , while the contributions from the accretion shock and circumstellar disk ( uv and ir excesses , respectively ) are at a relative minimum in the y and j bands , they are not necessarily negligible and evidence for significant j band veiling has been found in some sources @xcite . however , the ratio of absorption ews , as discussed in 3.1 , provides a veiling independent method of determining the spectral type of a source . although the relatively ` clean ' nature of this spectral region has been pointed out before @xcite and exploited to study the emission associated with the accretion process in cttss @xcite , this is the first time of which we are aware that the absorption features in this region have been used for spectral classification of a ctts . the absorption line ews we measure , in comparison with those derived from the irtf library spectra , provide strong evidence that the underlying star in tw hya has a spectral type of @xmath14 m2.5v . this result suggests that the values for the stellar mass and radius typically adopted in the literature ( @xmath161 k , @xmath162 , and @xmath163 ; e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) are incorrect , as they are based on an incorrect spectral type ( k7v ) . we suggest that the appropriate values for tw hya are @xmath164 k , @xmath165 , and @xmath166 , based on an m2.5v spectral type , the temperature and mass calibrations given by @xcite and @xcite , and the estimated bolometric luminosity . the spectral type we determine , and the stellar parameters we derive , are clearly inconsistent with those found by others ( e.g. * ? ? ? * ; * ? ? ? examination of the spectra shown by @xcite indicates that the k7v spectral classification is appropriate , as tw hya clearly has an earlier type than those of the m stars shown . @xcite and @xcite fit atmosphere models to high resolution optical spectra and derived parameters again consistent with a k7v star . on the other hand , the mass estimated for tw hya from the @xcite stellar parameters is far too large for even a k7v spectral type . furthermore , the moderate resolution optical spectrum presented by @xcite ( their figure 9 ) , with its strong rise in the continuum to the red and its sharp and prominent tio bandheads near 7100 , is more suggestive of an early m dwarf than a late k dwarf ( see below ) and does not seem to be completely consistent with the spectrum presented by @xcite . can these two discrepant spectral type classifications be reconciled ? the optical spectrum of tw hya suffers from considerable and variable veiling ( see e.g. , * ? ? ? * ) , so it is possible that veiling has contributed to mis - classification , especially if the spectral comparison is restricted to very small wavelength regions lacking strong lines diagnostic of spectral type . to investigate this possibility , we selected an m2v star from the indo - us spectral library @xcite and added veiling in an attempt to reproduce a k7v star spectrum between 6400 and 7600 ( the spectral region displayed in fig . 1b of @xcite ) . we found that it was not possible unless the veiling was substantially larger ( @xmath167 ) than that estimated by either @xcite or @xcite in this wavelength range . therefore , veiling can not be completely responsible for the classification differences . we also considered the possibility that tw hya is an unresolved binary . however , given the relative luminosities of k and m stars , it is not physically possible for a coeval k7v+m2.5v binary system to generate a spectrum in which the k7v component dominates the optical spectrum but is nearly invisible in the nir spectrum . because both the continuum and line emission are know to vary substantially in tw hya , it is tempting to consider the possibility that the spectrum ( and spectral type ) of the object varies as a function of both accretion rate and wavelength . a physically plausible explanation for this variation is that the spectrum of tw hya consists of two separate components , one due to the star ( m2.5v ) and one arising from an accretion hot spot , either on the surface of the star or located in the inner disk , or from the inner disk itself . in this scenario , the hot spot or inner disk would have a temperature of @xmath168 k and would generate a spectrum similar to that of a k7v star . this component would also vary in strength with the accretion rate , dominating the ( optical ) spectrum and completely overwhelming the underlying m2.5v stellar spectrum when the accretion rate is high . support for this suggestion can be found by comparing the observed optical spectra with the reported h@xmath11 equivalent widths , a proxy for the accretion rate . the optical spectrum presented by @xcite is clearly that of a k7v star and yields an @xmath169 . similarly , the optical spectrum shown by @xcite is consistent with that of a k7v star and has @xmath170 ( c. m. johns - krull , private communication ) . the optical spectrum presented by @xcite , however , corresponds to spectral type intermediate between a k7v and an early m star , and has @xmath171 between @xmath172 and @xmath173 . in fact , when we attempted to reproduce the features seen in this spectrum we found that a combination of a k7v and an m2.5v , with roughly equal contributions at 0.8 @xmath2 m , provides a much better representation than any single k or early m spectrum alone . the shape and depth of the tio bands at 7100 and the simultaneous presence of these bands and a strong line at 7148 indicates that the observed spectrum is a composite of both a k7v and an early m type spectrum . in our nir spectrum of tw hya , the region shortward of 1@xmath2 m can also be well fit with an m2.5v spectrum and a small contribution from a k7v spectrum , comprising @xmath144% of the total flux at 0.8 @xmath2 m . this is shown in fig . [ m+k ] , where it can be seen that at wavelengths shorter than @xmath174 m we would expect that , during our observations of tw hya , the k7v spectrum contributed roughly half of the total flux , but comprised only a very small fraction of the flux longward of @xmath175 m . unfortunately a more satisfactory test of this suggestion can not be carried out with the spectra and accretion rates or ew values found in the literature . ( surprisingly few optical and nir spectra of tw hya are actually shown in the voluminous literature on this object . ) frequent simultaneous monitoring of tw hya in both the optical and nir wavelength regimes would be able to confirm or rule out our suggestion . our results for the spectral type and effective temperature require a re - evaluation of the age of tw hya . the age adopted for tw hya under the assumption of a k7v spectral type with @xmath176 k is often @xmath18 myr , derived by comparing the location of tw hya in the hr diagram with model isochrones ( e.g. * ? ? ? * ) . in fig . [ hrd ] , we plot the location of tw hya on the h - r diagram , using our estimated @xmath177 , along with the model tracks and isochrones of @xcite , @xcite , @xcite , and @xcite . despite the considerable variation in the model predictions , all of the models yield masses smaller than our adopted value of @xmath178 and ages substantially younger than the canonical value of 10 myr . large underestimates of both mass and age by the various models have been pointed out previously by @xcite . however , even accounting for an underestimate of the age by a factor perhaps as large as two @xcite would be insufficient to make the star 10 myr old . the models of @xcite provide a mass of @xmath179 , closest to our adopted value of @xmath178 . for these models , the age of tw hya estimated from the isochrones is @xmath3 myr . we note that the new location of tw hya on the h - r diagram actually brings this source into better agreement with other members of the twa , as can be seen from fig . 3 of @xcite , which indicates that , aside from twa 6 and twa 9 a and b , the locations of the members of the twa on the h - r diagram are consistent with an isochrone age for the association of @xmath180 myr . this age is also in reasonable agreement with the expansion age of the twa of @xmath181 myr derived by @xcite , and therefore alleviates to a considerable degree the previous discrepancy between the isochrone age of twa and dynamical age estimates . furthermore , compared to the usually adopted age of 10 myr , an age of 3 - 5 myr for tw hya is in much better agreement with estimates of the half life of accretion disks in low mass stellar systems of @xmath182 myr @xcite . by 10 myr the disks in such systems have usually transformed into debris disks with masses of @xmath183 @xcite . the large mass of the disk in tw hya ( @xmath184 * ? ? ? * ) therefore suggests an age of considerably less than 10 myr @xcite , in agreement with our much younger estimate . we also note that tw hya exhibits many of the same emission features , and has exactly the same li 6708 absorption ew , as the m2.5 star gn tau @xcite . the latter star is a low - mass t tauri star with an estimated age of @xmath3 myr , again providing support for our age estimate for tw hya . the determination of an accurate spectral type permits the subtraction of the correct spectral template to reveal the emission from the accreting gas and the circumstellar disk . under the assumption that the h lines are optically thin and follow the case b predictions , our analysis of the h line flux ratios yields a temperature of @xmath185 k , a density of @xmath186 @xmath7 and a thickness of the emission column of @xmath187 km . comparison of our results with those presented by @xcite , who modeled the emission from the accreting column of gas in the magnetospheric infall scenario , reveals surprisingly good agreement for some of the physical parameters . the models of @xcite include emission from the shock and post - shock region , the pre - shock region , and the heated stellar atmosphere . the emission properties of the models are parametrized in terms of the energy flux carried by the accretion column into the shock , @xmath188 , given by @xmath189 the h line emission in these models arises from the pre - shock region , which is predicted to have a density given by @xmath190 for the stellar parameters for tw hya given above , these equations give @xmath191 erg @xmath123 s@xmath17 and @xmath192 @xmath7 . the latter value is fairly close to our empirical results ( under the assumption that all of this material becomes fully ionized in the pre - shock region ) . the models also predict a temperature for this region of @xmath193 k , and thickness of the fully ionized zone of @xmath194 km , again in good agreement with our findings . recently @xcite has used interferometry to determine the stellocentric radii of the br @xmath13 emitting gas in t tauri and herbig ae / be stars . they find that the emission in general arises from gas within 0.01 au ( @xmath195 km ) , an upper limit that our results certainly satisfy . the infall velocity in the models of @xcite is predicted to be @xmath196 or @xmath197 for the mass and radius we derive for tw hya , in excellent agreement with the velocities corresponding to the observed inverse p cygni absorption features seen in our h and 1.083@xmath2 m line profiles . using our derived density and placing a limit on the optical depth of the pa @xmath12 line , we derive a lower limit to the fractional area covered by the accretion column of @xmath198 . our limit is well within the range of previous estimates of the covering fraction , for both tw hya itself as well as other cttss @xcite . although our limit is a factor of 7 larger than that estimated by @xcite , we also derive substantially larger ( factors of 4 - 5 ) values of the accretion luminosity and rate than these authors . ( @xcite also derive a substantially larger value of the accretion energy flux @xmath188 than we do , largely because of this difference in the values of the covering fractions @xmath109 . ) if the covering fraction is correlated with the accretion rate , as claimed by @xcite , then the considerably larger accretion rates we measure compared to @xcite should be associated with a larger covering fraction . it is interesting to note that the values of the energy flux and covering fraction we derive for tw hya are very similar to those found by @xcite for cy tau , the star whose 1.083 @xmath2 m line profile resembles that in our spectrum of tw hya most closely . despite the good agreement between our temperature and density estimates and the model predictions of @xcite , our values do not agree with those of @xcite for their sample of cttss , and our analysis rules out their values for tw hya with high confidence . @xcite do not present results for individual stars , so it is unclear how much variation they find from object to object . the mass accretion rates listed for the objects in their sample are substantially higher than that measured for tw hya . ( the minimum value listed in their table is more than double the value derived for tw hya in 3.2.1 from the pa @xmath12 line and five times larger than that derived from the br @xmath13 line . ) however , one would expect that higher mass loss rates would generate larger volume densities . at the moment , we have no satisfactory explanation for this discrepancy . the high densities we derive provide a reasonable explanation for why other lines typical of ionized regions ( e.g. , forbidden lines of and ) are weak or absent in optical and nir spectra of tw hya obtained with narrow slits centered on the star ( e.g. , * ? ? ? * ) . since these ionization states are found primarily within the region where h is fully ionized and the density is well above the critical density for these transitions , the ground - state levels giving rise to these transitions are collisionally de - excited . spectra obtained with wide slits , encompassing lower density regions farther from the star , might be expected to reveal the usual forbidden lines ( see e.g. , * ? ? ? our analysis suggests that the lines seen in the nir spectrum are produced by ly @xmath12 fluorescence . it is not immediately obvious , however , where the emission is generated . @xcite demonstrated that the profile of the 0.8446 line correlates with that of pa 11 in a small sample of cttss , and therefore suggested that the lines were formed in a common region . furthermore , the lines in our spectrum of tw hya are unresolved at our resolution , which indicates that they are not arising from a region experiencing substantial infall or outflow , and therefore it is tempting to suggest that they are formed at the base of the accretion column , along with the h lines . however , production of the lines by ly @xmath12 fluorescence requires a high ly @xmath12 flux density in a region that contains neutral oxygen . the latter requirement is inconsistent with completely ionized h gas in the pre - shock region in the models of @xcite . a partially ionized region at the outer edge of the pre - shock region could be responsible for the emission . this region could also give rise to the [ ] 6300 , 6363 lines that are seen in the optical spectrum @xcite . however , fluorescence also requires a large optical depth in the balmer transitions . using the equation given by @xcite for the escape probability of h@xmath11 , @xmath199 and that by @xcite for the optical depth @xmath200 in terms of @xmath199 , we derived a rough estimate of the h@xmath11 optical depth of @xmath201 . such a large optical depth in h@xmath11 seems incompatible with the finding that the observed h line strength ratios are well reproduced by the theoretical case b values ( see also * ? ? ? * ) , which assumes that all transitions above the ly series are optically thin . a more detailed model of the emission line region and its spectrum will be needed to resolve this puzzle . finally , our derived nir excess flux spectrum , usually interpreted as arising from the hot inner accretion disk , does not match that from any recent model of tw hya . while the h - band peak in our excess flux spectrum suggests a dust temperature of @xmath150k , which would be expected for dust in the inner disk , the sharp drops in flux at both shorter and longer wavelengths are not reproduced by current optically thin disk models . in fact , as discussed above , we suspect that most of this excess emission does not arise from the inner accretion disk , but is rather due to the lower h@xmath202 opacity in the star s atmosphere relative to that of an older , higher gravity field dwarf . therefore , during our observations , any nir emission from the hot inner accretion disk must have been very small , much smaller than either previous estimates or the predictions of current models . it is possible that previous values of the nir excess have been overestimated as a result of both the adoption of an incorrect spectral type for tw hya , as well as the spectral differences due to differences in the opacity , gravity , and age between tw hya and any comparison field dwarf . matching a library template with a spectral type earlier than m2v to the short wavelength end of the nir spectrum would yield substantially more excess emission at wavelengths @xmath203 @xmath2 m than we estimate . in addition , scaling earlier spectral type templates to match the observed tw hya flux levels between 0.95 and 1.34 @xmath2 m yields an excess spectrum for which synthetic photometry is in reasonable agreement with some of the models ( e.g. * ? ? ? nevertheless , in these cases the resulting excess flux spectra appear to be unphysical ( because of negative values ) , and are certainly not the smooth blackbody functions characterized by a single dust temperature expected from the models or observed in other ctts sources ( e.g. * ? ? ? we caution that any attempts to determine the nir excess emission arising from accretion disks around young stellar objects similar to tw hya must account for any possible differences in age and gravity between the target objects and the spectral templates . failure to do so could lead to spurious results . as we have shown here , the use of an old , higher gravity field dwarf as a spectral template can lead to an excess spectrum that primarily reflects differences in the h@xmath202 atmospheric opacity between the ctts and the template , not the emission from an accretion disk .

we derive an excess spectrum ( above that of the m2.5v template ) that peaks in the h band . although our derived veiling values , , agree with previous estimates , the excess spectrum does not match that of current models in which this flux is generated by an inner optically thin disk . we suggest that the excess flux spectrum instead reflects the differences in atmospheric opacity , gravity , and age between tw hya and older , higher gravity field m2.5 dwarfs .

we present high signal - to - noise , moderate spectral resolution ( ) near - infrared ( m ) spectroscopy of the nearby t tauri star tw hya . by comparing the spectrum and the equivalent widths of several atomic and molecular features with those for stars in the irtf near - infrared library , we revise the spectral type to m2.5v , which is later than usually adopted ( k7v ) . this implies a substantially cooler stellar temperature than previously assumed . comparison with various pre - main sequence models suggests that tw hya is only myr old ; much younger than the usually adopted myr . analysis of the relative strengths of the h lines seen in the spectrum yields estimates for the temperature and density of the emitting region of k and . the thickness of the emitting region is km and the covering fraction is . our derived physical parameter values agree with the predictions of the magnetospheric accretion scenario . the highest signal - to - noise h lines have profiles that indicate multiple emission components . we derive an excess spectrum ( above that of the m2.5v template ) that peaks in the h band . although our derived veiling values , , agree with previous estimates , the excess spectrum does not match that of current models in which this flux is generated by an inner optically thin disk . we suggest that the excess flux spectrum instead reflects the differences in atmospheric opacity , gravity , and age between tw hya and older , higher gravity field m2.5 dwarfs .

astro-ph9612079

r

when the interferometer is scanning the object , the monochromatic emission of this latter is modulated by the interference pattern while the continuum emission remains unaffected . this enables to distinguish line and continuum emission with a much higher contrast than with simple images obtained through interference filters . figures 1 and 2 show the logarithmic contour maps of respectively the red continuum emission and the monochromatic h@xmath0 emission in absolute flux units across the main body of izw18 . the selectivity of the fabry - prot interferometer due to its high finesse ( f=16 measured on calibration frames ) allows a very clear separation of the line and the continuum emissions . furthermore , the overall system ( fp + focal reducer ) benefits from a very low level of scattered light , much below a percent , which ensures that the continuum map is free from additional line emission . in red continuum ( fig.1 ) the morphological structure of izw18 is complex and new details appear which were not detected by dkf89 . some of these details have their counterparts on the hst wfpc2 frames ( ht95 ) . in the main body of the galaxy besides two known nw and se red continuum components ( dkf89 ) a third one ( a ) is observed half way between them close from the north of the hii region number 6 in ht95 . we identify two other condensations : ( b ) to the north and ( c ) to the north - west of the nw compact red component . among all the components nw dominates in size , surface and absolute brightness . table 1 lists @xmath10@xmath0 , @xmath10@xmath11 positions of the photometric center of the components in arcsec with respect to the nw component . positive values of @xmath10@xmath0 are to the east and positive @xmath10@xmath11 to the north , effective diameters d in parsecs , surface brightness sb in units of 10@xmath12ergs @xmath13 and red magnitudes at 6600 . table 1 also lists the same parameters for the zwicky s `` flare '' ( zwicky 1966 ) - noted as the c satellite by dkf89 and dh90 . cccccc @xmath14 & @xmath15 & @xmath16 & @xmath17 & @xmath18 & @xmath19 + & & & & + @xmath20 & 0 & 0 & 112 & 4.8 & 17.2 + @xmath21 & 2.9 & -3.6 & 79 & 3.1 & 18.7 + @xmath22 & 1.5 & -1.5 & 56 & 3.2 & 19.2 + @xmath23 & -0.7 & 2.9 & 56 & 2.8 & 19.1 + @xmath24 & -2.9 & 1.5 & 40 & 4.0 & 20.2 + @xmath25 & -18.9 & 16.7 & 177 & 0.3 & 20.6 + the comparison between the structure of the nw red component and its surroundings with that of ht95 frames shows that this component is coeval to an isolated hii region south to the main nw star - forming complex ( ht95 ) . a sharp cut - off in the nw red continuum brightness distribution is observed towards the ( a ) and se components while it fades smoothly in the opposite direction towards the ( b ) component . the ( b ) component itself is located in the northern part of nw star forming complex of ht95 . at faint levels of brightness a west side `` ledge '' is observed . the ( c ) component is embedded into this ledge and has no direct counterpart on hst frames ( ht95 ) . besides the main body of the galaxy its outer envelope is also radiating in the red continuum . this radiation is not homogenous . it shows a clumpy structure extending to the ne direction up to a distance of about 740 pc from the nw component . its patterns are located within the same region of the ne h@xmath0 shell of m96 . towards the sw the red continuum radiation extends in more homogeneous way by curving at its end to the west and its patterns closely follow the h@xmath0 arc like structure dh90 . stellar light as well as some nebular continuum contribute to the red continuum radiation of the outer envelope of the galaxy and its arc - like structure . to determine their respective contribution we have measured the l(h@xmath0)/l(6600 ) ratios across these regions and compared the obtained values with model calculations provided to us by mas - hesse ( private communication ) . models show that the underlying nebular continuum should be less than 1 percent of our measured luminosity at 6600 . our h@xmath0 monochromatic image ( fig.2 ) completely reproduces the structural features which were identified in earlier observations ( hua et al . 1987 ; dkf89 ; dh90 ; ht95 ; m96 ; ostlin et al . let us underline some details . we hereafter shall define an autonomous hii feature as the region which is inside its outermost closed contour . both nw and se condensations are isolated from the main body of the galaxy by an isophote corresponding to 4.5 10@xmath26 ergs @xmath27 arcsec@xmath28 of surface brightness . the nw component of izw18 has a size of 195 x 117 pc@xmath29 , while the se component is 157 x 117 pc@xmath29 . note that the elongation of both components coincides with the elongation of the main body of the galaxy . after correction from galactic reddening the integrated h@xmath0 flux of nw and se components come to be 1.3 10@xmath30 ergs @xmath31 and 6.3 10@xmath32 ergs @xmath27 respectively . at d = 10 mpc these values correspond to h@xmath0 luminosities of 1.6 10@xmath33ergs @xmath34 and 7.6 10@xmath35ergs @xmath1 . assuming case b conditions and t@xmath7 = 18000 k ( dufour et al . 1988 ) these luminosities require conversion of 2.2 10@xmath36 and 1.1 10@xmath36 ionizing photons @xmath1 requiring 47 and 23 o5v stars , assuming that an o5v star emits 4.7 10@xmath37 photons @xmath1 ( osterbrock 1989 ) . star formation rates ( from 0.1 to 100@xmath38 ) in the nw and se component are equal respectively to 4.7 10@xmath39@xmath38yr@xmath2 pc@xmath28 and 2.9 10@xmath39@xmath38yr@xmath2 pc@xmath28 assuming a salpeter initial mass function ( hunter & gallagher 1986 ) . masses for the ionized gas in the nw and se components have been estimated to be m(hii ) = 7.3 10@xmath40@xmath38 for the nw condensation and m(hii ) = 3.4 10@xmath40@xmath38 for the se one , but these standard estimates are only indicative since these hii regions are far from being homogeneous as seen from the hst images . the analysis of the mean spatial profiles of both components along the direction of their elongation and perpendicular to it , shows that the surface brightness peak of the nw h@xmath0 component is about 7.0 10@xmath26ergs @xmath27 arcsec@xmath28 , as compared to 6.4 10@xmath26ergs @xmath27 arcsec@xmath28 for the se component . the h@xmath0 surface brightness gradient on the nw component across two perpendicular directions is different . it is gently sloping across the major axis of the component and much steeper in the perpendicular direction where according to ht95 a gap in ionized gas distribution is observed . the smoothest gradient is observed along the tail extending to the nw and wraps around to the west of the component . this feature was noted by dkf89 , dh90 and also traced in the h@xmath0 maps of hua et al . it is very well seen in fig.1b of m96 and shows its detailed structure in fig . 3 of ht95 . as regards to the se compact component , its h@xmath0 line brightness distribution is more homogeneous . an interesting h@xmath0 feature is seen as a prominent winding ridge ( dh90 ; ht95 ; m96 ; ostlin et al . 1996 ) which expands south from the se hii compact component , bends around to the nw , then turns back to the ne , making an half wrapping around the nw hii compact component . in the nw direction from the north - western boundary of the ridge about the same distance as from the nw component lies zwicky s `` flare '' ( zwicky 1966 ) . the ridge as an isolated structure is well shaped and has a conspicuous clumpy structure ( ht95 ) . as mentioned above ( sec.3.1 ) several patterns of the ridge radiate some red continuum . the continuum patterns do not follow the h@xmath0 clumps distribution . to understand the nature of the ridge we carefully tested the possibility of its link to the se compact component . we conclude that there is not direct connection between them . from this point of view the ridge can be an isolated feature in the system . as it is noted by viallefond et al . ( 1987 ) the two major star forming areas in the main body of izw18 are offset to the east of the double - lobed hi emission peak . the ridge wraps around the hi distribution peak opposite to the side where the main body of the galaxy is located , roughly following the steep contours marking the edge of the hi concentration . figure 3 shows the h@xmath0 image of the galaxy with the 6600 red continuum contours overlaid . one sees that the centroid of the nw h@xmath0 emission is located in the plateau , between the nw and ( b ) red continuum peaks and is displaced to the north of at 1.5 ( 72pc ) from nw red continuum peak . as it was mentioned above ( sec . 3.1 ) the nw red component lies on an isolated stellar cluster - hii region complex ( ht95 ) . the ( b ) red peak is located on the nw h@xmath0 emission region and its connection with this star forming region is more evident . the centroid of the se compact h@xmath0 component is displaced by 1.0 ( 48pc ) to the west of the se red continuum centroid . this displacement between the continuum and h@xmath0 images is also evident from fig.17 of ht95 . the h@xmath0 emission extends towards the ne and sw directions from the main body of izw18 up to distance of about 1.2 kpc . the same order of extension is detected by dh90 and m96 . as we stress in sec.3.1 in the same direction but for smaller distances the clumpy red continuum emission was detected . the extended envelope detected in h@xmath0 line is not simply diffuse and shows numerous condensations ( dh90 ) . we suggest that the isolated condensations that have been identified in the extended envelope of izw18 as well as in the ridge are bonafide hii regions . this suggestion is supported by : + - the presence of clumpy red continuum radiation of stellar origin in the same fields where hii regions were identified . - the detection of individual stars in the vicinity of the hii regions fields ( table 2 of ht95 ) . - the existence of nearly 15 well isolated hii regions in the main body of the galaxy also reported by ht95 . since the h@xmath0 luminosity of any individual condensation is low ( see below ) the spectral type of the ionizing stars can not be much earlier that b0 ( osterbrock 1989 ) . at the distance of izw18 such a star has a u magnitude equal to 25.4 which is roughly the limiting magnitude for the f336w frame of ht95 . nevertheless we carefully examined the positions of each individual hii regions to find such stars using the f336w frames of the hst wfpc2 kindly given to us by deidre hunter . no such stars were found . cccccc # & @xmath10@xmath41 & @xmath10@xmath11 & @xmath17 & @xmath42 & @xmath43 + & & & & & + 1 & 10.9 & -2.2 & 56 & 0.65 & 0.78 + 2 & 10.2 & 0.0 & 97 & 1.75 & 2.11 + 3 & 10.2 & 4.4 & 97 & 6.57 & 7.89 + 4 & 8.7 & 0.7 & 40 & 0.77 & 0.92 + 5 & 6.5 & 15.2 & 56 & 1.68 & 2.01 + 6 & 4.4 & -10.9 & 56 & 0.54 & 0.64 + 7 & 3.6 & -11.6 & 40 & 0.65 & 0.78 + 8 & 3.6 & 5.1 & 56 & 6.27 & 7.52 + 9 & 3.6 & 13.1 & 97 & 2.67 & 3.21 + 10 & 2.9 & 18.9 & 69 & 2.71 & 3.25 + 11 & 2.2 & 6.5 & 40 & 3.48 & 4.17 + 12 & 2.2 & 20.3 & 56 & 2.37 & 2.84 + 13 & 1.5 & -16.7 & 97 & 4.55 & 5.46 + 14 & 1.5 & 18.9 & 40 & 1.68 & 2.01 + 15 & 0.7 & -13.8 & 40 & 1.49 & 1.79 + 16 & 0.0 & -8.7 & 40 & 6.69 & 8.03 + 17 & 0.0 & 15.2 & 56 & 2.06 & 2.47 + 18 & -0.7 & -14.5 & 79 & 3.97 & 4.77 + 19 & -0.7 & -10.9 & 69 & 7.03 & 8.44 + 20 & -1.5 & 10.9 & 112 & 7.19 & 8.62 + 21 & -1.5 & 13.1 & 69 & 1.75 & 2.11 + 22 & -2.2 & -17.4 & 56 & 2.79 & 3.35 + 23 & -2.9 & -13.8 & 97 & 9.48 & 11.30 + 24 & 88.0 & -7.3 & 56 & 6.80 & 8.17 + 25 & -5.8 & -15.2 & 40 & 0.92 & 1.10 + 26 & -6.5 & -4.4 & 56 & 7.15 & 8.58 + 27 & -7.3 & 3.6 & 40 & 3.02 & 3.62 + 28 & -8.0 & 4.4 & 56 & 3.86 & 4.63 + 29 & -9.4 & -5.1 & 97 & 17.00 & 20.40 + 30 & -10.2 & -4.4 & 112 & 19.20 & 23.00 + 31 & -10.9 & 1.5 & 56 & 1.64 & 1.97 + 32 & -12.3 & -1.5 & 40 & 1.91 & 2.29 + 33 & -13.1 & 0.0 & 79 & 7.53 & 9.04 + 34 & -14.5 & 4.4 & 97 & 5.58 & 6.70 + 35 & -14.5 & -2.2 & 56 & 6.92 & 8.30 + 36 & -16.0 & -13.1 & 97 & 5.73 & 6.88 + 37 & -18.1 & -8.7 & 56 & 1.30 & 1.56 + 38(c ) & -21.1 & 17.0 & 63 & 0.77 & 0.92 + 39 & -19.6 & -13.1 & 40 & 0.80 & 0.96 + a total of 39 hii regions were identified . they have been detected on the total h@xmath0 map and their presence on at least two consecutive channel maps has been carefully checked . a majority of them are well seen on fig.1 and 2 of ostlin et al . ( 1996 ) and also on fig . 1 of ht95 . observed hii regions are shown in the identification chart ( fig . 2 ) and listed in table 2 which gives the following informations : column 1 lists the reference number given to individual hii regions as shown in the chart . columns 2 and 3 give the x , y positions of the photometric center of the regions , in units of arcsec . the coordinate center is the h@xmath0 brightness peak in the nw component of the galaxy , positive values of @xmath10@xmath0 and @xmath10@xmath11 are to the east and north respectively . the faintest h@xmath0 fluxes correspond to a s / n threshold of 5 . columns 4 and 5 give the effective diameter @xmath17 of the regions in arcsec and parsecs . an equivalent diameter was defined in terms of the limiting isophotal area @xmath44 , of each hii region , according to the definition @xmath45 the limits of each region are defined by the contour where the intensity of the h@xmath0 emission falls down to the average local intensity of the diffuse background . columns 6 and 7 list the total dereddened h@xmath0 fluxes of the regions in units of 10@xmath46ergs @xmath27 and their h@xmath0 luminosities in units of 10@xmath47ergs @xmath1 . the faintest features listed in table 2 have an h@xmath0 flux corresponding to a minimum number of photons that gives a signal - to - noise of 5 . on fig . 2 is marked and listed in table 2 the zwicky s `` flare '' ( zwicky 1966 ) , component c by dh90 . about 1.5 arcsec displacement exists between its red ( table 1 ) and h@xmath0 ( table 2 ) peaks . this displacement also appears on fig . 2 of ostlin et al . ( 1996 ) . in fig . 4 we show the cumulative diameter distribution built according to table 2 . it is consistent with an exponential law @xmath48 = @xmath49exp(@xmath17/@xmath50 ) where @xmath50 = 24 pc . this value is comparable with @xmath50 values found for the irregular galaxies ( hodge 1983 ; hodge et al . 1989 ; hodge & lee 1990 ) . for izw18 the small number of hii regions prevents a derivation of an accurate luminosity function , but nevertheless the data are sufficient to get a first approximation . in fig . 5 the distribution of h@xmath0 luminosities binned in intervals of 1.0 10@xmath47ergs @xmath1 is presented . the observed luminosity function of izw18 shows a turnover with a maximum at @xmath51 = 3.0 10@xmath47ergs @xmath52 corresponding to the luminosity of the orion nebula ( gebel 1968 ) . this turnover is due to incompleteness towards fainter luminosities . at luminosities brighter than this turnoff the observed function is reasonably well fitted by a power law @xmath53=@xmath44@xmath54@xmath55 with a slope @xmath0 = -1.6@xmath560.3 . this is consistent with the mean value derived for dwarf irregular galaxies ( strobel et al . 1991 ) @xmath0 = - 1.5@xmath560.3 . it may be compared with the steeper slope @xmath0 = -1.7 found for larger irregulars by kennicutt et al . ( 1989 ) . figure 6 shows iso - velocity lines superimposed on the h@xmath0 gray scale image of izw18 . figure 7 is a position - velocity cut across the optical major axis of the galaxy across the nw and se compact components ( pa = 143@xmath57 ) . the shape of this position - velocity cut is in good agreement with slit 2 ( pa = 156.1@xmath57 ) position - velocity diagram of m96 . figures 6 and 7 show a clear overall regular radial velocity gradient across the main body of izw18 . this finding obtained from the ionized gas confirms an earlier result by viallefond et al . 1987 using hi aperture synthesis techniques . 7 further shows that the radial velocity gradient is globally consistent with a solid - body - like rotation of the ionized gas . the peaks of h@xmath0 emission in the nw and se components are respectively centered at 739 km @xmath1 and 779 km @xmath1 and their average velocities are equal to 742@xmath567 km @xmath1 and 783@xmath565 km @xmath1 . these values are in agreement with those obtained using high - resolution spectroscopy ( dkf89 ) . they are also very similar to the davidson & kinman ( 1985 ) and hi velocity results ( lequeux & viallefond 1980 ; viallefond et al . 1987 ) . the best symmetrical pattern of the velocity distribution is obtained along the major axis , when assuming a systemic recession velocity of 763 km @xmath1 . this value is in good agreement with the velocity of the number 5 hi cloud ( 765 km @xmath1 ) in lequeux & viallefond ( 1980 ) and relates to a region which is very close to the red continuum component ( a ) . assuming that the radial velocity gradient , ( which amounts to 73 km @xmath58 and is indicating a high mass concentration ) , is due to rotation ( m96 ) we derive a keplerian spherical mass of @xmath59 within a radius about 10 arcsec ( 480pc ) . within this radius , we derive @xmath60 for the mass of ionized gas . it corresponds to 1.6% of the total mass and about 40% of the neutral hi mass of the clump corresponding to the main body of izw18 ( lequeux & viallefond 1980 ; viallefond et al . 1987 ) . within this limited radius , such a simple approximation is sufficient to derive a realistic estimate of the total mass . any other more elaborate model will provide an estinate within a factor of 2 as compared to the keplerian spherical mass . over the regular velocity field of izw18 some complex structure is superimposed that locally modifies the isovelocity line and creates `` bumps '' at the position - velocity cut . these irregularities are particularly conspicuous in the nw region . across a 70x70 pc@xmath29 area located 150pc north from the peak intensity of the nw component we observe a local velocity excess of 15 - 17 km @xmath1 . the position of this excess coincides with the secondary peak in the spectrum of dfk89 . it is also coincident with the location of the red continuum ( b ) component ( fig . 1 , insert ) . this velocity structure has been previously discussed by m96 and by skillman & kennicutt ( 1993 ) . the latter authors suggest a merging of two ( or more ) clouds rather than a pure solid body rotation . we dispute this interpretation using our previous statements on the regularity of the general velocity pattern and further note that the violent star formation that occurs in the nw compact component is likely to induce local peculiar gas motions . other interesting velocity features relate to the ridge . in general the ridge follows the velocity distribution of the hi peak and izw18 velocity field . along the southern and part of the western length of the ridge , differences in radial velocities of the order of 10 - 15 km @xmath1 are found between its inner and outer regions . this difference is also evident across the slit 3 ( pa=78.8@xmath57 ) position - velocity diagram of m96 . no peculiar velocities were detected on the hii regions area of the ridge . coincident with zwicky s `` flare '' a small h@xmath0 knot has a radial velocity of about 730 km @xmath1 . therefore izw18 and the zwicky s `` flare '' belong to the same system . those hii regions detected in the main body of izw18 and its envelope ( sec.3.2 ) with sufficient s / n ratio exhibit radial velocities similar to that of the central velocity field . figure 8 and 9 display each individual h@xmath0 line profile superimposed to the h@xmath0 isophotal map of izw18 in order to show the line profile structure of the outer envelope and the h@xmath0 line intensity distribution across the galaxy . depending upon their location line profiles show different shapes . typical unsmoothed h@xmath0 line profiles are shown in fig . 10 together with the corresponding gaussian fits . in all cases , the observed broad wings have instrumental origin and are most probably caused by adjacent orders . table 3 reports the results of the line profile analysis conducted on areas where the signal - to noise ratio is sufficient to achieve gaussian or multi - gaussian fitting of the observed h@xmath0 line . @xmath61(main ) is the velocity dispersion of the main component of the line , corrected for thermal and instrumental broadening ( sec . 2 ) ; n(sec ) is the number of secondary gaussian profiles fitting the observed h@xmath0 line ; v(sec ) is the peak velocity difference between the main and secondary gaussian components ; i(sec)/i(main ) is the intensity ratio of the secondary and main gaussian components . the numbers in table 3 are average values taking into account several pixels for each region . cccccc & & nw region & se region & w ridge & s ridge + @xmath62 & & @xmath63 & 26.5@xmath560.4 & 16 & 16 + n(sec ) & & 0 & 1 & 2 & 2 + v(sec)(km s@xmath64 ) & @xmath65 & & -53.0@xmath562.7 & 45.3@xmath5611.9 & -40.7@xmath563.2 + & @xmath66 & & & -39.0@xmath567.0 & -76.8@xmath565.1 + i(sec)/i(main ) & @xmath65 & & 0.15 & 0.30 & 0.40 + & @xmath66 & & & 0.20 & 0.20 + the nw component h@xmath0 line profiles mainly appear symmetrical and well - represented by a one - component gaussian fit ( fig . it is interesting to note that in h@xmath0 line a small red asymmetry appears towards the direction of the se component . with the assumption that the component is a gravitationally bound system ( terlevich & melnick 1981 ) the total mass of the system is estimated about 2 10@xmath67@xmath38 and the fraction of ionized gas in it as about 3% . according to skillman & kennicutt ( 1993 ) a broad emission can be seen at the base of the h@xmath0 line profile for the nw component with a peak amplitude at about 0.2% of the main h@xmath0 line and a fwhm of about 80 ( about 3600 km @xmath1 ) . the small free spectral range ( 375 km @xmath1 ) of the fabry - perot interferometer prevents to detect this broad component . all h@xmath0 line profiles observed in pixels belonging to the se component are asymmetric with blue side excesses ( fig . this blueshifted component contributes in average to 13% of the line flux and has a mean velocity of -50 km @xmath1 from the systemic velocity of the main component . again , the small free spectral range of our observations ( 375 km @xmath1 ) forbids the detection of faint large velocity components such as the ones found by m96 with velocities up to 230 km @xmath1 and a an intensity of about 3% of the main line flux . across the western part of the ridge ( fig . 10c ) profiles with blue and red velocities excesses are typical . usually redshifted components are more intense than blueshifted ones . across the southern part of the ridge profiles with strong blue side asymmetry are typical ( fig . two secondary components with 25% and 12% contributions of the line flux and -41 km @xmath1 and -77 km @xmath1 blueshifted from the systemic velocity of the main component were discovered . the bright knot well seen on the m96 echelle spectrum at h@xmath0 along the slit position 1 ( pa=7.7@xmath57 ) ( see her fig . 2 ) is caused by the southern part of the ridge . the two blueshifted components in the h@xmath0 profiles of the ridge are well separated in velocity ( see fig . this is well in agreement with the velocity range displayed in the m96 spectrum observed across the ridge position . on the so called sw doppler ellipse ( m96 ) , nearly 4south from the ridge position , another fainter knot is observed that refers to our hii region number 23 . in the outer enveloppe of the main body of the galaxy , profiles are mainly asymmetric with red wings in the north - west and west of the se component ( m96 ) , and with blue wings elsewere . in the ne doppler ellipse of m96 ( her fig . 2 ) , three other hii regions from our list have been identified as they appear as individual knots : number 9 and number 10 merged with number 12 . all three hii regions have h@xmath0 line profiles with blueshifted components .

we present high spatial resolution observations of the blue compact dwarf galaxy izw18 performed in the h line with a scanning fabry - perot interferometer at the cfh telescope . morphological structure of the galaxy in h and in the red continuum is investigated . they have no clear h counterparts . the velocity field in izw18

we present high spatial resolution observations of the blue compact dwarf galaxy izw18 performed in the h line with a scanning fabry - perot interferometer at the cfh telescope . morphological structure of the galaxy in h and in the red continuum is investigated . we also analyse the velocity field of the ionized gas . besides the two compact hii components of the main body we find a population of small hii regions in its surroundings whose diameter distribution and h luminosity function are consistent with those observed in dwarf irregular galaxies . in the main body of the galaxy besides of the nw and se red continuum peaks which are displaced with respect to the h maxima , three new red condensations have been discovered . they have no clear h counterparts . the velocity field in izw18 shows peculiar motions superimposed on a quite regular background implying solid - body rotation with a gradient of about 70 km kpc . the h line profiles exhibit an asymmetric structure , except for the nw main compact component . at least part of this asymmetry could result from accreted and/or expelled surrounding gas from the main star - forming core(s ) of the galaxy . contrary to previous suggestions that the south - west and north - east extensions of this galaxy are diffused emission produced by bipolar emitting gas we provide evidence that they are hii regions powered by star formation sites . the redshift of the zwicky s `` flare '' has been measured for the first time and corresponds to the same velocity as izw18 . in such a context the optical ridge that appears to be an isolated morphological structure has a shape that may result from the gravitational interaction with the zwicky s `` flare '' if this latter is a neighbour extreme dwarf object .

astro-ph9612079

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the main results of h@xmath0 scanning fabry - perot investigations of izw18 may be summarized as follows : + - in the main body of this galaxy , the _ current _ sites of active star formation , identified from the presence of prominent emission lines have ages of few 10@xmath70 years and are spatially separated from red continuum clumps which are sites of recent star formation episodes with ages of about few tenth of 10@xmath70 years . all star formation sites in the galaxy are separated from the compact hi cloud double - peaked core . - the h@xmath0 line profiles have a complex structure , and except in the nw hii compact region , can not be fitted by single gaussian components . the presence of blue and/or red wings in many points of the envelope suggests a generalized pattern of infalling ( expelling ) gas clouds onto ( from ) the central star forming regions . - the observed `` ridge '' is an isolated morphological structure in the system . it is a star forming site separated with respect to the izw18 main body by the hi cloud . the shape and orientation of this ridge can be due to tidal interation between izw18 and the zwicky s `` flare '' . - the sw and ne extensions of the outer envelope of the galaxy besides the ionized gas component connected to a supergiant shell - expanding superbubble ( m96 ) also contain stellar as well as hii regions components . - the near environment of the galaxy is likely to be polluted not only with gas processed by the central massive stars and driven out by superwinds but also by products of a more local stellar population . when compared to the average characteristics of dwarf irregular galaxies , the basic properties of izw18 ( luminosity , hi mass , solid body rotation , normal hii region population , existence of current and recent star formation sites ) are consistent with the hypothesis of an overall similarity between this blue compact dwarf galaxy and a typical dwarf irregular . the rigid - body rotational velocity gradient and the blue surface brightness , which depend on the linear scale are much larger in izw18 . the essential difference is that a high star formation activity ( an order of two magnitudes in the sf rate per unit area which respect to that observed in a typical dwarf irregular ) is concentrated in a small compact region . @xmath86 we would like to thank dr . deidre hunter for providing her hst - wfpc2 data for izw18 and dr . miguel mas - hesse for his model calculations of stellar contribution at 6600 with respect to the nebular continuum . part of this research was supported by pics ( programme international de cooperation scientifique ) # 247 of cnrs between france and armenia . the financial support of international association for the promotion of cooperation with scientists from the independant states ( intas ) is gratefully acknowledged . petrosian would like to thank the warm hospitality of institut dastrophysique de paris and observatoire de marseille during his stay . we also thank jean mouette for his help during the preparation of the figures . allsopp , n.j . 1978 , mn , 184 , 397 arnault , p. , casoli , f. , combes , f. , kunth , d. 1988 , a&a , 205 , 41 arsenault , r. , roy , j .- 1986 , aj , 92 , 567 arsenault , r. , roy , j .- 1988 , a&a , 201 , 199 bertola , f. , casini , c. , bettoni , d. , galletta , g. , noreau , l. , kronberg , p.p . 1984 , aj , 89 , 350 boulesteix , j. , georgelin , y.p . , marcelin , m. , monnet , g. 1983 , spie conf . astron . , 5 , 445 , 37 copetti , m.v.f . , pastoriza , m.g . , dottori , h.a . 1985 , a&a , 152 , 427 davidson , k. , kinman , t.d . 1985 , apjs , 58 , 321 davidson , k. , kinman , t.d . , friedman , s.d . 1989 , aj , 97 , 1591 ( dfk89 ) dopita , m.a . 1972 , a&a , 17 , 165 dufour , r.j . 1986 , pasp , 98 , 1025 dufour , r.j . hester j.j . , 1990 , apj , 350 , 149 ( dh90 ) dufour , r.j . garnett d.r . , shields g.a . , 1988 , apj , 332 , 752 gallagher , iii j.s . , hunter , d.a . 1983 , apj , 274 , 141 gallagher , iii j.s . , hunter , d.a . 1984 , ara&a , 22 , 37 gebel , w.c . 1968 , apj , 153 , 743 gerola , h. , seiden , p.e . , schulman , l.s . 1980 , apj , 242 , 517 filippenko , a.v . 1982 , pasp , 94 , 715 hippelein , h. , fried , j.w . 1984 , a&a , 141 , 49 hodge , p.w . 1983 , aj , 88 , 1323 hodge , p.w . , lee , m.g . 1990 , pasp , 102 , 26 hodge , p.w . , lee , m.g . , kennicutt , jr . 1989,pasp , 101 , 32 hopp , u. , schulte - ladbeck , r.e . 1991 , a&a , 248 , 1 hua , c.t . , grundseth , b. , nguyen - trong , t. 1987 , ap let . comm . , 25 , 187 huchra , j.p . 1977 , apjs , 35 , 171 hunter , d. a. 1982 , apj , 260 , 81 hunter , d.a . , gallagher , iii j.s . 1985 , apjs , 58 , 533 hunter , d.a . , gallagher , iii j.s . 1986 , pasp , 98 , 5 hunter , d.a . , thronson , jr . h.a . 1995 , apj , 452 , 238 ( ht95 ) kennicutt , jr . r.c . , edgar , b.k . , hodge , p.w . 1989 , apj , 337 , 761 klein , u. , grave , r. , wielebinski , r. 1983 , a&a , 117 , 332 kunth , d. , sevre , f. 1986 , star forming dwarf galaxies , eds . d.kunth , t.x.thuan , j.t.t.van , ( editions frontieres ) p.331 kunth , d. , sargent , w.l.w . 1986 , apj . , 300 , 496 kunth , d. , maurogordato , s. , vigroux , l. 1988 , a&a , 204 , 10 kunth , d. , lequeux , j. , sargent , w.l.w , viallefond , f. 1994 , a&a , 282 , 709 kunth , d. , matteucci , f. , marconi , g. 1995 , a&a , 297 , 634 laval , a. , boulesteix , j. , georgelin , y.p . , georgelin , y.m . , marcelin , m. 1987 , a&a . , 175 , 199 lequeux , j. , viallefond , f. 1980 , a&a , 91 , 269 lequeux , j. , peimbert , m. , rayo , j.f . , serrano , a. , torres- peimbert , s. 1979 , a&a , 80 , 155 lequeux , j. , maucherat - joubert , m. , deharveng , j.m . , kunth , d. 1981 , a&a , 103 , 305 lequeux , j. , kunth , d. , mas - hesse , j.m . , sargent , w.l.w . 1995 , a&a , 301 , 18 loose , h .- h . , thuan , t.x . 1986 , star forming dwarf galaxies , eds . d. kunth , t.x.thuan , j.t.t.van , ( editions frontieres ) , p. 73 martin , c. 1996 , apj , in press ( m96 ) mazzarella , j.m . , boroson , t.a . 1993 , apjs , 85 , 27 mazzarella , j.m . , bothun , g.d . , boroson , t.a . 1991 , aj , 101 , 2034 melnick , j. , terlevich , r. , moles , m. 1988 , mn , 235 , 297 ostlin , g. , bergvall , n. , ronnback , j. 1996 , in `` the interplay between massive star formation , the ism and galaxy evolution '' , ed.kunth d. , guiderdoni b.,heydari - malayeri t.x . thuan , ( editions frontieres ) , in press osterbrock , d.e . 1989 , astrophysics of gaseous nebulae and active galactic nuclei ( university science books : mill valley , ca ) pettini , m. , lipman , k. 1995 , a&a , 297 , l63 petrosian , a.r . , saakian , k.a . , khachikian , e.e . 1978 , afz , 14 , 69 rosa , m. , solf , j. 1984 , a&a , 130 , 29 roy , j .- r . , boulesteix , j. , joncas , g. , grundseth , b. 1991 , apj , 367 , 141 roy , j .- r . , aube , m. , mccall , m.l . , dufour , r.d . 1992 , apj , 386 , 498 saito , m. , sasaki , m. , ohta , k. , yamada , t. 1992 , pasj , 44 , 593 sargent , w.l.w . , searle , l. 1970 , apj , 162 , l155 searle , l. , sargent , w.l.w . 1972 , apj , 173 , 25 shostak , g.s . , skillman , e.d . 1989 , a&a , 214 , 33 skillman , e.d . , kennicutt , jr.r.c . 1993 , apj , 411 , 655 strobel , n.v . , hodge , p. , kennicutt , jr.r.c . 1991 , apj , 383 , 148 taylor , c.l . , skillman , e.d . , brinks , e. 1991 , baas , 23 , 920 terlevich , r. , melnick , j. 1981 , mn , 195 , 839 thuan , t.x . 1983 , apj , 268 , 667 thuan , t.x . 1987 , starbursts and galaxy evolution , eds . , t.montmerle , t.x.thuan , j.t.t.van , ( edition frontieres ) , p.129 thuan , t.x . , williams , t.b . , malumuth , e. 1987 , star bursts and galaxy evolution , eds.,t.montmerle , t.x.thuan , t.t.van,(editions frontieres ) , p.151 tomita , a. , ohta , k. , saito , m. 1993 , pasj , 45 , 693 tremaine , s. , gunn , j.e . 1979 , phys . rev.letters , 42 , 407 viallefond , f. , thuan , t.x . 1983 , apj , 269 , 444 viallefond , f. , lequeux , j. , comte , g. 1987 , star bursts and galaxy evolution , eds . t. montmerle , t.x . thuan , t .- t.van , ( editions frontieres ) , p.139 vigroux , l. , stasinska , g. , comte , g. 1986 , star forming dwarf galaxies , eds d. kunth , t.x . thuan , j.t.t . van , editions frontieres , p. 425 zwicky , f. 1966 , apj , 143 , 166

we also analyse the velocity field of the ionized gas . besides the two compact hii components of the main body we find a population of small hii regions in its surroundings whose diameter distribution and h luminosity function are consistent with those observed in dwarf irregular galaxies . in the main body of the galaxy besides of the nw and se red continuum peaks which are displaced with respect to the h maxima , three new red condensations have been discovered . the h line profiles exhibit an asymmetric structure , except for the nw main compact component . contrary to previous suggestions that the south - west and north - east extensions of this galaxy are diffused emission produced by bipolar emitting gas we provide evidence that they are hii regions powered by star formation sites . the redshift of the zwicky s `` flare '' has been measured for the first time and corresponds to the same velocity as izw18 . in such a context the optical ridge that appears to be an isolated morphological structure has a shape that may result from the gravitational interaction with the zwicky s `` flare '' if this latter is a neighbour extreme dwarf object .

we present high spatial resolution observations of the blue compact dwarf galaxy izw18 performed in the h line with a scanning fabry - perot interferometer at the cfh telescope . morphological structure of the galaxy in h and in the red continuum is investigated . we also analyse the velocity field of the ionized gas . besides the two compact hii components of the main body we find a population of small hii regions in its surroundings whose diameter distribution and h luminosity function are consistent with those observed in dwarf irregular galaxies . in the main body of the galaxy besides of the nw and se red continuum peaks which are displaced with respect to the h maxima , three new red condensations have been discovered . they have no clear h counterparts . the velocity field in izw18 shows peculiar motions superimposed on a quite regular background implying solid - body rotation with a gradient of about 70 km kpc . the h line profiles exhibit an asymmetric structure , except for the nw main compact component . at least part of this asymmetry could result from accreted and/or expelled surrounding gas from the main star - forming core(s ) of the galaxy . contrary to previous suggestions that the south - west and north - east extensions of this galaxy are diffused emission produced by bipolar emitting gas we provide evidence that they are hii regions powered by star formation sites . the redshift of the zwicky s `` flare '' has been measured for the first time and corresponds to the same velocity as izw18 . in such a context the optical ridge that appears to be an isolated morphological structure has a shape that may result from the gravitational interaction with the zwicky s `` flare '' if this latter is a neighbour extreme dwarf object .

astro-ph0411026

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in this paper we have presented detailed multicolor surface photometry performed with a ccd in the @xmath100 bands and a nicmos detector in the @xmath1 band , for a sample of 34 lenticular galaxies from the ugc catalogue . the galaxies were chosen in an unbiased fashion from a subset of ugc lenticulars as explained in section 2 . we have obtained total integrated magnitudes and colors for all the galaxies using elliptical annuli from surface photometry , and find that these are in good agreement with values from the rc3 catalogue . using isophotal analysis we have obtained radial profiles of the surface brightness , ellipticity , position angle , and higher order fourier coefficients in all the bands . the profiles in the different bands are consistent with each other , and any differences can be attributed to the presence of dust and other features which produce wavelength dependent effects . we have used the surface brightness profiles to obtain color profiles , and logarithmic color gradients , and find that the gradients are negative , indicating that the colors of lenticulars become redder towards the center , as is the case with elliptical galaxies . we have shown that there is good correlation between @xmath2 and @xmath3 color gradients for lenticulars . numerical profiles of all parameters that we have obtained from the isophotal analysis along with the color images are available at _ http://www.iucaa.ernet.in/@xmath79sudhan / s0.html_. our intention in obtaining the multiband data on lenticulars has been to study in detail these galaxies as a class , and to compare their properties with those of ellipticals and early type spirals . an important aspect of this study will be the decomposition of the lenticulars into bulge and disk components and the comparison of these separately with the bulges and disks in other types of galaxies where these components occur with varying degrees of prominence . we will use the results of the decomposition in a multiband study of the fundamental and photometric planes for lenticulars . we will also make a detailed study of the distribution of dust in lenticulars , particularly in those galaxies from our sample where there are prominent dust features and where we have multiband data at optical as well as near - infrared wavelengths . the staff at oagh and spm are greatfully acknowledged for their help during the observations . sb and skp thank iucaa for hospitality and the use of facilities without which this work could not have been done and for providing funds for observations . akk and sb thank inaoe for hospitality provided during there visits . we also thank the anonymous referee for several useful comments , which helped to improve the original manuscript . this research has made use of the nasa / ipac extragalactic database ( ned ) , which is operated by the jet propulsion laboratory , california institute of technology , under contract with the national aeronautics and space administration . in this appendix , we discuss structural properties of each galaxy , whenever isophotes in one or more bands depart from a smooth ellipse . the discussions are focused on any disagreement in the morphological classification in ugc and rc3 catalogs , presence of dust lane , change of ellipse - fit parameters ( b4 , pa or ellipticity ) , existence of any ring , and any evidence of nuclear activity . published information on any of these issues , if available , is noted . in total 12 galaxies ( ugc926 , 1823 , 3452 , 3567 , 3683 , 3699 , 3824 , 6013 , 6389 , 6899 , 11972 and 12443 ) are smooth lenticular galaxies without any identifiable feature in the direct images , the surface brightness profiles , color or extinction maps . comments for the remaining galaxies follow . * ugc80 :* ugc80 is a barred lenticular galaxy , having a very faint interacting companion . the faint bar is almost perpendicular to the galaxy major axis , and is clearly evident in the isophotal profile . the @xmath101 profile is indicative of a disky shape over the entire major - axis range explored . the ellipticity and position angle profiles show abrupt change at @xmath102 , where there is also a kink in the brightness profile . the @xmath3 color map of the galaxy shows a red feature near the center . * ugc491 :* ugc491 is the brightest galaxy in a small group with ngc0258 and ngc0260 . this galaxy is classified as s0 in the ugc catalogue and sa(r ) in the rc3 catalogue . in the optical images it indeed shows a ring , which is also evident in the @xmath3 and @xmath103 color maps . ellipticity and position angle profiles show a change at @xmath104 , which may be due to the presence of the ring . * ugc859 :* ugc859 shows an internal ring , but it is classified as s0 in the ugc catalogue . the @xmath3 and @xmath103 color maps of the galaxy show the ring as an inhomogeneous structure . a low surface brightness disk with some luminous spiral structure exists outside the ring . ugc 859 has been detected by iras and has flux densities of @xmath105 at @xmath106 and @xmath107 at @xmath108 ( knapp 1989 ) . the @xmath101 coefficient is disky towards the outer region . * ugc1250 :* while this galaxy is classified as s0 , the @xmath3 color map of the galaxy show a very clear , but distorted ring , just around the bulge . @xmath109 $ ] observations by pogge & eskridge ( 1993 ) show copious hii regions across the disk . the @xmath101 profile is disky at all major - axis lengths , with the coefficient being larger in the inner region of the galaxy . * ugc2039 :* ugc2039 is paired with ugc 2049 . there is a rise in the ellipticity from 0.1 to 0.5 towards the outer region . the @xmath101 coefficient is disky in the outer region , which suggests the presence of a significant disk . the galaxy has been detected by iras at 60 and @xmath108 . * ugc3087 :* previous studies of ugc3087 have mainly concentrated on its nuclear activity . it is a strong radio source ( 3c120 ) and the optical spectrum suggests a seyfert 1 nucleus ( tadhunter 1993 ) . it has a faint optical jet in the same apparent direction as the radio jet . the optical jet is clearly visible in our images and distorts isophotal profiles in the inner region . * ugc3178 :* a dust feature is clearly visible in the @xmath55 band extinction map of this galaxy , and is also detectable from the isophotal analysis of @xmath55 and @xmath1 band images . the @xmath101 coefficient , position angle and ellipticity are different in @xmath55 and @xmath1 , which may be due to dust absorption in @xmath55 . our @xmath57 and @xmath26 band images suffer from poor s / n . * ugc3536 :* this galaxy has a significant dusty disk and the @xmath101 coefficient is disky . the disk is also evident in the @xmath2 and @xmath3 color maps . there is a constant rise in ellipticity for semi - major axis length @xmath110 , beyond which there is a decrease , which could be because of the disk . * ugc3792 :* this galaxy is classified as s0 in the ugc but as sa0/a in the rc3 catalogue , and has no previous reported photometric study . the galaxy has a prominent dust lane along the major axis which greatly affects the various profiles . this dust lane is most prominent in the @xmath55 band . the @xmath101 coefficient is positive in the outer region . there is a large color gradient in @xmath75 and @xmath5 , presumably because of the dust . a detailed study of this galaxy in the @xmath111 bands will be presented in a forthcoming paper . * ugc4347 :* our @xmath2 and @xmath103 color and extinction maps of this galaxy reveal a large dust patch near the center . the @xmath101 profile is disky throughout the observed region . forbes & thomson ( 1992 ) have detected possible shells in this galaxy . the extinction images in all bands shows faint structures , which may be responsible for the non - zero values the of @xmath101 coefficient . * ugc4767 :* the position angle and ellipticity profile for this galaxy are different in the @xmath112 and @xmath1 bands for semi - major axis lengths @xmath113 , which could be because of a dust patch near the center of the galaxy . the various color maps also indicate the presence of the dust patch . * ugc4901 :* our @xmath55 band image of this galaxy has poor s / n . the color maps in @xmath114 and @xmath5 show no features in the galaxy . the @xmath101 coefficient is positive towards the outer region , suggesting the presence of a faint disk . * ugc7473 :* this well studied edge - on lenticular galaxy forms a pair with ngc 4340 . the surface brightness profile of this galaxy clearly indicates the presence of bulge and disk components . the mg@xmath115 line strength profiles along the major and minor axis of the galaxy differ dramatically and convincingly indicate the presence bulge and disk components ( fisher , franx & illingworth 1996 ) . michard & marchal ( 1993 ) described ugc7473 as having a disk fully embedded in a spheroidal halo . a disk of rapidly rotating gas is present within the inner @xmath116 ; this is decoupled from the stellar component ( fisher 1997 ) . a concentration of dust in the disk has been proposed by michard & poulain ( 2000 ) . our @xmath3 and @xmath103 color and extinction maps also reveal a clear inclined disk . the ellipticity rises from 0.2 to 0.61 over the observed region and the @xmath101 coefficient becomes significantly positive beyond @xmath117 , which reflects the presence of a strong disk . * ugc7880 :* this galaxy forms a pair with ngc 4635 , with a separation of at @xmath118 . the ellipticity changes from 0.1 to 0.5 upto @xmath119 , and decreases beyond that . the @xmath101 coefficient is positive upto the point at which the ellipticity begins to decrease . this may be due to the presence of an inner disk , the presence of which is also indicated by the @xmath3 and @xmath103 color and extinction maps . * ugc7933 :* this galaxy is classified as s0 in the ugc , but as e1 - 2 in the rc3 catalogue . it forms a non - interacting pair with ngc4670 at @xmath120 separation . the @xmath55 band image has poor s / n . the @xmath101 coefficient is positive towards the outer region . the color and extinction maps do not indicate any structure . * ugc8675 :* this is a little studied s0 galaxy hosting a seyfert 1.5 nucleus , and has been classified as a sa0 galaxy in the rc3 catalogue . the isophotes of the galaxy are nearly circular and at @xmath121 the ellipticity becomes 0.15 which is consistent with the values obtained by de robertis , hayhoe & yee ( 1998 ) and pierre ( 2000 ) . a dust absorption pattern is seen near the nucleus in the @xmath3 and @xmath103 color and extinction maps . pierre ( 2000 ) have found from hst observations a u - shaped dust lane circling around the nucleus . * ugc11178 :* this galaxy has no previous reported photometric study . the extinction map show a ring like structure in all the bands . the ellipticity abruptly changes between 5 and @xmath122 , which could be because of the ring like structure . the @xmath101 coefficient is significantly positive upto @xmath122 . the color maps are featureless . * ugc11781 :* this galaxy is classified as s0 in the ugc but as sab in the rc3 catalogue . the presence of a bar is clear in the direct as well as extinction images . there is a dip in ellipticity profile at @xmath119 , where there is a change in the position angle profile as well . the @xmath101 coefficient is positive in this region .

we present in this paper multicolor surface and aperture photometry in the and bands for a sample of 34 lenticular galaxies from the ugc catalogue . from surface photometric analysis we obtain total integrated magnitudes and colors and find that these are in good agreement with the values from the rc3 catalogue .

we present in this paper multicolor surface and aperture photometry in the and bands for a sample of 34 lenticular galaxies from the ugc catalogue . from surface photometric analysis , we obtain radial profiles of surface brightness , colors , ellipticity , position angle and the fourier coefficients which describe the departure of isophotal shapes from purely elliptical form and find the presence of dust lanes , patches and ring like structure in several galaxies in the sample . we obtain total integrated magnitudes and colors and find that these are in good agreement with the values from the rc3 catalogue . isophotal colors are correlated with each other , following the sequence expected for early - type galaxies . the color gradients in lenticulars are more negative than the corresponding gradients in ellipticals . there is a good correlation between and color gradients , and the mean gradient in the and colors are , , magnitude per dex in radius respectively .

1703.03526

i

high - redshift ( z @xmath4 5 ) quasars are important tracers to study the early universe . however , they are difficult to be found due to both low spatial density and high contaminants from cool dwarfs when using color selection . although more than 300,000 quasars are now known ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , only @xmath3 290 quasars are at @xmath5 5 . in the distribution of quasar redshift , there is an obvious gap of known quasars at 5.3 @xmath6 5.7 , due to their similar optical colors to that of late - type stars ( see the redshift distribution in sec . 4 ) . only @xmath3 30 known quasars have been found in this redshift gap over a wide magnitude range ( 17.5 @xmath6 26 mag ) ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? compared to the studies at lower redshift and higher redshift , this gap posts significant limit on the study of quasar evolution from @xmath1 5 to 6 , over the post - reionization epoch . observations of the gunn - peterson effect using absorption spectra of high redshift quasars suggest that reionization is just completing at @xmath7 6 , possibly with a tail to @xmath7 5.5 @xcite . therefore , the physical conditions of the post reionization igm , at @xmath1 5 - 6 , provides the basic boundary conditions of models of reionization , such as the evolution of igm temperature , photon mean free path , metallicity and the impact of helium reionization ( e.g. * ? ? ? they place strong constraints on reionization topology as well as on the sources of reionization and chemical feedback by early galaxy population . ly@xmath8 opacity measurement directly probes the evolution of igm . following @xcite , several new measurements about the ly@xmath8 opacity at 5 @xmath6 6 are given @xcite , but igm statistics are still poorly constrained at @xmath9 @xcite . moreover , a quasar sample in this redshift range is also a key to study the evolution of quasar luminosity function ( qlf ) and black hole growth . at high redshift , the qlf and black hole evolution have been measured at @xmath1 5 and 6 @xcite . however , at @xmath1 5.5 they are still poorly measured due to the lack of a complete quasar sample . @xcite derived the quasar spatial density at @xmath1 4 , 4.9 and 6 , and fitted a luminosity - dependent density evolution model to the combined dataset . they concluded that the quasar number density evolution steepens at high redshift , such that luminous quasars decline as a population more steeply at @xmath5 5 than from @xmath10 4 to @xmath10 5 ( also * ? ? ? however , the exact evolution of quasar density from @xmath11 = 5 to 6 is unclear because of the small size and high incompleteness of existing @xmath1 5.5 quasar sample . the quasar number density at @xmath12 is also needed to estimate the contribution of quasars to the ionizing background just after the reionization epoch . @xcite suggested that there was a rapid black hole mass growth phase after @xmath1 6 . study of black hole growth at @xmath1 4.8 supports that the notion of fast smbh growth at this epoch , corresponding to probably the first such phase for most smbh @xcite . studying bh growth properties at @xmath0 will fill in the missing link between @xmath13 and 6 . to answer the questions posted above , a large , uniformly selected sample of quasars at @xmath14 is needed . however , so far there has not ever been a complete quasar survey at @xmath0 . as shown in 2 , broad - band colors of @xmath0 quasars are very similar to those of much more numerous m dwarfs , when a small number of passbands are used . therefore , to avoid the lager number of star contaminations , previous quasar selections have always excluded the region of m dwarf locus in @xmath15 color - color diagram . as a result , most surveys of high - redshift quasars have avoided the color space occupied by @xmath12 quasars and are highly incomplete at this redshift . to construct a large uniform @xmath1 5.5 quasar sample , a more effective selection to separate quasars from m dwarf in this most contaminated region is required . in this paper , we report initial results from a new search that focuses on the selection of @xmath0 quasars . our new color selection criteria based on optical , near- and mid - ir colors have yielded 17 quasars in the redshift range of 5.3 @xmath2 5.7 during the pilot observation described here . our optical / ir color selection technique and candidate selection using a combination of existing and new imaging surveys are described in section 2 . the details of our spectroscopy observations and new discoveries are presented in section 3 and section 4 . in section 5 , we discuss the completeness of our new selection and also report a test selection and first discovery using the preliminary version of the ukirt hemisphere survey ( uhs ) photometric data . a summary is given in section 6 . in this paper , we adopt a @xmath16cdm cosmology with parameters @xmath17 = 0.728 , @xmath18 = 0.272 , @xmath19 = 0.0456 , and h@xmath20 = 70 @xmath21 @xcite . photometric data from the sloan digital sky survey ( sdss ) are in the sdss photometric system @xcite , which is almost identical to the ab system at bright magnitudes ; photometric data from ir surveys are in the vega system . all sdss data shown in this paper are corrected for galactic extinction .

we present initial results from the first systematic survey of luminous quasars . quasars at 5.5 , the post - reionization epoch , are crucial tools to explore the evolution of intergalactic medium , quasar evolution and the early super - massive black hole growth . however , it has been very challenging to select quasars at redshifts 5.3 5.7 using conventional color selections , due to their similar optical colors to late - type stars , especially m dwarfs , resulting in a glaring redshift gap in quasar redshift distributions . including other two 5.5 quasars already published in our previous work , we now construct an uniform quasar sample at 5.3 5.7 with 17 quasars in a 4800 square degree survey area . for further application in a larger survey area , we apply our selection pipeline to do a test selection by using the new wide field j band photometric data from a preliminary version of the ukirt hemisphere survey ( uhs ) .

we present initial results from the first systematic survey of luminous quasars . quasars at 5.5 , the post - reionization epoch , are crucial tools to explore the evolution of intergalactic medium , quasar evolution and the early super - massive black hole growth . however , it has been very challenging to select quasars at redshifts 5.3 5.7 using conventional color selections , due to their similar optical colors to late - type stars , especially m dwarfs , resulting in a glaring redshift gap in quasar redshift distributions . we develop a new selection technique for 5.5 quasars based on optical , near - ir and mid - ir photometric data from sloan digital sky survey ( sdss ) , ukirt infrared deep sky surveys - large area survey ( ulas ) , vista hemisphere survey ( vhs ) and wide field infrared survey explorer ( wise ) . from our pilot observations in sdss - ulas / vhs area , we have discovered 15 new quasars at 5.3 5.7 and 6 new lower redshift quasars , with sdss z band magnitude brighter than 20.5 . including other two 5.5 quasars already published in our previous work , we now construct an uniform quasar sample at 5.3 5.7 with 17 quasars in a 4800 square degree survey area . for further application in a larger survey area , we apply our selection pipeline to do a test selection by using the new wide field j band photometric data from a preliminary version of the ukirt hemisphere survey ( uhs ) . we successfully discover the first uhs selected 5.5 quasar .

0801.4578

i

mid - infrared spectroscopy is a useful tool in investigating the extent to which starbursts and agn contribute to the luminosity of luminous infrared galaxies ( lirgs ; @xcite ) . the infrared spectra of local lirgs have been studied extensively with isophot , isocam and sws on the @xmath9 @xmath10 @xmath11 ( iso ; e.g. , @xcite ; @xcite ; @xcite ; @xcite ) and more recently with the infrared spectrograph ( irs ; @xcite ) on the @xmath12 ( @xcite ; @xcite ; @xcite ; @xcite ) . @xmath1 irs has also extended these studies to fainter sources at higher redshifts . a particularly interesting population of high redshift optically faint infrared luminous sources ( @xcite ; @xcite ; @xcite ; @xcite ) has been discovered using the multiband imaging photometer ( mips ; @xcite ) . various observing programs with @xmath1 irs have found that mips sources at flux density levels of f@xmath13(24@xmath3 ) @xmath14 0.8 mjy with optical magnitudes @xmath15 @xmath16 24 are typically at z @xmath17 2@xmath73 ( @xcite ; @xcite @xcite ; @xcite ) . the infrared spectra exhibit a wide range of properties from deep 9.7@xmath3 silicate absorption features and/or strong polycyclic aromatic hydrocarbon ( pah ) emission features to featureless power - law continua . this obscured population is important in determining how much light originates from starbursts and agn at epochs in the universe when their luminosity density was at its maximum . given that their optical faintness makes optical follow - up difficult , understanding how to characterize these sources using their infrared spectra is important in understanding their energetics . one approach in understanding the contribution of starbursts and agn to the infrared emission of optically faint infrared sources is to investigate the infrared spectra of sources also selected in other wavebands . for example , at one extreme we can study sources selected on the basis of large far - infrared flux densities , which we might expect to contain cool dust and show signatures of starbursts . in @xcite , we presented the irs spectra of 11 70@xmath3-selected optically faint infrared luminous galaxies and found that seven had large 6.2@xmath3 pah equivalent widths , consistent with them being powerful starburst galaxies . four of the galaxies showed deep silicate absorption features and their properties suggested that agn are likely to be the dominant origin of their large mid - infrared luminosities . at the other extreme , we can consider sources selected on the basis of x - ray flux , which we might expect to show spectral signatures of agn . @xcite presented irs spectra of 9 x - ray - loud optically faint infrared luminous galaxies selected from the @xmath1 wide - area infrared extragalactic survey ( swire ; @xcite ) . eight sources have silicate absorption features and one source has a featureless power - law mid - ir spectrum . in this paper , we present @xmath1 irs spectra of 16 optically faint infrared galaxies in the botes field of the noao deep wide - field survey ( ndwfs ; @xcite ) which are selected to be x - ray loud . this significantly increases the number of x - ray loud optically faint infrared luminous galaxies thus far studied , and extends the sample to higher x - ray and 24@xmath3 luminosities . a cosmology of @xmath18 , @xmath19=0.3 , and @xmath20=0.7 is assumed throughout .

we present mid - infrared spectroscopy of a sample of 16 optically faint infrared luminous galaxies obtained with the infrared spectrograph ( irs ) on the . these sources were jointly selected from and imaging surveys in the ndwfs botes field and were selected from their bright x - ray fluxes to host luminous agn . none of the spectra show significant emission from polycyclic aromatic hydrocarbons ( pahs ; 6.2 equivalent widths.2 ) , consistent with their infrared emission being dominated by agn . the average silicate absorption strength is not as strong as that of previously targeted optically faint infrared luminous galaxies with similar mid - infrared luminosities implying that the x - ray selection favors sources behind a smaller column of si - rich dust than non - x - ray selection . seven of the x - ray sources have featureless power - law mid - ir spectra .

we present mid - infrared spectroscopy of a sample of 16 optically faint infrared luminous galaxies obtained with the infrared spectrograph ( irs ) on the . these sources were jointly selected from and imaging surveys in the ndwfs botes field and were selected from their bright x - ray fluxes to host luminous agn . none of the spectra show significant emission from polycyclic aromatic hydrocarbons ( pahs ; 6.2 equivalent widths.2 ) , consistent with their infrared emission being dominated by agn . nine of the x - ray sources show 9.7 silicate absorption features . their redshifts are in the range , implying infrared luminosities of log(l)=12.5.6 . the average silicate absorption strength is not as strong as that of previously targeted optically faint infrared luminous galaxies with similar mid - infrared luminosities implying that the x - ray selection favors sources behind a smaller column of si - rich dust than non - x - ray selection . seven of the x - ray sources have featureless power - law mid - ir spectra . we argue that the featureless spectra likely result from the sources having weak or absent silicate and pah features rather than the sources lying at higher redshifts where these features are shifted out of the irs spectral window . we investigate whether there are any correlations between x - ray and infrared properties and find that sources with silicate absorption features tend to have fainter x - ray fluxes and harder x - ray spectra , indicating a weak relation between the amount of silicate absorption and column density of x - ray - absorbing gas .

0801.4578

r

the irs spectra of all 16 x - ray selected sources are shown in figure [ fig : xspec ] . although the irs spectrum of houck13 was presented in @xcite , it satisfies the selection criteria of the main sample and we include it again here for completeness . 9/13 of the main sample ( and 9/16 of the total `` main + x - ray bright '' sample ) exhibit identifiable 9.7@xmath3 silicate absorption features ( s@xmath62 - 0.4 is defined in table [ tab : irs ] ] ; hereafter described as `` absorption - dominated '' sources and denoted by `` abs '' in table [ tab : irs ] ) . a further 4/13 or the main sample ( and 7/16 of the total `` main + x - ray bright '' sample ) exhibit power - law spectra with no convincing features ( hereafter described as `` power - law '' sources and denoted by `` pow '' in table [ tab : irs ] ) ; either they have only weak silicate absorption features or they are at @xmath63 and the absorption feature does not fall within the observable irs bandwidth . bootesx6 may have a weak silicate emission feature if it is at @xmath64=0.9 . given that this is highly uncertain without other convincing features in the spectrum , we classify bootesx6 as a power - law source . none of the sources show convincing pah emission features , although , given their uncertain or unknown redshifts , there may be weak pah emission in some individual sources . we discuss each class in turn . lllllllllllll bootesx1 & 240&480 & 1.7 & 12.2 & 12.6 & 13.3 & @xmath7 & @xmath70.4 & @xmath40.05 & @xmath41380 & @xmath412.8 & abs + bootesx2 & 360&720 & 0.9 & 11.5 & 11.8 & 12.5 & 3.3 & @xmath71.0 & @xmath40.04 & @xmath4190 & @xmath412.0 & abs + bootesx3 & 480&960 & 2.0@xmath44 & 12.2 & 12.6 & 13.3 & @xmath7 & @xmath70.4 & @xmath40.20 & @xmath41170 & @xmath412.9 & abs + bootesx4 & 360&720 & 1.12 & 12.2 & 12.4 & 13.1 & 2.4 & @xmath71.4 & @xmath40.04 & @xmath4450 & @xmath412.4 & abs + bootesx5 & 480&960 & 1.4 & 12.0 & 12.3 & 13.0 & 2.8 & @xmath70.4 & @xmath40.09 & @xmath4590 & @xmath412.5 & abs + bootesx6 & 360&720 & 0.9 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & pow / em ? + bootesx7 & 480&960 & 1.1 & 11.5 & 11.9 & 12.6 & 6.3 & @xmath70.5 & @xmath40.05 & @xmath4110 & @xmath411.7 & abs + bootesx8 & 480&960 & 2.1 & 12.3 & 12.5 & 13.2 & @xmath7 & @xmath70.6 & @xmath40.05 & @xmath4560 & @xmath412.5 & abs + bootesx9 & 480&960 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & pow + bootesx10 & 480&960 & 2.6 & 12.6 & 12.9 & 13.6 & @xmath7 & @xmath65 & @xmath40.10 & @xmath41670 & @xmath412.9 & abs + bootesx11 & 480&960 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & pow + bootesx12 & 480&960 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & pow + houck13 & 480&720 & 1.95 & 12.3 & 12.5 & 13.2 & @xmath7 & @xmath72.9 & @xmath40.03 & @xmath4420 & @xmath412.3 & abs + bootesx13 & 480&1200 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & pow + bootesx14 & 480&1200 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & pow + bootesx15 & 480&1200 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & @xmath7 & pow + + fig . 1 . continued . for the absorption - dominated sources , redshifts are determined primarily from the localized maximum in the irs continuum , or `` hump '' , which is blueward of the absorption feature . this feature is produced by absorption on either side of the feature , and with a possible contribution of 7.7@xmath61 m pah emission in composite sources . we determine redshifts by assuming this hump has a rest - frame wavelength of 7.9@xmath61 m ( see average spectra in @xcite and @xcite ) . comparison of irs redshifts with optical redshifts for similar absorbed sources ( e.g. , @xcite ; @xcite ) suggests that they can be uncertain to @xmath410.2 in @xmath64 . for the absorption - dominated sources , the overall nature of the infrared spectra can be best considered by assembling the average irs spectrum . this allows consistent features within individual spectra to be seen with improved signal - to - noise . this was achieved by wavelength correcting each individual unsmoothed spectrum to the rest - frame ( @xmath64=0 ) , interpolating them to a common wavelength scale of @xmath170.1@xmath3/pix , and taking a straight ( non - weighted ) average at each wavelength position . the averaged spectrum is shown in figure [ fig : xstack]a . the most dominant feature is the silicate absorption feature at 9.7@xmath3 . the average silicate absorption strength ( as defined in table [ tab : irs ] ) is @xmath66=@xmath71.0 ( with individual values ranging from @xmath70.4 to @xmath72.9 ) . for comparison , we also show the average spectrum of the absorption - dominated 70@xmath3-selected sources presented in @xcite ( figure [ fig : xstack]b ) . even though the x - ray - selected absorption - dominated sources have a similar average @xmath67[24 ] color to that of the 70@xmath3-selected absorption - dominated sources , they have a much shallower average silicate absorption ( @xmath66=@xmath71.0 compared to @xmath66=@xmath72.1 ) . the average silicate absorption of the x - ray sample is substantially less than the median value for local ulirgs ( @xcite ; @xcite ) and the optically obscured sample observed by @xcite and @xcite , and is slightly larger that the median value for seyfert 2 agn ( @xmath70.6 ; @xcite ) . the individual spectra show no evidence for pah emission ( 6.2@xmath3 equivalent width @xmath40.2@xmath3 ; see table [ tab : irs ] ) , although there is a hint of the 6.2 and 7.7@xmath3 pah features in the average spectrum . however , because of the redshift uncertainties for the individual spectra , it is difficult to be confident in any weak narrow emission line features that appear in the average . the possible feature at 7.7@xmath3 could also be due to the [ ne vi ] emission line at 7.6@xmath3 . for each individual source , we use the noise spectrum to estimate the maximum flux from the 6.2@xmath3 pah emission feature ( we estimate the flux of the nearest noise feature to 6.2@xmath3 ) . we then use the relation of @xcite to estimate the corresponding maximum sfr and infrared luminosity associated with star - formation . the values are shown in table [ tab : irs ] . in some cases , the spectra are not sensitive enough to put a useful limit on the sfr . bootesx2 and bootesx7 have the lowest limits of sfr@xmath4190 m@xmath68 yr@xmath38 and sfr@xmath4100 m@xmath68 yr@xmath38 respectively , corresponding to infrared luminosities associated with star - formation of log l@xmath6912.0 and @xmath411.7 respectively . comparing these values to the total infrared luminosity estimated from the rest - frame 8@xmath3 flux density , suggests that less than 30% and 13% of the total infrared luminosities are from star formation processes . weak indications are present in the average for [ ne ii ] , [ ne v ] , and [ ne iii ] emission lines . the relative intensities of these lines are @xmath170.7:1:1 . the presence of [ ne v ] is a strong agn indicator ( @xcite ; @xcite ) . the relative intensities show that [ ne v ] is stronger than that of local seyferts such as ngc 4151 , markarian 3 , and cena @xcite . if there is a contribution of 12.7@xmath3 pah emission to the [ ne ii ] line in the stacked spectrum , this would make this effect even larger . this may indicate a higher ionization of the narrow - line region by the more powerful agn in these sources . average irs spectrum of x - ray sources with redshifts ( top ) . for comparison , the average irs spectra of absorption - dominated sources 70@xmath3 sources from @xcite is also shown ( bottom ) . the expected positions of typically strong emission lines and the silicate absorption line are shown . the average spectrum combines the individual un - smoothed rest - frame spectra and is not smoothed.,title="fig:",height=226 ] average irs spectrum of x - ray sources with redshifts ( top ) . for comparison , the average irs spectra of absorption - dominated sources 70@xmath3 sources from @xcite is also shown ( bottom ) . the expected positions of typically strong emission lines and the silicate absorption line are shown . the average spectrum combines the individual un - smoothed rest - frame spectra and is not smoothed.,title="fig:",height=226 ] we have measured the luminosities at 5.8@xmath3 to determine the continuum luminosity just shortward of the 6.2@xmath61 m pah feature and at a wavelength without strong absorption ( e.g. , @xcite ; @xcite ; @xcite : see table [ tab : irs ] for individual values ) . the absorption dominated sources have median luminosity @xmath70l@xmath13(6@xmath61 m ) = @xmath71 ( 1.5 @xmath72 l@xmath73 ) . these are very luminous sources , exceeding that of most local agn in the sample of @xcite : sy 2 in that sample have median @xmath70l@xmath13(6@xmath61m)@xmath74l@xmath73 , and ulirgs have @xmath70l@xmath13(6@xmath61m)@xmath17 @xmath75l@xmath73 . @xcite find that local ulirgs span the range @xmath70l@xmath13(6@xmath61 m ) = 1@xmath76 l@xmath68 . our sources lie at the upper end of this range . the most luminous x - ray source , at @xmath70l@xmath13(6@xmath61m)=4 @xmath77 10@xmath78 l@xmath68 , is nearly as luminous as the most luminous source yet published from irs spectra : source 9 in @xcite with @xmath70l@xmath13(6@xmath61m)=5.9 @xmath77 10@xmath78 l@xmath68 . we estimate the total infrared luminosity , l@xmath6=l(8 - 1000@xmath3 ) of each of the absorption dominated sources . the conversion factors vary significantly depending on the template adopted for the conversion @xcite . because we expect the infrared emission to be dominated by obscured agn activity , we use the conversion for the template mrk 231 : l@xmath6=5@xmath79l@xmath13(8@xmath61 m ) , where the rest - frame 8@xmath3 flux density is measured directly from the irs spectra . the estimates are about a factor of 7 lower than one would obtain using templates of starburst - dominated galaxies such as arp 220 , and this explains our smaller l@xmath6 compared to that of @xcite for houck13 which was estimated from f00183 - 7111 . the infrared luminosities confirm that the absorption - dominated sources are all ultra - luminous ( @xmath8010@xmath81 ) or hyper - luminous ( @xmath8010@xmath82 ) infrared galaxies . given the lack of features and/or optical follow - up of the power - law sources , we do not have redshifts for these sources . we therefore can not construct an average spectrum or determine luminosities . the spectra of the power - law sources must have weak or absent silicate features ( 6.2@xmath3 pah equivalent widths @xmath830.2@xmath3 ) or they lie beyond @xmath842.6 , causing their absorption features to fall longward of the irs wavelength limit . it is difficult to determine whether silicate emission exists in these sources given our lack of redshift information and that the silicate emission feature is generally weaker than absorption feature . however bootesx6 may have a weak silicate emission feature if it is at @xmath64=0.9 . all 3 of the `` x - ray bright '' subsample are power - law sources .

nine of the x - ray sources show 9.7 silicate absorption features . we argue that the featureless spectra likely result from the sources having weak or absent silicate and pah features rather than the sources lying at higher redshifts where these features are shifted out of the irs spectral window .

we present mid - infrared spectroscopy of a sample of 16 optically faint infrared luminous galaxies obtained with the infrared spectrograph ( irs ) on the . these sources were jointly selected from and imaging surveys in the ndwfs botes field and were selected from their bright x - ray fluxes to host luminous agn . none of the spectra show significant emission from polycyclic aromatic hydrocarbons ( pahs ; 6.2 equivalent widths.2 ) , consistent with their infrared emission being dominated by agn . nine of the x - ray sources show 9.7 silicate absorption features . their redshifts are in the range , implying infrared luminosities of log(l)=12.5.6 . the average silicate absorption strength is not as strong as that of previously targeted optically faint infrared luminous galaxies with similar mid - infrared luminosities implying that the x - ray selection favors sources behind a smaller column of si - rich dust than non - x - ray selection . seven of the x - ray sources have featureless power - law mid - ir spectra . we argue that the featureless spectra likely result from the sources having weak or absent silicate and pah features rather than the sources lying at higher redshifts where these features are shifted out of the irs spectral window . we investigate whether there are any correlations between x - ray and infrared properties and find that sources with silicate absorption features tend to have fainter x - ray fluxes and harder x - ray spectra , indicating a weak relation between the amount of silicate absorption and column density of x - ray - absorbing gas .

0801.4578

c

all the x - ray selected sources have infrared spectra consistent with their mid - ir luminosities being dominated by emission originating from agn activity . this is expected given that their high x - ray luminosities imply that they host luminous agn which should dominate their infrared spectra . we find a larger fraction of power - law sources ( 4/13 of the main sample and 7/16 of the total ( main + `` x - ray bright '' ) sample ) than is found in the swire sample of @xcite ( they find only 1/9 to have a featureless power - law spectrum in their sample which has an x - ray limit which is @xmath85 fainter than that of our sample ) . this may in part be due to them having accurate optical redshifts , which make it easier to identify features . it could also be due to our selection of more luminous x - ray sources , which are less likely to be heavily obscured and exhibit silicate absorption . this hypothesis is supported by the fact that 6/7 of the power - law sources are also the brightest x - ray sources in the sample . to explain the lack of a silicate absorption feature in their irs spectra , the power - law sources must have weak or absent silicate features or they must lie beyond @xmath842.6 . we argue that the latter is unlikely given that they are among the brightest x - ray sources in our sample . if at @xmath862.6 , they must be extremely intrinsically luminous . assuming a canonical power - law spectrum with photon index , @xmath87=1.7 , the typical x - ray flux of f@xmath32=4 @xmath88 corresponds to a rest - frame x - ray luminosity of l@xmath32=2 @xmath89 at @xmath64=2.6 which would suggest that they were among the most powerful quasars known . if at @xmath63 , these sources would be significantly more x - ray luminous than any of the sources at @xmath90 . we would not expect a sharp difference in the luminosities of sources at higher redshifts . furthermore , only 0.7% of the @xmath171000 x - ray sources in the @xmath2 xbotes survey @xcite with spectroscopic redshifts from ages ( kochanek et al . in prep ) have luminosities this high . in the following discussion , we assume that these sources are at similar redshifts to the rest of the x - ray selected sources and that they must have weak or absent silicate features . in figure [ fig : irac ] , we show the irac color - color diagram for our irs sources . to increase the number of x - ray selected sources , we also plot the 9 x - ray selected irs sources from the lockman hole field of the swire survey presented by @xcite . the swire sample is selected to have f@xmath13(24@xmath3)@xmath240.9 mjy , f@xmath91 , and @xmath31 mag . the x - ray flux limit still corresponds to typical agn luminosities at these redshifts . to determine the location in color - color space of these sources in comparison to the general 24 @xmath3 population , we also plot the distribution of the @xmath2310,000 mips botes sources with f@xmath13(24@xmath3)@xmath240.5 mjy . the rough regions expected to be inhabited by different populations are shown . we also plot the empirical line of @xcite ( see also @xcite ) to separate agn - dominated sources from galactic stars and normal galaxies . 20/25 of the x - ray selected sources lie within the agn region of @xcite . @xcite show that large amounts of extinction ( a@xmath9250 ) toward the active nucleus and/or a large contribution from a starburst can cause the irac colors of an object to fall outside of the @xcite region . because our sources are largely within the agn region , they are unlikely to be heavily extincted or have a large starburst contribution to their mid - ir emission . there appears to be no correlation between the position in irac color - color space with the presence of the silicate absorption strength , again supporting the hypothesis that the silicate feature arises in the cooler gas which is traced by longer infrared wavelengths . the sources in the x - ray bright sub - sample appear to have slightly bluer colors which may demonstrate that they are less dust obscured . the irac color - color classification is expected to deteriorate at @xmath931 as the observed irac bands are pushed towards lower wavelengths in which the stellar light dominates over hot dust emission ( @xcite ; @xcite ) . however , it likely holds to higher redshifts for the most luminous sources because the near - infrared emission is still dominated by the hot dust , even in the integrated spectral energy distribution . in figure [ fig : opt_col ] , we show the 24-to-8 @xmath3 vs. 24-to-0.7 @xmath3 color - color diagram for our sources ( see @xcite for the location of different populations in this color - color space ) . the 24-to-8 @xmath3 and 24-to-0.7 @xmath3 colors are defined as f(24:8)=@xmath94[@xmath95/@xmath96 and f(24:r)=@xmath94[@xmath95/@xmath97 respectively . f(24:r ) is a good indicator of obscuration and/or redshift . f(24:8 ) has been used as a crude measure of the spectral slope and hence the dust temperature distribution and whether the source is agn- or starburst - dominated . @xcite find that agn - dominated sources tend to have f(24:8)@xmath40.3 and starburst - dominated sources tend to have f(24:8)@xmath240.3 . even though the x - ray selected sources must harbor a powerful agn , their 24-to-8 @xmath3 colors suggest that the sources are dominated by a combination of agn and starbursts . we suggest that this diagnostic breaks down for obscured sources due to the heavy absorption at near - ir wavelengths which will steepen the infrared slope regardless of the underlying power source . in addition , at @xmath981 - 2 , the silicate absorption feature is moving through the 24@xmath99 filter , complicating the interpretation further . the @xmath15-[24 ] colors of the x - ray selected sources are typically bluer than that of the most extreme irs sources presented in @xcite and @xcite which typically have @xmath100>$]15 ( f(24:r)@xmath241.83 ) . the faintest optical magnitude is relatively bright ( @xmath15=23.7 ) despite the fact that there is no optical selection criteria against including optically faint sources . we suggest that the x - ray - selection is biasing us against the most heavily absorbed ( and therefore optically faintest ) sources . indeed , the sources in the x - ray bright sub - sample have among the bluest @xmath15-[24 ] colors due at least partially to their relatively bright @xmath15-band magnitudes . figure [ fig : xabs ] shows the observed x - ray flux as a function of x - ray hardness ratio for the combined sample of botes and swire x - ray irs sources . there are no sources with both small x - ray fluxes and small x - ray hardness ratios . the grey - scale shows that this is not seen in the larger population of x - ray sources in the same redshift range , and only becomes apparent when we jointly select x - ray sources that are both infrared bright and optically faint . our selection criteria result in a sample of bolometrically luminous high redshift agn . in these cases , small observed x - ray fluxes will be associated with more obscured sources which will also have larger hardness ratios . for our combined sample , the absorption - dominated sources tend to have fainter x - ray fluxes and larger x - ray hardness ratios ( with a median value of hr=0.55 ) which are indicative of more absorbed x - ray spectra and larger hi column densities . conversely , the power - law sources have brighter x - ray fluxes and smaller hardness ratios ( with a median value of hr=@xmath70.2 ) indicative of less obscured x - ray spectra and smaller hi column densities . this suggests that the dusty absorbing regions responsible for the silicate absorption also contain sufficient gas to cause x - ray absorption or that both the gas and dust lie along similar lines of sight . deeper silicate absorption features may be associated with more embedded agn with higher column densities of gas . our results are consistent with those of @xcite who measure the silicate absorption depth for a sample of 85 nearby agn with x - ray data and find a correlation between the strength of the silicate feature and the hi column density . our lack of redshifts for the power - law sources means that we must compare the x - ray fluxes and hardness ratios rather than the x - ray luminosities and fitted hi column densities . any large difference in the redshift distribution of the two populations could affect our results ( for example higher redshift sources with identical x - ray luminosities will have softer x - ray spectra and smaller x - ray fluxes ) . however , in section [ sec : pow ] , we argue that the power - law sources lie at @xmath1012.6 and there is no reason to think that they lie at significantly different redshifts to the absorption - dominated sources given their similar selection criteria . although we find a trend in the x - ray and infrared properties of these sources , the correlations are only weak . the difficulty in establishing a clear relation between x - ray and infrared properties may be explained by the distribution of their gas and dust . @xcite show that the x - ray absorbing column density of seyfert 2 galaxies varies on yearly timescales for most sources . this suggests that most of the x - ray absorption must occur on sub - parsec scales . they obtain even tighter constraints in @xcite for a seyfert galaxy which exhibits spectral variation on timescales of days . this suggests that , at least for less powerful sources , the obscuring gas is on a similar scale to that of the broad - line region . significant amounts of dust are unlikely to lie at these distances because of the dust sublimation temperatures . the difference in the location of much of the gas and dust may explain the large scatter between parameters tracing the x - ray and mid - ir obscuration ( e.g. , @xcite ) . @xcite suggest that the obscuring material in dusty agn is likely to consist of both dense clumpy clouds of dust and a smoother inter - cloud medium . they argue that deep silicate absorption can only be produced in a source embedded in a smooth medium since clumpy clouds will provide direct views of portions of illuminated clouds which will fill in the resultant silicate absorption feature . since our x - ray selected sources have shallower silicate absorption features than typical ulirgs , this may suggest that they are dominated by clumpy obscuration . alternatively , they may simply have a smaller line of sight obscuration . @xcite obtained irs spectra for a sample of 7 x - ray selected agn which were specifically chosen to have large x - ray luminosities and large column densities of gas ( due to their large x - ray hardness ratios ) . given the correlation between hi column density and silicate absorption strength ( see discussion above and @xcite ) , we might expect them to exhibit deep silicate features . however , all of their sources exhibit featureless power - law spectra . the solution to this apparent problem may be that they selected a highly unusual population of sources which were both extremely x - ray luminous and x - ray obscured . figure [ fig : xabs ] shows that although x - ray obscured sources are more likely to have silicate absorption features , x - ray luminous sources are likely to have featureless power - law spectra . perhaps more luminous agn are more capable of breaking up the surrounding dust into discrete clouds which would fill in the silicate absorption feature in these cases despite the large column densities of gas . we compare the fraction of power - law dominated to absorption dominated sources in different samples . @xcite probe the lowest x - ray luminosities and find only 1/9 ( 11% ) are power - law dominated . our sample has higher x - ray luminosities and we find the fraction of power - law to absorption dominated sources to be 4/13 ( 31% ) in the main sample and 7/16 ( 43% ) in the total ( main + x - ray bright ) sample . all of the sources in the @xcite study are power - law dominated . their sources are particularly bright in the x - ray , with intrinsic x - ray luminosities in the range logl@xmath102=44.0 - 45.5 . this suggests that more x - ray luminous sources are more likely to have shallower silicate absorption ( which will appear as power - law sources ) . 0.5 - 7 kev band x - ray flux against x - ray hardness ratio for x - ray selected irs sources . the hardness ratios can range from 1 ( hardest x - ray spectrum ) to -1 ( softest x - ray spectrum ) . the botes x - ray selected sources are denoted by large blue symbols ( with the largest symbols denoting the x - ray bright sub - sample ) . the fainter x - ray sources from @xcite are also shown ( smaller red symbols ) . the sources are split into silicate absorption - dominated sources ( downwards triangles ) , and power - law dominated sources ( stars ) . poisson error bars are also shown . the grey scale shows the distribution of all x - ray sources in the xbotes survey with redshifts @xmath64=0.9 - 2.6.,height=188 ] @xcite , @xcite , and @xcite show that there is a strong relation between agn hard x - ray emission and mid - ir continuum in low redshift active galaxies . figure [ fig : xvs6 ] shows the agn continuum luminosity at 6@xmath3 as a function of 2 - 7 kev x - ray luminosity for the absorption - dominated sources ( the power - law sources could not be included because we do not have redshifts to derive the luminosities ) . although the absorption - dominated sources do not show a clear correlation between these two quantities , this lack is likely to be due to the large luminosity errors and relatively narrow luminosity range of the sample . when we compare our sources with lower luminosity sources at low redshift @xcite , we find that they form the higher luminosity extension of the relation . we have chosen not to correct the x - ray luminosity for absorption given the large uncertainties . 7/9 of our sources lie at l(2 - 7kev)/@xmath70l@xmath103(6@xmath3)@xmath40.1 , compared to only 8/47 of the @xcite sources ( before correcting for absorption ) . this suggests that our sources are generally more obscured than the low redshift , lower luminosity agn presented in @xcite . rest - frame 6@xmath3 luminosity against rest - frame absorption - uncorrected 2 - 7 kev x - ray luminosity for absorption - dominated botes sources ( blue triangles ) . the poisson error bars are shown for the x - ray luminosity . the low redshift iso sources from @xcite are plotted as small squares ( connected empty and filled squares denote x - ray luminosities uncorrected and corrected for x - ray absorption respectively ) . the solid line shows a direct correspondence between the x - ray and 6@xmath3 luminosities . the dotted lines show where l(2 - 7kev)=0.1 @xmath104(6@xmath105 and l(2 - 7kev)=0.01 @xmath104(6@xmath105.,height=188 ]

we investigate whether there are any correlations between x - ray and infrared properties and find that sources with silicate absorption features tend to have fainter x - ray fluxes and harder x - ray spectra , indicating a weak relation between the amount of silicate absorption and column density of x - ray - absorbing gas .

we present mid - infrared spectroscopy of a sample of 16 optically faint infrared luminous galaxies obtained with the infrared spectrograph ( irs ) on the . these sources were jointly selected from and imaging surveys in the ndwfs botes field and were selected from their bright x - ray fluxes to host luminous agn . none of the spectra show significant emission from polycyclic aromatic hydrocarbons ( pahs ; 6.2 equivalent widths.2 ) , consistent with their infrared emission being dominated by agn . nine of the x - ray sources show 9.7 silicate absorption features . their redshifts are in the range , implying infrared luminosities of log(l)=12.5.6 . the average silicate absorption strength is not as strong as that of previously targeted optically faint infrared luminous galaxies with similar mid - infrared luminosities implying that the x - ray selection favors sources behind a smaller column of si - rich dust than non - x - ray selection . seven of the x - ray sources have featureless power - law mid - ir spectra . we argue that the featureless spectra likely result from the sources having weak or absent silicate and pah features rather than the sources lying at higher redshifts where these features are shifted out of the irs spectral window . we investigate whether there are any correlations between x - ray and infrared properties and find that sources with silicate absorption features tend to have fainter x - ray fluxes and harder x - ray spectra , indicating a weak relation between the amount of silicate absorption and column density of x - ray - absorbing gas .

1410.8606

c

our primary finding is that the protoplanetary disk in hd 169142 possesses material that is within 1 au the star and undergoing changes to its structure on the order of a decade . a simple way to reduce the nir flux from observed pre-2000 levels to post-2000 levels is to reduce the scale height of the innermost edge of the disk . however , such a change would decrease the shadowing of the outer disk , and hence produce an anti - correlated variability of the inner and outer disk emissions , which is non - evident in the sed . hence , we have included in each of our models an optically thin population of small grains enveloping the optically thick sub - au mid - plane . changes to this optically thin structure do not produce major variations in the shadowing of the outer disk . the presence of such a structure is consistent with the results of @xcite who find that more realistic models of inner dust rims are insufficient to match bump "- like nir emission , as well as the results of @xcite who suggests that the standard puffed - up inner disk rims are insufficient to explain the nir excess of many herbig ae and related stars and that additional sources of nir emission must be present . we find three scenarios for the sub - au structures in the pre-2000 ( high nir flux ) state , one of which we may almost entirely exclude ( model c ) as it produces variable shadowing of the outer disk . we find nothing in the data to prefer either of the two remaining plausible scenarios over the other , although the changes between pre-2000 b @xmath65 post-2000 are much more dramatic than the changes between pre-2000 a @xmath65 post-2000 . in the scenario of our pre-2000 model a @xmath65 post-2000 model , the nir variability is explained through an inward shift of the outer edge of the sub - au structures toward the central star through accretion onto the star and perhaps other means . in the other scenario ( model b @xmath65 post-2000 state ) , the nir variability is explained through the continual vertical evacuation of material from the sub - au structures , leaving the post-2000 sub - au structures with a smaller vertical scale height than those structures in the pre-2000 state . while these two scenarios accurately reproduce observed pre-2000 nir flux levels through physically plausible mechanisms , we stress that the sed is highly degenerate to other structures and there exists a noteworthy potential for other presently unimagined possibilities . furthermore , we find that the dark ring observed between @xmath040 - 70 au in the polarized flux images is not the result of shadows cast by inner disk structures which are well constrained by the sed . instead , we find that this feature may be reproduced in the model images through scaling the density of the region by 0.3@xmath54 the value just outside of the gap , which is consistent with the density structure inferred through the 7 mm observations of @xcite . however , we find that the h - band images may also be reproduced by adjusting the scale height of the region by 0.86@xmath54 the value just outside of the gap . hence , further study of the multi - band imagery is necessary here to eliminate the degeneracy of these parameters and determine the true composition of the various dust grain sizes throughout the disk . extending to a distance comparable to between the orbits of uranus and neptune in our own solar system , the @xmath00.3 - 25 au gap in the protoplanetary disk in hd 169142 is temptingly explained through the clearing of material by planetary mass companions . however , there are other mechanisms which are likely to produce the inferred disk structure and which must be accounted for before we may speculate on which ( if any ) features may be the signature of young and forming planets . additionally , the timescale on which these mechanisms act to clear regions of the disk is of importance as the potential for planetary formation is significantly diminished with the decreasing supply of material . in a general overview of the evolution of protoplanetary disks , @xcite suggest that viscous accretion first dominates over photo - evaporation , until the mass accretion rate drops to @xmath66 . once these two counteracting processes become active on the same order of magnitude , the viscous flow of material from the outer disk will no longer be able to resupply the inner disk of material lost due to photo - evaporation , and an inner hole will be cleared . through analysis of the pa @xmath3 and br @xmath4 lines present in the may 2013 spex observations we derive a mass accretion rate of m @xmath5 @xmath67 . hence this accretion rate suggests that such a scenario may be an active clearing mechanism for the inner ( @xmath68 au ) gap . should this be the case , we may consider these to be ongoing processes within the presently observed state of the disk , as nir flux levels ( as of 2013 ) demand for the presence of material at sub - au radii . such a scenario is consistent with our speculative changes responsible for producing the variable nir emission ( see pre-2000 model a , in which the decrease in nir flux is explained through the shift of material inward toward the star , with a net mass loss of 6.3@xmath61m@xmath7 ) . we may also assume that the disk clearing mechanisms of grain - growth and coagulation into larger bodies , as well as large - scale sculpting by newly formed planets , may also be responsible for producing these observed structures . in fact , the results of our pre-2000 model a are suggestive that such additional clearing may plausibly be occurring , as our derived mass accretion rate accounts for as much as 2.7@xmath61m@xmath7 , or 43% of the total mass cleared over the observed timescale of the decrease in flux . this would leave room for other mechanisms to be actively clearing the region on the same order of magnitude as accretion onto the star . should a scenario such as this actually be underway , we could perhaps expect to see complete disappearance of the inner disk in hd 169142 on the order of another decade or so , prompting a change of class from pre - transitional to transitional disk . while the nir variability may be explained through the above scenario , there exists potential for other possibilities . another scenario in which the nir variability may be reproduced is one in which the optically thin envelope extends to higher altitude in the pre-2000 state than in the post-2000 state , as explored in our pre-2000 model b. this scenario matches pre-2000 nir flux levels with a shifting of the envelope by 0.07 au in the vertical direction and doubling its density as compared to the post-2000 model . while determining the exact mechanism and situations for which such a scenario may be relevant are beyond the scope of this paper , one likely possibility is that reconnection events ( like those present in the model of @xcite ) may be occurring within the magnetic field of a partially ionized inner disk , resulting in material which is lofted at altitude above the mid - plane . such proceedings would also help to explain the presence of the optically thin material which has been necessary throughout our constructions . similar considerations were explored for hd 163296 and hd 31648 in @xcite , and the migration of material at altitude above the inner disk was explored as a mechanism for producing the photometric variability observed in hd 163296 @xcite . however , given the chronology of the observed states , such a scenario would have material decreasing in altitude by 0.07 au and decreasing in density by a factor of 2 between the pre-2000 state and the post-2000 state . these changes , as well as those between our pre-2000 model c and post-2000 model are much more dramatic than those between the pre-2000 a and post-2000 models , and thus by invoking occam s razor we consider the chronology of our pre-2000 model a @xmath65 post-2000 model as being the most favorable of our presented scenarios . we obtain a null result for the dark ring between @xmath040 - 70 au being a shadow cast by inner structures , but rather we find that this feature may be reproduced in the model images by a net deficit in the density of scattering material in the region . hence we are left with the problem of how such structure in the disk might have originated and evolved from the primordial disk . again , large - scale sculpting by planetary mass companions is temptingly invoked as a mechanism for clearing this gap of material especially given its location beyond the snow - line and the large amount of gas available here for giant planet production . another possibility is that grain growth and coagulation may have been active within the region resulting in a net decrease in the density of micron sized grains and a corresponding increase in the density of grains with millimeter cross - sections . however , this seems unlikely as the 7 mm emissions suggest that the largest grains are concentrated within the @xmath025 - 40 au region , and not within the gap @xcite . this result is also consistent with a planet - induced dust filtration process ( as in @xcite ) being responsible for clearing of this gap , as in such a scenario the small grains should remain in the cavity while the millimeter sized grains are trapped at the edge . given the presence of large structures at smaller radii , photoevaporation falls even shorter of explaining the origin of this second gap . likewise , viscous flows of material to smaller radii seem unlikely , as this would raise new questions of why such a mechanism has preferentially cleared this region but not those at immediately larger or smaller radii . hence we are left to consider the intriguing and seemingly likely possibility that this second gap is a direct result of the formation of planets and their ongoing sculpting of this region of the disk . finally , there exists the possibility for the presence of multiple orbiting companions which may be responsible for the clearing of material , as well as sending material into orbit at altitude above the mid - plane ( which may explain the origin of the mini - envelope that we have found to be a necessary component ) . such companions may be on highly eccentric orbits , and at the inner parts of their orbits may travel close enough to perturb the sub - au disk structures on periods consistent with the @xmath010 yr timescale of the change in nir emission . furthermore , @xcite & @xcite have reported the independent l detection of planet - candidates respectively at separations of @xmath00.11 and 0.156"@xmath280.032 from the star . at a distance of 145 pc , these angular separations correspond to physical separations of @xmath016 au and 22.7@xmath284.7 au , placing them within the inner gap . both teams present observations lacking corresponding detections of the l hot - spots at shorter wavelengths , thus inferring their origin as sub - stellar . however , each team detects only one hot - spot , at differing radii , magnitude , and position - angle . hence the validation of these planet - candidates presently remains open to skepticism . incidentally , neither team detected l counterpart emission from the compact 7 mm source in @xcite . at 7 mm the disk is optically thin , raising the possibility of a chance coincidence with a background object . to be compelling , the l candidates need to be recovered again , and also seen in other filters ( such as 3.1 microns ) . nevertheless , the structures within the disk provide compelling evidence of planetary interactions and warrant the continued observation of the hd 169142 system as a candidate for the direct imaging of young extra - solar planets .

all observations known to us separate into two distinct states corresponding to a high near - ir state in the pre-2000 epoch and a low state in the post-2000 epoch , indicating activity within the au region of the disk . through analysis of the pa and br lines in our data we derive a mass accretion rate in may 2013 of m ( 1.5 - 2.7 ) x 10 m yr we find that shifting the outer edge ( au ) of the inner disk by 0.05 au toward the star ( in simulation of accretion and/or sculpting by forming planets ) successfully reproduces the shift in nir flux . we establish that the - 70 au dark ring imaged in the nir by and and at 7 mm by may be reproduced with a 30% scaled density profile throughout the region , strengthening the link to this structure being dynamically cleared by one or more planetary mass bodies .

we present near - ir and far - uv observations of the pre - transitional ( gapped ) disk in hd 169142 using nasa s infrared telescope facility and hubble space telescope . the combination of our data along with existing data sets into the broadband spectral energy distribution reveals variability of up to 45% between.5 - 10 m over a maximum timescale of 10 years . all observations known to us separate into two distinct states corresponding to a high near - ir state in the pre-2000 epoch and a low state in the post-2000 epoch , indicating activity within the au region of the disk . through analysis of the pa and br lines in our data we derive a mass accretion rate in may 2013 of m ( 1.5 - 2.7 ) x 10 m yr . we present a theoretical modeling analysis of the disk in hd 169142 using monte - carlo radiative transfer simulation software to explore the conditions and perhaps signs of planetary formation in our collection of 24 years of observations . we find that shifting the outer edge ( au ) of the inner disk by 0.05 au toward the star ( in simulation of accretion and/or sculpting by forming planets ) successfully reproduces the shift in nir flux . we establish that the - 70 au dark ring imaged in the nir by and and at 7 mm by may be reproduced with a 30% scaled density profile throughout the region , strengthening the link to this structure being dynamically cleared by one or more planetary mass bodies .

1410.8606

i

our assembly of the broadband sed from data sets covering a quarter of a century reveals variability of up to 45% at nir wavelengths over a maximum timescale of 10 years . through modeling of the sed we confirm several scenarios where changes to the inner ( sub - au ) structures may reproduce the two distinct states of the nir spectrum . the simplest of these involves a shift of the outer edge of the inner disk by @xmath00.05 au inward toward the star . in this scenario we have kept the density of the mid - plane the same by adjusting the total mass of the inner disk by 6.3@xmath61m@xmath7 to account for the decrease in volume . from the spex observations we derive a mass acrretion rate of m @xmath5 ( 1.5 - 2.7 ) x 10@xmath6 m@xmath7 yr@xmath8 , which accounts for as much as 43% of the total mass change in the above scenario , and is suggestive that other processes ( such as sculpting due to planets near the inner edge of the gap ) may be active in addition to accretion onto the star . however , we find that the pre-2000 sed may be equally reproduced if the density of the inner disk is allowed to increase , allowing for the change in mass to be equivalent to that lost due to accretion . in any event , we do not observe any variable shadowing of the outer disk , requiring that changes must be occurring within the outer edge of the inner disk , or to an optically thin structure above / below the mid - plane . in order to reproduce the level of variability we have found that the latter structure is a necessary component to provide heating of the outer portions of the inner disk , and is similar to components present in the models and predictions in other studies on related objects ( @xcite , @xcite , @xcite ) . through a combination of modeling the broadband sed and multi - band imagery we explore the structures of the outer disk and in particular the nature of the second gap detected in the h - band by @xcite and @xcite , and at 7 mm by @xcite . our models suggest that this ring in the nir is not significantly in part caused by shadows cast by inward disk structures . instead , we find that the dark ring in the nir may be reproduced by a 0.3@xmath54 scaling of density or a 0.86@xmath54 scaling of the height within the region . as a density feature is required to match the 7 mm observations , we find that a model fitting the images at both bands is possible with a density scaling @xmath55 and a height scaling of @xmath56 , which we leave for future studies to explore with the hopeful acquisition of additional mm - continuum imagery . in any event , this structure is highly suggestive of planetary formation within the region . we find that the most constrained outer disk structure in the sed is a wall at @xmath025 au , whose emission resembles a nearly single temperature black - body with t=120k . while maintaining fits to the sed , we find that the h - band polarized surface brightness profile @xmath69 between 85 - 120 au @xcite may be reproduced by a radial density profile @xmath57 and a scale height exponent @xmath70 , while a steeper profile @xmath51 may be reproduced with a steeper fall off to the density @xmath52 . similarly , we find that a density profile @xmath52 in the 35 - 70 au gap reproduces the observed surface brightness profile @xmath51 reported by @xcite for the region where r@xmath1150 au . finally , we conclude that the protoplanetary disk in hd 169142 is home to a multitude of structures which may indicate the activity of planetary formation processes , and perhaps even that the effects of such processes may be visible over a single person s lifetime . at the very least , it offers a unique perspective on the timescales and mechanisms by which such disks become cleared of material , and hence when and how planets have the opportunity to form . in any event , hd 169142 is a highly structured and evolving system , of which continued observation and investigation may reveal further details , as well as answer important questions about the formation and evolution of young planetary systems .

we present near - ir and far - uv observations of the pre - transitional ( gapped ) disk in hd 169142 using nasa s infrared telescope facility and hubble space telescope . the combination of our data along with existing data sets into the broadband spectral energy distribution reveals variability of up to 45% between.5 - 10 m over a maximum timescale of 10 years .

we present near - ir and far - uv observations of the pre - transitional ( gapped ) disk in hd 169142 using nasa s infrared telescope facility and hubble space telescope . the combination of our data along with existing data sets into the broadband spectral energy distribution reveals variability of up to 45% between.5 - 10 m over a maximum timescale of 10 years . all observations known to us separate into two distinct states corresponding to a high near - ir state in the pre-2000 epoch and a low state in the post-2000 epoch , indicating activity within the au region of the disk . through analysis of the pa and br lines in our data we derive a mass accretion rate in may 2013 of m ( 1.5 - 2.7 ) x 10 m yr . we present a theoretical modeling analysis of the disk in hd 169142 using monte - carlo radiative transfer simulation software to explore the conditions and perhaps signs of planetary formation in our collection of 24 years of observations . we find that shifting the outer edge ( au ) of the inner disk by 0.05 au toward the star ( in simulation of accretion and/or sculpting by forming planets ) successfully reproduces the shift in nir flux . we establish that the - 70 au dark ring imaged in the nir by and and at 7 mm by may be reproduced with a 30% scaled density profile throughout the region , strengthening the link to this structure being dynamically cleared by one or more planetary mass bodies .

0912.0907

i

a recent flurry of new mission proposals has renewed interest in measuring x - ray polarization from a variety of astrophysical sources . the gravity and extreme magnetism smex ( _ gems _ ) mission , which has recently been approved for funding in the latest round of nasa small explorer proposals , should be able to detect a degree of polarization @xmath3 for a flux of a few mcrab @xcite . a similar detector for the international x - ray observatory ( _ ixo _ ) could achieve sensitivity roughly @xmath4 greater ( @xmath5 degree of polarization ; jahoda et al . 2007 , costa et al . 2008 ) . projects like these could potentially detect a large number of galactic and extra - galactic sources at the @xmath6 level , including stellar - mass black holes , magnetars , pulsar wind nebulae , and active galactic nuclei . in this paper , we focus on accreting black holes ( bhs ) in the `` hard '' or `` steep power law '' state @xcite , which are characterized by a broad - band spectrum with a thermal peak around 1 kev and a strong high - energy power - law component extending above 100 kev . early estimates suggest that the typical level of polarization from these sources should be a few percent in the @xmath7 kev range , depending on the geometry of the accretion system and the inclination to the observer @xcite . we also extend these results to agn , whose hard x - ray properties are in many ways qualitatively similar . symmetry demands that in the newtonian limit the observed polarization from a flat disk must be either parallel or perpendicular to its rotation axis . however , the effects of relativistic beaming , gravitational lensing , and gravito - magnetic frame - dragging can break that symmetry and give a non - trivial net rotation to the integrated polarization vector . because the temperature in an accretion disk should increase closer to the bh , where these relativistic effects are strongest , it was predicted long ago that the observed angle and degree of polarization of thermal disk emission should depend on photon energy @xcite . in more recent years , discussion of polarization in accreting black holes has expanded to include a number of other aspects of thermal disk emission , such as uv and x - ray emission from agn disks @xcite and `` lamp post '' models for irradiating the accretion disk with a non - thermal source above the plane @xcite . quite recently , @xcite investigated the effect of atmospheric optical depth on the disk s polarization signal , and @xcite applied the original calculations of thermal x - ray polarization to the problem of measuring the inclination of the inner accretion disk . @xcite , using a monte carlo ray - tracing code on data from shearing - box simulations , estimated the effects of magnetic fields on the polarization of thermal emission . @xcite ( hereafter sk09 ) showed the importance of including returning radiation @xcite when calculating the polarization of bhs in the thermal state , an effect previously noted by @xcite . in addition to the relatively well - understood thermal state , it has also long been known that most agn and stellar - mass bhs can produce significant levels of harder x - rays with energies well above the thermal peak . in both cases , the hard flux is thought to be produced via inverse compton scattering of the disk photons in a corona of hot ( yet thermal ) electrons ( e.g. @xcite ) . from the shape of this hard spectrum , the basic geometry and optical depth of the corona may be constrained @xcite . despite these constraints , there remain sizable uncertainties about the nature and geometry of the hard x - ray emitting region . popular models for the hard state of stellar - mass bhs include a cool disk truncated at large radius ( @xmath8 ) surrounding a hot , radiatively inefficient flow @xcite , or alternatively a more extended disk surrounded by an optically thick hot corona , possibly in the form of a hot wind @xcite . even less is known about the steep power - law ( spl ) state . as for the hard state , most popular models are based on the inverse compton scattering of thermal seed photons from a thin disk surrounded by a hot corona @xcite , but bulk comptonization of a converging accretion flow has also been suggested @xcite . although the geometry of the corona could be as simple as a uniform slab in the spl state @xcite , the hard state of galactic bh binaries , as well as the x - ray emission from agn , are more likely caused by clumpy , inhomogeneous coronae , possibly caused by magnetic flares @xcite . here we explore the x - ray polarization signatures of three simple models for the corona geometry : a smooth sandwich with uniform optical depth in the vertical direction ; an inhomogeneous model made of a finite number of spherical clouds , randomly distributed above the disk ; and a truncated thin disk surrounding a spherical corona . in all cases , seed photons are emitted from the thermal , optically thick disk and are up - scattered in the hot corona ( in the truncated disk case , we also include low - energy seed photons embedded in the corona ) . we find that in all cases , the spectrum comprises a thermal peak ( @xmath9 kev for stellar - mass bhs ; @xmath10 ev for agn ) and a power - law component dominating above that , which typically makes up @xmath11 of the total flux . the gross features of the polarization spectra are quite robust : horizontal polarization with a few percent amplitude at low energies , with a transition to vertical orientation above the thermal peak , where the polarization amplitude can be as large as @xmath12 . the specific details of the polarization spectrum , i.e. , the amplitude of polarization at low and high energies , and the shape and location of the transition , provide constraints on the global geometry , temperature , and optical depth of the corona , as well as the bh mass , spin , accretion rate , and the observer inclination angle . in this paper , we begin in section [ methods ] with a brief overview of the computational methods used in the calculations . in sections [ wedge][sphere ] we present our results for three different corona geometries : sandwich , hot spots / clumps , and a sphere embedded in a truncated disk , all in the context of galactic x - ray binaries . in section [ agn ] , we apply the results to agn . in section [ discussion ] we discuss possible applications to observations .

these seed photons are then inverse - compton scattered through a hot ( but thermal ) corona , producing a hard x - ray power - law spectrum . we consider three different models for the corona geometry : a wedge `` sandwich '' with aspect ratio and vertically - integrated optical depth constant throughout the disk ; an inhomogeneous `` clumpy '' corona with a finite number of hot clouds distributed randomly above the disk within a wedge geometry ; and a spherical corona of uniform density , centered on the bh and surrounded by a truncated thermal disk with inner radius . in all cases

we present new calculations of x - ray polarization from accreting black holes ( bhs ) , using a monte - carlo ray - tracing code in full general relativity . in our model , an optically thick disk in the bh equatorial plane produces thermal seed photons with polarization oriented parallel to the disk surface . these seed photons are then inverse - compton scattered through a hot ( but thermal ) corona , producing a hard x - ray power - law spectrum . we consider three different models for the corona geometry : a wedge `` sandwich '' with aspect ratio and vertically - integrated optical depth constant throughout the disk ; an inhomogeneous `` clumpy '' corona with a finite number of hot clouds distributed randomly above the disk within a wedge geometry ; and a spherical corona of uniform density , centered on the bh and surrounded by a truncated thermal disk with inner radius . in all cases we find a characteristic transition from horizontal polarization at low energies to vertical polarization above the thermal peak ; the vertical direction is defined as the projection of the bh spin axis on the plane of the sky . we show how the details of the spectropolarization signal can be used to distinguish between these models and infer various properties of the corona and bh . although the bulk of this paper focuses on stellar - mass bhs , we also consider the effects of coronal scattering on the x - ray polarization signal from supermassive bhs in active galactic nuclei .

1309.2944

r

the reduced lightcurves are displayed in figure [ fig1 ] as a function of time for each of the five nights . immediately evident is the large decrease in brightness during the apparition that will be shown later to be simply due to the combination of increasing distance and increasing phase angle . gaps in the data on jan 12 and the apparent late start on jan 13 are due to clouds and/or the comet passing too close to a star . series of images having the best effective seeing from jan 13 and again from apr 6 were stacked to search for evidence of a coma ; none was detectable on either night . comparison of the wings of the comet s radial profile to stellar radial profiles on apr 4 and apr 6 ( when the non - sidereal motion was negligible ) suggests than any non - stellar component had an upper limit of 5% of the total cometary flux . therefore no coma removal was required ( or possible ) from these observations , unlike observations near perihelion . to remove the observed secular trend , we next performed a standard asteroidal normalization for these nuclear magnitudes to absolute values by correcting for heliocentric and geocentric distances and to zero phase angle , i.e. from the reduced magnitude , @xmath7 , to @xmath7(1,1,0 ) . our first attempts at normalization used the same linear phase function that we applied in our previous papers @xcite . this failed , however , to yield consistent brightnesses among the three observing runs no matter what phase coefficient was used . in retrospect , this was not surprising due to the much smaller phase angles involved in 2013 and the typical asteroidal non - linear opposition effect . rather than empirically determining the needed curvature , we decided to use a model phase curve that best matched c - type asteroids , those with physical characteristics such as albedo most similar to comet nuclei . fitting and interpolating the values from table iv of @xcite , we computed phase adjustments ( @xmath5@xmath8 ) for each night as given in table [ table1 ] . the resulting @xmath7(1,1,0 ) values at lightcurve maxima were in remarkable agreement , indicating that the phase function for tempel 2 s nucleus is indeed well - represented by c - type asteroids , and no further adjustments were applied . we continue to use our interactive period search routine for period determinations . as described in more detail in @xcite , phase plots are instantaneously updated as we systematically step through possible periods and examine by eye the tightness of resulting lightcurves . data are color - coded by date , making it easy to see small offsets in either brightness or phase throughout the phased curve . this is particularly useful when the intrinsic scatter due to photometric uncertainties is larger than usual , as we have here ; a slightly incorrect period will only have a very slight increase in scatter and most period search algorithms will not `` see '' that one day is offset from another . in fact , we also used the phase dispersion minimization method @xcite and , while this gave the same result , its uncertainty is much greater than what can be easily estimated from the color - coded phase plots , i.e. when clear shifts between observing runs is evident . note that standard routines can also misinterpret changes in the shape of the lightcurve , another factor here . our overall best observed period solution was 8.948@xmath00.001 hr , and the corresponding phase plot is shown in the top panel of figure [ fig2 ] . since there is no obvious preferred zero point for phasing , we choose 2013 jan 0.0 as this placed zero phase away from interesting features and the @xmath5@xmath9 values correspond to the day of the year ; prior to phasing , the @xmath5@xmath9 values were first corrected for light travel time from the observed mid - times in table [ table1 ] . as with previous apparitions , we have a double - peaked light curve where the two maxima are nearly identical in brightness but the minima are quite different , with the deeper minimum nearly `` v''-shaped while the smaller minimum varied in depth and shape with changing viewing geometry . unfortunately , our phase coverage is incomplete in april and the shallower minimum is not sampled , so we can not determine if the change in depth from january to march continued . also evident is a @xmath20.02 mag shift of much ( but not all ) of the jan 12 lightcurve from that of a day later on january 13 , for which we have been unable to identify a cause . while this has no effect on the the period solution , it alters the perception of the shape for the first half of the lightcurve . we also phased subsets of the data to look for evidence of a change in the observed period associated with the changing viewing geometries . as expected , phasing jan / apr yielded the same result as the entire data set , while a minor change was evident for the other two pairings jan / mar gave a slightly smaller value ( 8.947@xmath00.001 hr ) and mar / apr gave a slightly larger value ( 8.949@xmath00.002 hr ) with the higher uncertainty in the latter value directly caused by the shorter interval . within the uncertainties , this increase matches the predicted change of @xmath100.001 hr , caused simply by the earth s orbital motion between our earliest midpoint pairing and the latest ; the solar component to the synodic period near aphelion is both small and unchanging . these calculations all use the pole orientation from @xcite of r.a . = 162@xmath11 and dec . = @xmath1058@xmath11 ( and the diametrically opposite solution for retrograde rotation ) , but similar pole positions , such as from @xcite , would yield the same results . as discussed in the introduction , one goal of these observations was to uniquely discriminate between prograde and retrograde rotation for tempel 2 s nucleus . the sense of rotation always determines the sign of the solar component of the synodic period while the earth s component is unaffected by the direction of rotation . at the midpoint of our ensemble of measurements for 2013 , the solar and earth components are coincidentally nearly identical and in the prograde case have opposite signs that cancel out , resulting in the sidereal period being the same as the synodic ( 8.948@xmath00.001 hr ) , while in the retrograde case they compound yielding a sidereal value of 8.950@xmath00.001 hr . to determine which solution is correct , we next re - examine the solutions from 2010 . our overall observed ( synodic ) value was 8.950@xmath00.002 hr with a corresponding midpoint time of 2010 oct 25 or 112 days following perihelion @xcite . based on our water production rates throughout the apparition , over 95% of the total outgassing had taken place by this date . with an observed change in period of about @xmath100.004 hr per perihelion passage , we concluded that further torquing late in the 2010 apparition should be negligible and that the sidereal period in 2013 would therefore be unchanged from the late 2010 result . the corresponding sidereal values at the 2010 midpoint are 8.948 hr ( prograde ) and 8.955 hr ( retrograde ) . note that these values are slightly different from those listed in @xcite which erroneously only included the solar component but not the earth s component . with the expectation that the sidereal value should be the same in early 2013 as in late 2010 , and the possible sidereal values in 2013 being 8.948@xmath00.001 hr ( prograde ) and 8.950@xmath00.001 hr ( retrograde ) , we conclude that tempel 2 _ must _ be in prograde rotation , with a sidereal period in late 2010 and in early 2013 of 8.948 hr . as further evidence that tempel 2 is in a prograde rotation , we also examined the retrograde scenario . if it was the retrograde case , then as already stated the sidereal period in 2010 would have been 8.955 hr . since the difference between the retrograde synodic and sidereal periods in 2013 would be @xmath120.002 hr , we should have measured a period of 8.953 hr . phasing with this value is shown in the bottom panel of figure [ fig2 ] and it is clear that this solution does not yield a viable lightcurve , therefore the comet must instead be in prograde rotation . looking back at the earlier apparitions requires disentangling the synodic effects from the actual changes in period due to torquing . an early attempt to derive the sidereal period from the changing synodic period during 1988 @xcite suffered from several problems , including the claim of a smoothly decreasing period which could not be reproduced during a detailed reanalysis @xcite and our new determination that his synodic / sidereal modeling only included the earth s motion but neglected the dominant solar component . having now definitively determined the sense of rotation as prograde , we can reexamine prior apparitions . the computed sidereal periods for each epoch are given in table [ table3 ] ; for completeness and to illustrate the asymmetries of the pro- and retrograde solutions with respect to the observed synodic periods , we also tabulate the retrograde values . again , these values differ somewhat from the values given in @xcite since the earth component is now included along with the solar component , thereby causing the asymmetry . our conclusions regarding a decrease in the amount of spin - down remain unchanged from @xcite , with sidereal periods before perihelia in 1988 of 8.931 hr and in 1999 of 8.939 hr , for an average spin - down by 0.004 hr per apparition . the same rate of spin - down would have predicted a sidereal period of 8.951 hr in late 2010 , a larger change than we observe . we continue to think the most likely cause of this is the decrease in total water production from 1988 to 1999 and to 2010 , with lower production rates providing a smaller amount of torquing . however , within the uncertainties of the period determinations , the data are also consistent with no change in the rate of spin - down . the agreement between the late 1994 period with early 1999 also remains , with both yielding a sidereal period of 8.939 hr during an interval for which there was not an intervening perihelion passage . our 2013 lightcurves of tempel 2 revealed two unexpected findings . first , the amplitude within the lightcurve was smaller than we had assumed it would be and , second , the peak brightness was higher than predicted from earlier apparitions even after compensating for a non - linear phase function . after considering a variety of possibilities , such as removing too much or too little coma for differing apparitions or systematic effects when different filters were used , we think we have arrived at a self - consistent explanation . our expectations for 2013 were based on assuming that tempel 2 is a prolate ellipsoid with similar dimensions for the small and intermediate axes while the long axis is about 2.1@xmath3 greater . this is based on the 1988 thermal ir lightcurve from @xcite and that the sub - earth latitude then varied between @xmath121@xmath13 and @xmath129@xmath13 , i.e. the comet was viewed in 1988 nearly equator - on using our preferred pole solution . in early 2013 , the sub - earth latitude was @xmath1247@xmath13 , yielding a predicted amplitude of 0.4 mag , significantly greater than the observed value of @xmath20.2 mag . if , however , the intermediate axis is actually intermediate in length rather than the same as the small axis , then the total cross - section will appear to increase as one views from more pole - on and the amplitude will become even smaller than the simple function of the cosine of the sub - earth latitude ( the intermediate axis begins to dominate over the small axis ) . note that in this tri - axial case , it is the ratio of the long axis to the intermediate axis that determines the amplitude for the equator - on view . therefore , to explain the 1988 amplitude , the intermediate axis remains the same as originally assumed for the prolate case , and it is the short axis which must be even shorter . for our observed amplitude in 2013 , this requires the short axis to be less than one - third that of long axis , while the intermediate axis remains at about one - half of the long axis . this implies an even more elongated nucleus than the tri - axial solution with ratios of @xmath14 proposed by @xcite . in addition to explaining the observed amplitude , our tri - axial solution also naturally explains the increased brightness at lightcurve maxima in 2013 as being due to the increased total cross - section relative to the equator - on view . we strongly suspect , however , that the shape of the nucleus significantly departs from a tri - axial ellipsoid for several reasons . the lightcurve shape is not sinusoidal , but rather has one v-shaped minimum and one rounded minimum . also , the shapes and depths of the minima change rapidly in 2013 with only a small change in viewing geometries even though the sub - earth and sub - solar latitudes did not vary . finally , as discussed below , the amplitudes are quite different when the comet was viewed from high positive latitudes as compared to high negative latitudes . thus , we conclude that the nucleus must have large - scale protuberances . to first - order , the tri - axial ellipsoid explains most of the brightness and amplitudes measured at the other apparitions . most similar to 2013 were the circumstance in early 1987 with a sub - earth latitude of @xmath1252@xmath13 , and where jewitt & meech ( 1988 ) measured an amplitude of @xmath20.3 mag and a peak magnitude essentially identical to our 2013 value once adjustments are made for filter and phase angle . the 1999 apparition was nearly identical to that of 1988 , and the lightcurve characteristics are also essentially the same . the peak brightness in 1994 @xcite is also consistent with 1988 and 1999 but the amplitude is somewhat smaller ( by @xmath20.10.2 mag ) with no clear explanation since the sub - earth latitude was close to the equator . most different were our results from 2010 @xcite , where the peak brightness is @xmath20.20.3 mag fainter while the amplitude is larger than expected for a sub - earth latitude near @xmath1040@xmath13 . while an over removal of coma might partially explain both aspects , our methodology was the same used for the 1999 apparition which has no such issues , leading us to suspect that tempel 2 s actual shape characteristics are another significant factor ; this is supported by the fact that only in 2010 did the sub - earth latitude have a high positive value ( @xmath1040@xmath13 ) while all other apparitions were either near the equator ( 1988 , 1994 , 1999 ) or at high negative values ( 1987 , 2013 ) .

first , to determine its current rotation period and compare it to that measured shortly after its most recent perihelion passage in 2010 , and second , to disentangle the spin - down from synodic effects due to the solar day and the earth s orbital motion and to determine the sense of rotation , i.e. prograde or retrograde . at our midpoint of 2013 feb 24 , the observed synodic period is 8.948.001 hr , exactly matching the predicted prograde rotation solution based on 2010 results , and yields a sidereal period of the identical value due to the solar and earth synodic components just canceling out during the interval of the 2013 observations . the retrograde solution is ruled out because the associated sidereal periods in 2010 and 2013 are quite different even though we know that extremely little outgassing , needed to produce torques , occurred in this interval . with a definitive sense of rotation , the specific amounts of spin - down to the sidereal period could be assessed .

we present new lightcurve measurements of comet 10p / tempel 2 carried out with lowell observatory s discovery channel telescope in early 2013 when the comet was at aphelion . these data represent some of the first science obtained with this new 4.3-m facility . with tempel 2 having been observed to exhibit a small but ongoing spin - down in its rotation period for over two decades , our primary goals at this time were two - fold . first , to determine its current rotation period and compare it to that measured shortly after its most recent perihelion passage in 2010 , and second , to disentangle the spin - down from synodic effects due to the solar day and the earth s orbital motion and to determine the sense of rotation , i.e. prograde or retrograde . at our midpoint of 2013 feb 24 , the observed synodic period is 8.948.001 hr , exactly matching the predicted prograde rotation solution based on 2010 results , and yields a sidereal period of the identical value due to the solar and earth synodic components just canceling out during the interval of the 2013 observations . the retrograde solution is ruled out because the associated sidereal periods in 2010 and 2013 are quite different even though we know that extremely little outgassing , needed to produce torques , occurred in this interval . with a definitive sense of rotation , the specific amounts of spin - down to the sidereal period could be assessed . the nominal values imply that the rate of spin - down has decreased over time , consistent with the secular drop in water production since 1988 . our data also exhibited an unexpectedly small lightcurve amplitude which appears to be associated with viewing from a large , negative sub - earth latitude , and a lightcurve shape deviating from a simple sinusoid implying a highly irregularly shaped nucleus .

1309.2944

c

the observations reported here represent some of the first science collected with lowell observatory s new discovery channel telescope . despite a few problems associated with a facility still in the early stages of commissioning , we were able to easily fulfill our major science objectives regarding comet tempel 2 s rotational state , in spite of a smaller lightcurve amplitude than expected . we obtained a precise measurement of its current rotation period that , when combined with our 2010 measurements , yielded a definitive determination of its sense of rotation . this result in turn allowed us to determine the correct sidereal period associated with observed synodic values at each prior apparition . for lowell observatory and its partners , a new era has begun in which projects requiring time - intensive or long - duration observations can be accomplished for targets much fainter than have ever been possible . in the specific case of comet nuclei , we can now measure lightcurves of comet nuclei far from perihelion . the measured periodicity in a nucleus lightcurve depends on the changing cross - section both as illuminated by the sun and as seen from the earth , and in turn depends on the solar day as well as the earth s motion with respect to the comet and the sun . disentangling these effects from the change in the physical rotation due to torquing had been problematic at best . however , the relative importance of the solar component and earth s motion component are quite different far from the sun as compared to near perihelion . because of this , we planned and executed these new observations . the resulting synodic period , 8.948@xmath00.001 hr , matched that expected for the prograde scenario from 2010 while the nominal period associated with the retrograde solution is clearly ruled out . we therefore conclude that tempel 2 s rotation is prograde with respect to both the ecliptic and to its orbital plane . the sidereal period , 8.948@xmath00.001 hr , is coincidentally identical to the synodic value as the solar and earth components of the synodic period just cancel out during the interval of our 2013 observations . the new data also confirm that no additional spin - down took place following our late 2010 measurements , consistent with the water production curve showing a near - cessation of activity by that time . this lack of a change in the sidereal period very late in the 2010 apparition thereby implies that the smaller change in the period per perihelion passage between 1999 and 2010 as compared to 1988 to 1999 is real ( although a constant rate of spin - down can not be excluded within the uncertainties ) . note that the inferred changes match those given by @xcite for the prograde case . thus our hypothesis that a decrease in torquing is associated with the secular decrease in water production from 1988 to 2010 is probably correct . we note , however , that there is no strong evidence for a long - term decrease in activity over the past century , and the secular drop over the past two decades may reverse as the surface is eroded and varying proportions of ice are exposed from successive perihelion passages . similar to prior apparitions , the light curve is double - peaked with near - equal maxima but quite differently shaped minima . the shape and depth of one of the minima also changed over the three - month interval , another trait observed in the past . both characteristics directly indicate that the shape of tempel 2 s nucleus is not a simple prolate ellipsoid or even a triaxial ellipsoid but must instead have large - scale protuberances to cause such clear changes in the lightcurve from such a small change in viewing geometries ( @xmath120@xmath13 ) and essentially no change in sub - earth and sub - solar latitudes . the unexpectedly small amplitude we measured in the lightcurve ( @xmath20.2 mag ) appears to also be due to peculiarities of the nucleus shape our value is in good agreement with the only other data obtained at a similar sub - earth latitude @xcite , while data taken from near - equator on or from the other hemisphere all exhibit a much larger amplitude . the data further suggest that the length of the short axis is substantially shorter than that of the intermediate axis , though the shape is probably not as extreme as that of comet 103p / hartley 2 as imaged from epoxi @xcite . thus a more complete story of the properties of tempel 2 s nucleus is beginning to emerge . while determining the detailed shape must continue to await an upclose view tempel 2 was the proposed target of the planned comet rendezvous asteroid flyby mission more than two decades ago additional numerical modeling and new investigations from afar can continue to reveal clues to its physical structure and evolving behavior .

we present new lightcurve measurements of comet 10p / tempel 2 carried out with lowell observatory s discovery channel telescope in early 2013 when the comet was at aphelion . these data represent some of the first science obtained with this new 4.3-m facility . with tempel 2 the nominal values imply that the rate of spin - down has decreased over time , consistent with the secular drop in water production since 1988 . our data also exhibited an unexpectedly small lightcurve amplitude which appears to be associated with viewing from a large , negative sub - earth latitude , and a lightcurve shape deviating from a simple sinusoid implying a highly irregularly shaped nucleus .

we present new lightcurve measurements of comet 10p / tempel 2 carried out with lowell observatory s discovery channel telescope in early 2013 when the comet was at aphelion . these data represent some of the first science obtained with this new 4.3-m facility . with tempel 2 having been observed to exhibit a small but ongoing spin - down in its rotation period for over two decades , our primary goals at this time were two - fold . first , to determine its current rotation period and compare it to that measured shortly after its most recent perihelion passage in 2010 , and second , to disentangle the spin - down from synodic effects due to the solar day and the earth s orbital motion and to determine the sense of rotation , i.e. prograde or retrograde . at our midpoint of 2013 feb 24 , the observed synodic period is 8.948.001 hr , exactly matching the predicted prograde rotation solution based on 2010 results , and yields a sidereal period of the identical value due to the solar and earth synodic components just canceling out during the interval of the 2013 observations . the retrograde solution is ruled out because the associated sidereal periods in 2010 and 2013 are quite different even though we know that extremely little outgassing , needed to produce torques , occurred in this interval . with a definitive sense of rotation , the specific amounts of spin - down to the sidereal period could be assessed . the nominal values imply that the rate of spin - down has decreased over time , consistent with the secular drop in water production since 1988 . our data also exhibited an unexpectedly small lightcurve amplitude which appears to be associated with viewing from a large , negative sub - earth latitude , and a lightcurve shape deviating from a simple sinusoid implying a highly irregularly shaped nucleus .

1505.06415

i

there has been growing interest recently , both experimentally @xcite and theoretically @xcite , in the processes @xmath0 and @xmath1 , the single inclusive production of a hadron or jet at large transverse momentum in lepton - nucleon scattering . in contrast to the far more customary process @xmath2 @xcite , for @xmath0 the scattered lepton in the final state is not observed , so that the process is truly one - hadron ( or one - jet ) inclusive . the reason for the interest in @xmath0 comes from the study of single transverse - spin phenomena in hadronic scattering processes . it is well known that large single - spin asymmetries have been observed @xcite for the process @xmath3 , where @xmath4 denotes a transversely polarized proton . to explain the large size of the asymmetries , and their persistence all the way from fixed - target to collider energies , has posed a major challenge to theory . although a lot has been learned , it is fair to say that a fully satisfactory understanding has yet to be obtained . measurements of corresponding asymmetries in the kinematically equivalent , but much simpler , processes @xmath5 , @xmath6 have the promise to shed new light on the mechanisms for single - spin asymmetries in qcd . first fairly precise experimental data for @xmath5 have recently been released by the hermes @xcite and jefferson lab hall a @xcite collaborations . we note that at first sight one might consider the related process @xmath7 ( which is just the standard inclusive deep - inelastic ( dis ) process ) to be equally suited for transverse - spin studies in lepton scattering . however , the analysis of the corresponding single - spin asymmetry is considerably more complex because higher order qed effects are required for the asymmetry to be non - vanishing @xcite . in the same spirit as @xmath5 , also the processes @xmath8 @xcite with longitudinal polarization of the lepton and @xmath9 @xcite with a transversely polarized @xmath10 hyperon have been considered in the literature recently . the proven method for analyzing single - inclusive processes such as @xmath11 or @xmath0 at large transverse momentum rests on qcd perturbation theory and collinear factorization . for single - transverse - spin observables , this involves a twist-3 formalism in terms of three - parton correlation functions of the nucleon or the fragmentation process @xcite . interestingly , the recent study @xcite suggests that the twist-3 fragmentation effects could be the dominant source of the observed large transverse - spin asymmetries in @xmath3 . an alternative approach for describing the single - spin asymmetry in inclusive hadron production in @xmath3 was devised in the context of a `` generalized '' parton model in which the dependence of parton distributions and fragmentation functions on transverse momentum is kept @xcite . although no such factorization in transverse momentum is known to be valid for a single - inclusive cross section , the approach has enjoyed considerable phenomenological success . both the collinear twist-3 approach and the generalized parton model have been used to obtain predictions for the spin asymmetry in @xmath5 . in ref . @xcite a leading order ( lo ) twist-3 analysis has been presented in terms of parton correlation functions that were previously extracted from data for @xmath3 . the results obtained in this way fail to describe the hermes data @xcite for the spin asymmetries in @xmath5 . a comparison of perturbative calculations to the corresponding jlab data @xcite is not possible as the data are for hadrons with transverse momenta below 1 gev . the lo generalized parton model approach , on the other hand , appears to give results quite consistent with the hermes data @xcite . in our view it is premature to draw any conclusions from these findings at lo . given the kinematics ( and the precision ) of the present data , one may expect higher - order qcd corrections to the cross sections and the asymmetry to be important @xcite for a meaningful comparison of data and theory . at least next - to - leading order ( nlo ) corrections should be included . we stress that the twist-3 formalism , although so far only developed to lo , offers a well - defined framework for a perturbative study of the transverse - spin asymmetry in @xmath5 . this is in contrast to the generalized parton model , for which there is likely no systematic way of going to higher orders in perturbation theory . that said , nlo calculations within the twist-3 formalism are technically very challenging , and only a few nlo calculations have been performed for the simpler drell - yan @xcite and semi - inclusive deep - inelastic scattering ( dis ) cases @xcite . in the present paper , we take a first step toward an nlo calculation of the transverse - spin asymmetry for @xmath5 by computing the nlo corrections to the spin - averaged cross section for the process , which constitutes the denominator of the spin asymmetry . we present analytical results for the nlo partonic cross sections . to our knowledge , despite the vast amount of work performed for lepton proton scattering in the literature ( see , for example @xcite ) , this calculation has not been presented so far . we also present similar nlo calculations for the process @xmath1 . we note that the process @xmath1 has also been extensively studied in terms of the concept of `` 1-jettiness '' @xcite . here one additionally writes the cross section differential in a variable @xmath12 that characterizes the hadronic final state that is _ not _ associated with the produced jet or the nucleon beam remnant . in ref . @xcite the full nlo corrections for the 1-jettiness were computed , where a fully numerical approach was adopted . in principle , it should be possible to recover our nlo results by performing a ( numerical ) integration over @xmath12 of the results of @xcite . because of the propagator of the exchanged photon , the cross section for @xmath5 will contain contributions for which the photon is almost on - shell . this is not yet the case at lo where the high transverse momentum of the produced hadron requires the photon to be highly virtual . starting from nlo , however , it may happen that the incoming lepton radiates the photon almost collinearly . this may then be followed by a @xmath13 scattering process of the photon with a parton in the nucleon , which is perfectly capable of producing the hadron at high @xmath14 . in processes where the scattered lepton is observed , such as @xmath2 , one can in fact select such contributions by requiring the scattered lepton to have a low scattering angle . the incoming lepton then effectively acts merely as a source of quasi - real photons , and the process may be very accurately described in terms of a ( perturbative ) distribution function for photons in leptons known as the weizscker - williams ( ww ) distribution @xcite . this approach has been widely used with much success in the hera physics program @xcite . in the context of our nlo calculation for @xmath0 it is therefore interesting to investigate whether also in this case the contributions by almost real photons dominate and the nlo corrections may be well approximated by a weizscker - williams type distribution . since it is much easier to compute the latter contribution than the full nlo correction , this would mean that one could also obtain approximate nlo results for the transversely polarized cross section within the twist-3 framework by simply considering real photons . given the complexity of a full nlo calculation for the twist-3 case , this would be a tremendous advantage . we note that the contributions to the spin - dependent cross sections for @xmath15 for real photons were discussed in @xcite , including the twist-3 contributions for the single - transverse spin case . actual lo calculations for the twist-2 longitudinal spin - dependent cross section were presented in ref . @xcite for quasi - real photons . we will closely examine the contributions by quasi - real photons also in our paper . their relevance will of course also depend on the lepton species that is used , because the lepton mass leads to a lower limit on the virtuality of the photon . our paper is structured as follows . in sec . [ nlocalc ] we present our nlo calculations for the partonic cross sections for @xmath5 and @xmath1 . we also discuss in some detail the weizscker - williams contribution and how the calculation can be done keeping a finite lepton mass . section [ pheno ] presents numerical predictions for the nlo cross section to be expected at various fixed - target experiments and at a future electron ion collider ( eic ) . finally , we summarize our results in sec . [ concl ] .

the main feature of these processes is that the scattered lepton is not observed , so that the hard scale that makes them perturbative is set by the transverse momentum of the hadron or jet . kinematically , the two processes thus become direct analogs of single - inclusive production in hadronic collisions which , as has been pointed out in the literature , makes them promising tools for exploring transverse spin phenomena in qcd when the incident nucleon is transversely polarized . we find that the nlo corrections are sizable for the spin - averaged cross section . we present numerical estimates of the cross sections for present - day fixed target experiments and for a possible future electron ion collider .

we present next - to - leading order ( nlo ) perturbative - qcd calculations of the cross sections for and . the main feature of these processes is that the scattered lepton is not observed , so that the hard scale that makes them perturbative is set by the transverse momentum of the hadron or jet . kinematically , the two processes thus become direct analogs of single - inclusive production in hadronic collisions which , as has been pointed out in the literature , makes them promising tools for exploring transverse spin phenomena in qcd when the incident nucleon is transversely polarized . we find that the nlo corrections are sizable for the spin - averaged cross section . we also investigate in how far the scattering is dominated by the exchange of almost real ( weizscker - williams ) photons . we present numerical estimates of the cross sections for present - day fixed target experiments and for a possible future electron ion collider .

0709.2915

c

the results from sextractor were used to map the ages of each region according to their azimuthal location in the ring . the right panels of figure 5 show the resolved regions , which are color - coded according to age , in terms of ew . we assigned the physical center of the ring ( as computed with ellipse ) to be ( 0,0 ) , and viewed an region s azimuthal position in a counter - clockwise rotation from north to east . the color ranges are unique to each ring and , thus , do not denote the same ews for all rings . although we did not deproject the rings , all regions have a unique position , which allows us to search for any unambiguous distribution patterns . the pa of the major axes of the ring and the bar are indicated in the image . to complement the images , plots are shown in the left panels , which graph the log(ew ) versus pa , and again indicate the pas of the ring and bar major axes . we use @xmath30 color index maps , shown in figure 8 , as morphological indicators of the ring kinematics . these maps provide direct tracers of the bar dust lanes , which show the flow of gas to the ring . in the cases where the dust lanes were present , the azimuthal direction of the ring rotation was consistent with that of the galaxy in all cases . the contact points of the dust lanes with the ring are clearly visible in most of our images and indicate an offset of @xmath690@xmath31 between the contact points and the bar ( see section 6.3 for details ) . the dust lanes also show directional flow around the ring , assuming that rotation continues in the same direction as seen with the bar dust lanes and spiral arms . the adopted rotational direction of the rings is listed in table 2 and indicated for each ring containing a bar in figure 5 . we find that several galaxies , both barred and non - barred , exhibit relative azimuthal age gradients within the ring , as also observed by ryder , knapen , & takamiya ( 2001 ) and allard et al . ( 2006 ) for ngc 4321 . we only consider age gradients over a significant portion of the ring ( greater than 25% of the ring ) with amplitudes that exceed the uncertainties for differentiating between points over the range of interest . we highlight our findings below , and summarize the characterization of the age distributions for all of the rings ( e.g. , azimuthal gradient , radial gradient , flat distribution , or no recognizable pattern ) in table 3 ( column 2 ) . * ngc 278 ( fig . 5a ) : the entire ring as seen in @xmath0 is very small in size ( 0.2 kpc in radius ) with 20 individual regions detected that comprise the ring . this ring is the smallest one recognized in the galaxy ; a second `` outer '' nuclear ring appears at @xmath6 1 kpc and is discussed in detail in knapen et al . this outer ring is considered non - standard as it is very wide , and more a region of star formation with rather abrupt delimitations on the inner and outer radial range . in addition to this , we were in practice unable to derive a recognizable ring pattern of regions using sextractor , and have thus opted for concentrating on the inner nuclear ring . the host galaxy does not contain a bar in the optical nor near - ir wavelengths ( knapen et al . there is a decrease in the log(ew ) ( i.e. , an increase in age ) over approximately one third of the inner ring ranging from the positions of the regions centered at azimuth 124@xmath32 to 236@xmath32 . this indicates a counterclockwise rotation within the ring . a radial gradient spans the same range , with the younger regions lying on the inner side of the ring . a similar pattern , although not as clearly defined , appears over the range of 12@xmath32 to 100@xmath32 . * ngc 473 ( fig . 5b ) : two - thirds of the ring can be seen in the @xmath0 image , defined by 27 regions . a galactic bar exists at a major axis pa of 164@xmath32 along the major axis . the bar dust lanes indicate a counterclockwise flow of material around the ring . there is a sharply sloped age gradient over the range of 38@xmath32 to 203@xmath32 from younger to older , respectively . * ngc 613 ( fig . 5c ) : there exists a small partial nuclear ring containing 11 individual star - forming regions with a strong nucleus . a fairly flat distribution in the log(ew ) appears around the entire ring with ages averaging no less than 10 myrs . the galactic bar is located at pa = 110@xmath32 along its major axis . although a gradient is not defined , one of the contact points ( at 200@xmath32 ) coincides within 5@xmath32 to the youngest hotspot ( pa = 205@xmath32 ) in its respective hemisphere . * ngc 1300 ( fig . 5d ) : twelve regions form a small complete ring in @xmath0 although there is no clear pattern in ews . * ngc 1343 ( fig . 5e ) : the ring in this barred spiral galaxy is seen as complete in @xmath0 with 20 resolved regions . the mapping of ew to region location indicates a clear bi - polar age pattern around the ring with ew maxima ( i.e. , relative youngest age in the ring ) at pa = 140 and 309@xmath32 . there is a distinct age gradient approximately from one contact point to the other contact point ( located at 172@xmath32 and 352@xmath32 , respectively ) , where the age increases counterclockwise from the bar contact points . * ngc 1530 ( fig . 5f ) : three - quarters of the ring can be seen in @xmath0 containing 9 distinct regions . the galaxy has a large bar at pa = 122@xmath32 and two open spiral arms originating from its ends , rotating clockwise . we find bipolar age gradients , one in each hemisphere , as bisected by the position of the bar . the youngest regions are near the bar pa , ( i.e. , not the contact points ) over the range of 283 to 207 and 115 to 7 , with the ring rotation also clockwise . half of the ring is distinctly younger than the other half , where the turnover points coincide with the ring major axis pa (= 25@xmath32 ) . * ngc 4303 ( fig . 5 g ) : only seven regions define the small ring . the ring is observed to be three - quarters complete in @xmath0 with bipolar age maxima at pa = 114@xmath32 and 304@xmath32 . there are no obvious age gradients in between the maxima , but the latter are offset by less than 25@xmath32 from the bar contact points ( 100@xmath32 and 280@xmath32 ) . * ngc 4314 ( fig . 5h ) : the small ring consists of 10 regions showing a smooth and well - defined age gradient . the age gradient flows from older to younger in the same direction as the presumed ring rotation ( clockwise ) . the youngest region is within 20@xmath32 of one of the contact points ( pa = 45@xmath32 ) . * ngc 4321 ( fig . 5i ) : the well resolved full ring contains 57 detected regions . because missing data prevent the calculation of @xmath0 equivalent widths and ages , we refer to allard et al . ( 2006 ) for a similar analysis in @xmath33 . they find a bipolar age gradient corresponding to the ring pa ( at 170 and 350 ) and the location of the youngest region in each hemisphere . the age increases in a counter - clockwise direction along the direction of flow in the ring . * ngc 5248 ( fig . 5j ) : nineteen regions define the full , elliptically shaped ring . the youngest region is located 4@xmath32 away from of one of the bar contact points ( pa = 47@xmath32 ) . * ngc 5728 ( fig . 5k ) : eighteen regions define the partial ring , which is three - quarters complete . a very steep but small gradient exists from pa = 147@xmath32 to pa = 98@xmath32 from younger to older , according to the clockwise directional flow of the ring . one contact point ( pa = 303@xmath32 ) is within 2@xmath32 of the youngest region in the ring . the second youngest region ( pa = 147@xmath32 ) is within 24@xmath32 of the second contact point ( pa = 123@xmath32 ) , although it does precede that contact point . * ngc 5905 ( fig . 5l ) : the ring is small but complete in @xmath0 . it consists of nine regions and is relatively flat with respect to age ( except for one region ) . there appears to be no correlation in age with respect to the bar contact points . * ngc 5945 ( fig . 5 m ) : only three regions define this patchy ring , which contains low ew values ( all less than 1.5 in the log ) . buta & crocker ( 1993 ) indicate a nuclear ring , but our images do not have enough resolution to confirm this . * ngc 5953 ( fig . 5n ) : the non - barred galaxy has a nuclear ring that appears complete with 23 regions . although we know of no bar to directly fuel the ring , it is well formed and resolved both azimuthally and radially . * ngc 6503 ( fig . 5o ) : the elliptically shaped ring contains 84 resolved regions in this unbarred spiral . no gradients are evident . * ngc 6951 ( fig . 5p ) : the ring is small but complete with eight detected regions . the youngest region ( pa = 339@xmath32 ) is within 16@xmath32 of its respective contact point . the ages steeply increase ( by a factor of 10 ) from 339@xmath32 to 218@xmath32 in a clockwise direction , consistent with the directional flow of the galaxy . * ngc 7217 ( fig . 5q ) : the ring is three - quarters complete in @xmath0 . twenty - two regions were detected in the ring of this unbarred galaxy . ages increase in a clockwise direction from pa = 109@xmath32 to pa = 6@xmath32 . * ic 1438 ( fig . 5r ) : this barred galaxy hosts a complete ring with 11 regions detected . there exists an increasing age gradient from pa = 32@xmath32 to pa = 211@xmath32 in a counterclockwise direction . this direction is consistent with the ring rotational flow . the youngest region is within 2@xmath32 of its respective bar contact point ( pa = 304@xmath32 ) * ngc 7570 ( fig . 5s ) : eighteen regions comprise a mostly complete ring in this barred galaxy . an increasing age gradient ranges counterclockwise from pa = 112@xmath32 to pa = 295@xmath32 . there is also a radial gradient spanning the same range as the azimuthal gradient , with two distinct arcs at nearly identical slopes , and where the inner arc appears consistently older than the outer one . no correlation to the bar contact points is evident . * ngc 7716 ( fig . 5 t ) : thirty regions form a complete ring in this barred galaxy . no gradients or correlations to the bar are observed . * ngc 7742 ( fig . 5u ) : the circular and well resolved ring contains 38 regions . no gradients are observed . while many of the rings contain age gradients , a few show no gradient , namely ngc 613 , ngc 5905 , and ngc 5945 . this type of distribution is qualitatively more consistent with elmegreen s ( 1994 ) predictions , which suggest that the massive star formation in the nuclear ring is shocked into existence due to gravitational instabilities in the nuclear region around the ilrs . therefore , age gradients would not exist . comparisons of ew to age for these three rings also indicate that these starbursts are relatively older than those seen in the other rings , on the order of 10 myrs and higher . elmegreen ( 1997 ) suggests that these rings ( i.e. , with no gradient ) could last for as long as 100 myrs before sf ceases if the inflowing gas rate is high enough . the sfrs of these three rings ( 2@xmath26/yr , 2@xmath26/yr , and 4@xmath26/yr , respectively ; see section 6.2 and table 1 for sfr and inflow discussion ) are among the higher values in our sample but are consistent with other rates documented ( regan et al . 1997 ; jogee et al . . if we take into account that ngc 613 and ngc 5945 are partial rings in the optical , then the sfrs calculated here are lower limits . in this section we explore possible reasons for the result that only three galaxies show bi - polar age gradients around their rings , whereas many of the rings ( 9 of 22 ) show partial gradients along 25% - 30% of their rings , with the rest ( 10 of 22 ) showing no gradient . we find no apparent relationships between the presence or absence of age gradients and the morphology of the rings or their host galaxies . for example , whereas ngc 4321 , with its bi - polar age gradient , has a pair of well - defined dust lanes coming into the ring through the bar , ngc 1300 and ngc 5248 have similar dust lane morphologies yet show no gradients . some of the poorly resolved rings , such as those in ngc 4303 or ngc 5945 , do not show gradients , but given the presence of measured age gradients in the comparably small rings in ngc 6951 and ic 1438 , the lack of spatial resolution in the former two can not easily be used as an argument for the lack of a gradient . but even if we ignore galaxies with either small and badly resolved rings , or rings that do not have the classical aspect of dynamically - induced resonance rings ( ngc 613 and ngc 6503 are in the latter category ) , we are left with a significant number of rings in which we should have detected gradients if present , but which for some reason do not show any . this category includes , for instance , ngc 1300 , very similar to ngc 4314 or ngc 6951 which do show gradients ( all compact well - defined rings with around a dozen regions , sitting in strong bars with well - defined sets of dust lanes ) ; ngc 5248 , similar to ngc 4321 ( complex , rich rings with many regions organized into spiral arms fragments and hosted by a relatively weak bar ) ; ngc 7716 , similar to ngc 7217 which does have a gradient ; and ngc 7742 . for those rings that contain a gradient we also find no correlation between the presence of the gradient and direction of the ring rotation . in relating the location of the youngest regions to those of the contact points between the dust lanes and ring , we have been assuming that massive sf will follow very rapidly once the inflowing gas joins the ring . the appearance of a gradient in the ring may thus depend on whether or not material flowing in will immediately trigger gravitational collapse , and initiate massive sf . this in turn may be due to either a higher mass inflow rate ( or possibly increased clumpiness of the inflow ) and/or an overall higher existing gas density in the ring . each of these possibilities will ensure that soon after a clump of inflowing gas joins the ring , it will start to form massive stars . the alternatives , of low inflow rate and/or overall low gas density in the ring , might lead to a more gradual increase of the gas density , without necessarily leading to immediate gravitational collapse and massive sf on short timescales . in this case , the positions of the regions would bear no relation to the locations of the contact points . the ring would , in such a case , merely increase its gas density gradually , until at some stage , somewhere along the ring , an individual clump would become unstable to collapse ; therefore , no age gradients would ensue . to test this simple model , we must first consider the quantities mentioned above , gas inflow rate and gas density in the ring . these can in principle be determined from interferometric co measurements , but the process is not straightforward . the main issues are the conversion factor of @xmath34 to @xmath35 ( the @xmath36-factor ) , which may well not be equal to the canonical value in the kind of environments we consider here , and the determination of the fractions of detected molecular gas which are in fact flowing into the ring rather than around it ( as a consequence of a `` spray - type '' flow , see , e.g. , regan , vogel & teuben 1997 ; jogee et al . 2002 ) , or with the right physical conditions such as velocity dispersion and clumpiness to take part in the massive sf process . so although co interferometry has been presented for seven of our nuclear rings in the literature ( by regan , vogel & teuben 1997 ; sakamoto et al . 1999 ; jogee et al . 2002 , 2005 ; helfer et al . 2003 ; combes et al . 2004 ; garca - burillo et al . 2005 ) , we will not attempt here to derive the gas inflow rate and gas density in the ring from this collection of data , all with different observational characteristics . for two of our rings , ngc 1530 and ngc 5248 , gas inflow rates have been explicitly determined in the literature . for the former galaxy , regan et al . ( 1997 ) give a value of @xmath37 , whereas jogee et al . ( 2002 ) determine a value of `` a few''@xmath38 for the latter galaxy . considering the uncertainties in these values , we can say little more than that they are consistent with the sfrs determined for our nuclear rings ( see discussion below , and values in table 1 ) . we could assume that the sfr of the ring can act as a tracer of the inflow rate , although that would imply assuming , for instance , that inflowing gas is transformed into massive stars on very short timescales . if we do this , we would expect the age gradients to occur in those galaxies with the higher sfrs , which would be representative of higher gas inflow rates . in contrast , lower sfrs would indicate a low inflow rate so that the gas will gradually fill the ring , leading to sf only if and when the local gas density leads to gravitational collapse . this will occur essentially at random and thus result in a ring with no gradients . kennicutt ( 1998 ) derives a relation between the @xmath0 ionizing flux and the sfr for normal disk star forming galaxies , where the conversion factor is computed using stellar population synthesis modeling . since only stars with masses larger than 10@xmath26 and lifetimes less than 20@xmath25 dominate the integrated ionizing flux , the @xmath0 emission line provides a nearly instantaneous and linear measure of the sfr , independent of the previous star formation history . for solar abundances and our adopted imf ( @xmath39 ; @xmath28 and @xmath29 ) , we can use kennicutt s ( 1998 ) equation : @xmath40 to compute sfrs integrated over the entire ring , which are given in column 10 of table 1 . variable extinction certainly adds uncertainty in the computation of the sfr for circumnuclear regions . from the @xmath41 images , the patchiness of the extinction is very clear in several of our galaxies ( e.g. , ngc 473 , ngc 613 , ngc 1530 , ngc 5945 ) , which reveal only partial rings in @xmath0 . the less obscured regions will contribute more heavily to the line fluxes in these cases . the @xmath41 images clearly indicate that while the dust lanes can be traced nicely in the bar inmost cases ( where there is little star formation ) , the appearance of the nuclear rings is dominated by blue star - forming regions . this type of morphology makes it difficult to precisely model the effect of the dust , but attempts have been made for nuclear regions in particular . osmer , smith , & weedman ( 1974 ) analyzed six galaxies and derived integrated extinction values across the entire circumnuclear region ranging from @xmath42 mag , while hummel , van der hulst & keel ( 1987 ) found an extinction of @xmath43 in the central region of ngc 1097 . kennicutt ( 1998 ) acknowledges the high uncertainty and estimates that the errors in the sfr can be as high as @xmath1950% . a high - resolution survey paper by phillips ( 1996 ) for nine circumnuclear regions confirms the potential for high uncertainty values . following kennicutt , he finds that the sfrs vary by as much as a factor of ten when applying extinctions of @xmath44=1.1 and @xmath44=3.4 mag . he concludes that circumnuclear sf can be a dominant factor to the overall rates of such galaxies . we thus place the same caution that our sfrs contain potentially high uncertainties due to variable extinction throughout the nuclear rings . although there are possible large uncertainties in the sfr due to extinction , using the sfr can provide a possible link to an explanation for the existence of age gradients , via the gas inflow rate . figure 9 plots the integrated sfr over the entire ring for all galaxies and distinguishes those rings that show a gradient and those that do not . there is no obvious correlation between the sfr and the appearance of a gradient , although we can not exclude that such a connection does exist but is obscured by high dust extinction . the average mean for those without gradients ( @xmath45 , where the uncertainty is the standard error ) is slightly larger for those with a gradient ( @xmath46 ) , but given the large mean deviations , we can not distinguish in a statistical sense between the two cases . this could be due to several factors . all of the gradients , except for those in ngc 1343 and ngc 4321 , are partial gradients . that is , their gradient does not range continually from one contact point to the next . ngc 1343 and ngc 4321 , which represent the``ideal '' scenario , do have high sfrs ( @xmath47 for both cases ) when compared to the rest of the sample . computing the average sfr of the ring also is insensitive to the steepness of the gradient , the size of the ring , the size of the individual regions , or the patchiness of the ring , which all add complexity to the interpretation of the data . from our analysis of age gradients we thus conclude that although age gradients along the ring are detected in more than half of the rings , all other rings show random variations of region ew , and thus age , with azimuth . we can not pinpoint any morphological parameters that might distinguish the host galaxies and bars of those rings with from those without gradients . another strong conclusion from our analysis is that the kind of clear bi - polar age gradient seen before in ngc 4321 ( ryder , knapen , & takamiya 2001 ; allard et al . 2006 ) is rare - we only see a similar bi - polar gradient in one more galaxy , ngc 1343 . it is not clear why these two galaxies show their gradients , whereas other galaxies with very similar bar - ring systems show gradients that are not bi - polar , or no gradients at all . it is agreed that the presence of a galactic bar can have significant influence on angular momentum and re - distribution of gas , including inflow towards the central regions ( e.g. , combes & gerin 1985 ; athanassoula 1992 , 2000 ; knapen et al . 1995a ; heller & shlosman 1996 ; maciejewski et al . 2002 ) . observed kinematics reveal that the shock - induced flows move gas radially inwards along the bar dust lanes and tend to collect at the intersection of the dust lanes with the ring . these contact points are thought to be approximately perpendicular ( within the plane of the disk ) to the pa of the bar major axis ( regan & teuben 2003 ) but have been seen to lead the bar by as little as 60@xmath31 in numerical models ( heller & shlosman 1996 ) . the pile up of gas at these two points in the ring can be expected to spark sf . therefore , one could predict to find the youngest stellar regions in the ring near the contact points . for the barred spiral galaxies in our sample , we compare the location of the youngest regions in the ring to the derived location of the contact points . we first identified the youngest region in each hemisphere , where the hemispheres are separated by the bar pa . taking into account the direction of flow around the ring ( from our @xmath48 images ) , we calculate the pa offset between the region and the contact points . table 2 shows the pas of both the contact point and the youngest region in each hemisphere , along with the directional flow of the ring . we find that in two - thirds of the galaxies , one of the bar contact points is aligned with the youngest region in the associated hemisphere within 20@xmath32 of the contact point . two galaxies , ngc 4314 and ngc 5248 , have the youngest region in both hemispheres aligned with the contact points . our results for both of these rings are consistent with those of benedict et al . ( 2002 ) and maoz et al . ( 2001 ) , respectively , who also find that the youngest stars were located at the contact points . figure 10 shows a histogram of the distribution of the angular offsets between the bar major axis and the locations of the two youngest hii regions in each ring . a peak in frequency around the contact point locations is seen . we next calculate the times from the bar major axis pa to the location of the contact points with those of the youngest region in each hemisphere , assuming we azimuthally move in the direction of ring flow . we compute the period of the rings using measurements of the ring radius and the rotational velocity at the ring radius . we chose the major axis length of each ring as derived from ellipse ( see section 3 and table 1 ) , and obtained the rotational velocity values from the literature and from our own densepak ifu data taken in 2003 & 2004 ( l. m. mazzuca et al . 2006 , in prep . ) . table 3 shows the major axis ring radius , the adopted rotational velocity along with its reference , and the period for each ring . since we predict the contact points to be @xmath690@xmath32 from the bar major axis , we can compute their location with respect to the bar pa in each hemisphere , and thus calculate the amount of time it would take to travel to that location . we compare this travel time to that associated with the location of the youngest region in each hemisphere . overall , the expected travel times to the contact points coincide with the times computed from the bar pa to the youngest regions , which further strengthens the theory that the youngest regions are located near the contact points . we find only one region , in ngc 1530 , that deviates from the general trend . in this case , the youngest region in one of the hemispheres is more aligned with the pa of the ring than that of the bar . the analysis described above considers merely the rotational velocity of the gas in the ring region while deriving travel times . there is an additional contribution from the bar , which rotates with a certain bar pattern speed ( assuming that the ring co - rotates with the bar ) . estimating the relative contributions of these two rotation components , we consider parameters for a typical ring in our sample ( see table 1 ) of @xmath49kpc , @xmath50kms@xmath51kpc@xmath51 , and @xmath52,kms@xmath51 , which yields a ratio of the contributions of circular to bar pattern speeds into the velocities around the ring of @xmath53 . given that the rotational velocity is dominant , that the uncertainties in determining the bar pattern speed ( and , in fact , the direction of bar rotation ) are significant ( see elmegreen 1996 and knapen 1999 for reviews ) , and that the uncertainties from other sources , as described above , in the determination of travel times around the ring are already rather large , we have not pursued to derive bar pattern speeds and incorporate them into our analysis .

we use population synthesis models to estimate ages of each-emitting ( hii ) region , which range from 1 myr to 10 myrs throughout the rings . we find that approximately half of the rings contain azimuthal age gradients that encompass at least 25 of the ring , although there is no apparent relationship between the presence or absence of age gradients and the morphology of the rings or their host galaxies . ngc 1343 , ngc 1530 , and ngc 4321 show clear bipolar age gradients , where the youngest regions are located near the two contact points of the bar and ring . we speculate in these cases that the gradients are related to an increased mass inflow rate and/or an overall higher gas density in the ring , which would allow for massive star formation to occur on short timescales , after which the galactic rotation would transport the regions around the ring as they age . two - thirds of the barred galaxies show correlation between the locations of the youngest region(s ) in the ring and the location of the contact points , which is consistent with predictions from numerical modeling .

we present results from a photometric survey of 22 nuclear rings , aiming to provide insight into their star formation properties , including age distribution , dynamical timescales , star formation rates , and galactic bar influence . we find a clear relationship between the position angles and ellipticities of the rings and those of their host galaxies , which indicates the rings are in the same plane as the disk and circular . we use population synthesis models to estimate ages of each-emitting ( hii ) region , which range from 1 myr to 10 myrs throughout the rings . we find that approximately half of the rings contain azimuthal age gradients that encompass at least 25 of the ring , although there is no apparent relationship between the presence or absence of age gradients and the morphology of the rings or their host galaxies . ngc 1343 , ngc 1530 , and ngc 4321 show clear bipolar age gradients , where the youngest regions are located near the two contact points of the bar and ring . we speculate in these cases that the gradients are related to an increased mass inflow rate and/or an overall higher gas density in the ring , which would allow for massive star formation to occur on short timescales , after which the galactic rotation would transport the regions around the ring as they age . two - thirds of the barred galaxies show correlation between the locations of the youngest region(s ) in the ring and the location of the contact points , which is consistent with predictions from numerical modeling .

1503.08205

i

early _ chandra _ and _ xmm - newton _ x - ray observations revealed that the amount of gas cooling to very low temperatures at the centers of cool core clusters is much less than what is expected from simple radiative cooling models ( david et al . 2001 ; peterson et al . 2001 ; peterson & fabian 2006 ) . the implication is that the diffuse x - ray emitting gas must be heated , either by pre - heating during cluster formation or by ongoing energy injection . the most likely heating mechanism is feedback due to energy injection by the central active galactic nucleus ( agn ) of the cd galaxy ( see mcnamara & nulsen 2007 and fabian 2012 for recent reviews ) . during this process , matter is accreted onto the central supermassive black hole ( smbh ) , which drives powerful jets . these jets evacuate cavities in the intracluster medium ( icm ) , which can drive shocks as they are inflated and subsequently rise buoyantly ( churazov et al . the energy contained in cavities and shocks is then available to heat the icm , which lowers the cooling rate of the gas and subsequently the smbh accretion rate . the ensuing decrease in agn heating allows the gas to once again cool and accrete onto the smbh , establishing a feedback loop that regulates the temperature of the icm . several studies have shown that , generally , the total enthalpy in cavities in cool core systems is sufficient to offset radiative cooling in individual galaxies , galaxy groups , and clusters ( brzan et al . 2004 ; rafferty et al . 2006 ; nulsen et al . 2007 ; hlavacek - larrondo et al . 2012 ) . however , the details of how and where this energy gets transferred to the icm are unclear . weak agn outburst shocks are also expected to heat the icm , although they are difficult to detect and clear examples are very rare . galaxy groups provide an excellent opportunity to study agn feedback . their lower temperatures are more easily measured with modern high angular resolution x - ray satellites , and their central agn can more easily disturb the diffuse gas due to their shallower gravitational potentials as compared with clusters . here we report on results from a very deep _ chandra _ observation of the central galaxy in the galaxy group ngc 5813 ( n5813 ) . this group is a relatively isolated sub - group in the ngc 5846 group ( mahdavi et al . 2005 ; machacek et al . 2011 ) . in randall et al . ( 2011 , hereafter r11 ) we presented results based on an initial 150 ks _ chandra _ observation of n5813 . the icm in this group has a remarkably regular morphology , with three pairs of roughly collinear cavities and associated surface brightness edges , and shows no clear signs of a recent merger event . ( note that we refer to the diffuse gas in this group as the icm rather than the intragroup medium ( igm ) throughout to stress the connection with feedback in clusters and to avoid confusion with the intergalactic medium . ) with clear , cleanly separated signatures from three distinct outbursts of the central agn and no other significant dynamical processes at work , n5813 is uniquely well - suited to the study of agn feedback . in this work , we focus on the implications for agn feedback and the outburst history of the central smbh . we assume an angular diameter distance to n5813 of 32.2 mpc ( tonry et al . 2001 ) , which gives a scale of 0.15 kpc/. all uncertainty ranges are 68% confidence intervals ( i.e. , 1@xmath5 ) , unless otherwise stated .

we present results from a very deep ( 650 ks ) _ chandra _ x - ray observation of the galaxy group ngc 5813 , the deepest _ chandra _ observation of a galaxy group to date . this system is therefore unique in exhibiting three cavity pairs , each associated with an unambiguous shock front , arising from three distinct outbursts of the central agn . as such , it is particularly well - suited to the study of ongoing agn feedback .

we present results from a very deep ( 650 ks ) _ chandra _ x - ray observation of the galaxy group ngc 5813 , the deepest _ chandra _ observation of a galaxy group to date . earlier observations showed two pairs of cavities distributed roughly collinearly , with each pair associated with an elliptical shock front . the new observations confirm a third pair of outer cavities , collinear with the other pairs , and reveal an associated outer outburst shock , with measured temperature jump , at kpc . this system is therefore unique in exhibiting three cavity pairs , each associated with an unambiguous shock front , arising from three distinct outbursts of the central agn . as such , it is particularly well - suited to the study of ongoing agn feedback . the implied mean kinetic power is roughly the same for each outburst , demonstrating that the average agn kinetic luminosity can remain stable over long timescales ( myr ) . the two older outbursts have larger , roughly equal total energies as compared with the youngest outburst , implying that the youngest outburst is ongoing . we find that the radiative cooling rate and the mean shock heating rate of the gas are well balanced at each shock front , suggesting that agn outburst shock heating alone is sufficient to offset cooling and establish agn / icm feedback within at least the central 30 kpc . this heating takes place roughly isotropically and most strongly at small radii , as is required for feedback to operate . we suggest that shock heating may play a significant role in agn feedback at smaller radii in other systems , where weak shocks are more difficult to detect . we find non - zero shock front widths that are too large to be explained by particle diffusion . instead , all measured widths are consistent with shock broadening due to propagation through a turbulent icm with a mean turbulent speed of . finally , we place lower limits on the temperature of any volume - filling thermal gas within the cavities that would balance the internal cavity pressure with the external icm . the most stringent limit we find is kev .

1503.08205

c

shocks are expected to heat the icm as they propagate . while there is a relatively large temperature jump at the shock front , this increase is transient as the gas subsequently expands and cools . the relevant quantity for lasting heating of the gas is the change in entropy . the equivalent amount of heat energy @xmath27 imparted to the gas by a shock due to a change in entropy @xmath28 is given by @xmath29 where @xmath30 is the total thermal energy of the gas , @xmath31 is the adiabatic index ( taken to be 5/3 ) , and @xmath32 and @xmath33 are the pressure and density , respectively . thus , each shock contributes a fraction @xmath34 of the total thermal energy in the gas . in the case of weak shocks , this fraction is small ( between 0.412% for the shocks we detect in n5813 ) . to compare with radiative cooling , we are interested in the cumulative effect of shock heating per local cooling time in the gas ( i.e. , the number of shocks per local cooling time and the total amount of heat energy deposited in the gas ) . we approximate the local cooling time just outside each shock edge as the time it would take the gas to radiate away all of its thermal energy based on its deprojected emissivity . based on the shock ages given in table [ tab : shocks ] , and keeping in mind that these ages are expected to be underestimates for young shocks and overestimates for older shocks , we assume an outburst repetition rate of one every 20 myr . the results from the above comparison of the shock heating and radiative cooling rates are summarized in table [ tab : heating ] . given the various statistical and systematic uncertainties associated with , e.g. , the shock mach numbers , the shock ages and outburst repetition rate , the deprojected cooling luminosity , etc . , these numbers should be considered to be rough estimates . nevertheless , there is good agreement between the number of shocks expected per cooling time ( column 3 ) and the number required to completely offset radiative cooling ( column 4 ) . we conclude that shock heating alone is sufficient to balance radiative cooling in the gas out to at least @xmath230 kpc . this extends our earlier result in r11 , where we found a balance between heating and cooling out to @xmath210 kpc . at 30 kpc , the cooling time ( @xmath35 gyr ) is approaching the expected age of the system , indicating that there is no need for additional heating beyond this radius to completely balance cooling and explain the lack of a strong cooling flow in this system . we can estimate the average cavity power @xmath36 by dividing the total enthalpy of the cavities ( estimated as @xmath37 for each cavity , for a total of @xmath38 @xmath39 ) by the age of the oldest cavity pair ( @xmath40 yr ; see r11 , table 3 ) . this gives @xmath41 @xmath39 . spectral fitting gives a total x - ray luminosity of @xmath42 @xmath39 within a radius enclosing all of the cavities ( @xmath43 kpc ) . thus , in n5813 we find that a few times the @xmath44 work required to inflate the cavities is in principle large enough to offset radiative cooling , as has generally been found in other systems ( e.g. , brzan et al . 2004 ; rafferty et al . 2006 ; nulsen et al . 2007 ; hlavacek - larrondo et al . 2012 ) . since we have shown that , in n5813 , shock heating alone is sufficient to balance cooling , one might ask whether the total heating from cavities and shocks leads to an `` overheating '' of the icm , breaking the balance between heating and cooling that is required for agn feedback to operate over long time scales . although cavities are expected to deposit some of their enthalpy in the icm as they rise buoyantly ( mcnamara & nulsen 2007 ) , this heating is not directly observed , and the details on how and where cavities heat the icm are poorly understood . furthermore , cavities can only directly heat the icm locally , as they rise radially , whereas roughly isotropic heating must take place close to the central agn to regulate feedback . mixing may help to distribute locally heated gas ( e.g. , zhuravleva et al . 2014 ) , although the gas motions must be small enough to not completely destroy the observed x - ray cavities . shocks , in contrast , heat the gas roughly isotropically and most strongly at smaller radii , and the thermal effect of shocks on the icm is , in some cases , directly observed . we suggest that agn outburst shocks may generally play a significant role in agn feedback , particularly at small radii where the mach numbers are higher . the cavities are then free to rise buoyantly , and release their energy to heat the icm at larger radii . the fact that cavities are observed at larger radii demonstrates that they do not necessarily release their enthalpy to the icm at small radii , consistent with this picture . weak shocks are generally difficult to detect , since the shock fronts are thin and easily masked by projection effects . they are more easily detected in n5813 due to its proximity , low gas temperature , and regular morphology . the fact that one of the handful of examples of confirmed outburst shocks known in clusters , in abell 2052 ( blanton et al . 2011 ) , was confirmed by a measured temperature jump only after very deep _ chandra _ observations and careful deprojection is consistent with this scenario . similarly , no temperature jump is found associated with the presumed outburst shock in the perseus cluster using extremely deep _ chandra _ observations , even though it is the x - ray brightest cluster ( graham et al . 2008 ) . measurements of the cavities and shocks allow us to estimate the total mechanical outburst energy for each of the three outbursts in n5813 . since the mechanical luminosity dominates the total agn energy output in n5813 ( r11 ) , as is generally the case for kinetic mode agn feedback ( fabian 2012 ) , this gives us information on the total outburst energy history of the agn . we take the cavity internal energy to be @xmath45 , where the pressure @xmath32 is taken from the azimuthally averaged pressure profile . the assumed cavity dimensions and derived internal energies are given in table [ tab : cavities ] . we use the cavity internal energy rather than the enthalpy ( which is the sum of the internal energy and the work required to inflate the cavity , and roughly equal to @xmath37 for cavities filled with relativistic particles ) since the work done during cavity expansion goes into driving shocks , the energy of which we account for separately . as in r11 , we estimate the outburst energy in shocks as @xmath46 where @xmath47 and @xmath48 are the pre- and post - shock pressures , respectively , and @xmath49 is the total volume enclosed by each roughly ellipsoidal shock surface . although equation [ eq : eshock ] is expected to slightly underestimate the shock energy as the mach numbers were larger at earlier times ( giving larger pressure jumps ) , in r11 we showed that this estimate agrees well with shock energies derived from simple 1d hydrodynamic simulations of a central point explosion by matching the simulated surface brightness profiles with the observations . the total mechanical energy output of each outburst is simply the sum of the total cavity and shock energies . we note that the ratio of the energy in cavities to that in shocks is between 0.150.3 for each outburst , and that in the case of the central outburst , where the cavities occupy a significant fraction of the volume enclosed by the 1 kpc shock surface , this ratio is somewhat lower than the expected value of @xmath50 . this is likely a result of underestimating the central gas pressure , and hence the central cavity energies , due to the complicated morphology in this region , which leads to systematic uncertainties associated with projection effects and a lack of knowledge on the volume filling factor of the x - ray emitting gas . however , we note that such an underestimate would only moderately affect our total outburst energy , well within the factor of a few at which we expect our simple estimates to be accurate , and hence would not affect our main conclusions . using the above estimates , we find total outburst energies of @xmath51 erg , @xmath52 erg , and @xmath53 erg for the outbursts associated with the 1 kpc , 10 kpc , and 30 kpc shocks , respectively . as in r11 , we find the outburst energy of the 1 kpc outburst to be more than a factor of ten less than that of the 10 kpc outburst . based on this , we concluded that either the 1 kpc outburst is ongoing , with the agn actively inflating the cavities , or that the mean jet power varies significantly over timescales on the order of 10 myr . here , we find remarkable agreement between the total outburst energies of the 10 kpc and 30 kpc outbursts . this suggests that the mean outburst ( or jet ) power , averaged over the outburst interval of a few 10 myr , is fairly stable , and that the total energy of the 1 kpc outburst is lower because this outburst is ongoing . in r11 , we estimated the outburst power as the total energy divided by the age of the outburst . here , we instead estimate this power as the total energy divided by the duration of each outburst , which we take to be the shock age for the youngest outburst ( table [ tab : shocks ] ) and the outburst interval ( @xmath54 myr , [ sec : feedback ] ) for the remaining outbursts . this gives mean outburst powers of @xmath55 @xmath39 , @xmath56 @xmath39 , and @xmath57 @xmath39 for the 1 kpc , 10 kpc , and 30 kpc outbursts , respectively . thus , we find the mean outburst power is indeed roughly constant , certainly within a factor of a few , which is the level at which we expect our rough estimates to be accurate . we note that in r11 we found a lower power for the 1 kpc outburst . this difference arises mainly from using results from our numerical model in r11 , which predicts a lower shock energy and larger shock age as compared with the estimates based on observations alone ( see table 2 in r11 ) . the source of this difference is likely to be a systematic error that arises when applying the spherically symmetric model to the 1 kpc shock , which clearly has a more complicated morphology ( see figures [ fig : core_ximg ] & [ fig : core_tmap ] ) . we stress that our result on the consistency of the outburst power only applies to the mean power averaged over the outburst interval of a few 10 myr . agn luminosities are known to vary by up to several orders of magnitude over very short ( observable ) timescales ( e.g. , harris et al.2009 ) . however , in principle the outburst signatures in n5813 could be created with a constant jet power . in this case , the cavities expand rapidly and drive shocks just after they are formed . the expansion rate drops as the _ fractional _ energy input rate decreases , and the shocks separate from the cavities and propagate outwards . as the cavities rise buoyantly , they eventually disconnect from the central jets ( once the buoyant speed exceeds the expansion rate ) , which then begin inflating a new pair of cavities and the process repeats ( similar models are discussed , e.g. , in fabian et al.2003 ) . therefore , we use the term `` outburst '' to refer to the creation of a cavity pair and its associated shock , rather than a rapid increase in jet power , since these features are consistent with a kinetic jet power that either also cycles in outbursts or is roughly constant . we conclude that the most likely scenario is that n5813 is in a `` steady state '' kinetic feedback mode , with the agn outbursts roughly equally spaced in time , and each outburst depositing a similar amount of total energy into the icm , such that the mean agn outburst power is roughly constant . the lower total power of the 1 kpc outburst is an indication that this outburst is ongoing , and has yet to deposit the bulk of its energy in the icm . the detection of 1.4 ghz radio emission filling the inner cavities ( from young , high - energy , non - thermal particles injected by the agn ) , along with shock heated cavity rims that have not yet separated from the cavities ( as they have clearly done for the intermediate and outer cavities ) , are consistent with this interpretation ( r11 ) . this is also consistent with results from allen et al . ( 2006 ) , who find evidence for accretion flows around central agn that are stable over a few million years . the fact that n5813 shows little evidence of a recent merger or other complicated icm `` weather '' , probably contributes to it being able to maintain such steady state feedback over long timescales . fits to the surface brightness profiles across the shock fronts reveal that the se and nw 10 kpc fronts have non - zero widths that can not be explained by _ chandra s _ psf ( [ sec : shock_structure ] ) . measurements of the widths of surface brightness edges in cluster x - ray observations have been used to place constraints on transport processes in the icm by comparing these widths with the local collisional mean free paths of the particles . edges that are significantly narrower than the particle mean free path indicate that coulomb diffusion is suppressed across the edge . in the case of cold fronts in clusters , the front widths are found to be significantly smaller than the particle mean free paths ( e.g. , vikhlinin et al . 2001a ; russell et al . 2012 ) , implying that coulomb diffusion is suppressed across the fronts . however , in cold fronts the suppression of transport processes ( and kelvin helmholtz instabilities ) is likely due to magnetic draping , where magnetic field lines are stretched along the cold front edge as the relatively cool , dense gas moves through the icm ( vikhlinin et al . 2001b ; asai et al . 2004 , 2005 , 2007 ; lyutikov 2006 ; dursi & pfrommer 2008 , zuhone et al.2011 ) . in this case we consider shock fronts which propagate through the icm , and therefore magnetic draping is not expected to occur . in the case of merger shocks , markevitch & vikhlinin ( 2007 ) find a bow shock width of roughly 35 kpc , on the order of the local particle mean free path , for 1e 0657 - 56 ( the bullet cluster ) , although this width is only marginally preferred over a zero width front . russell et al . ( 2012 ) examine shock widths in the merging cluster abell 2146 , which contains a leading bow shock and a trailing reverse shock . they find finite width shocks in each case , with the reverse shock width being significantly smaller , and the bow shock width being marginally smaller , than the particle mean free path . they conclude that transport processes are suppressed across these merger shocks . in the case of agn outburst shocks , croston et al . ( 2009 ) consider the thickness of the northeastern shock in centaurus a , but their results are inconclusive . it is therefore of interest to compare our measured shock widths with the coulomb mean free path of particles in the icm . in the region of the shock fronts there are four relevant mean free paths : that in the pre - shock region , @xmath58 , that in the post - shock region , @xmath59 , that of particles crossing the front from the post - shock to the pre - shock region , @xmath60 , and that of particles crossing the front from the pre - shock region to the post - shock region , @xmath61 . in our case , the largest and most relevant mean free path is @xmath62 , which is given by @xmath63 where @xmath64 is the pre - shock electron density , @xmath65 , @xmath66 is the post - shock gas temperature , @xmath67 is the pre - shock gas temperature , @xmath68/2y^2 $ ] , and @xmath69 is the error function ( spitzer 1962 ) . when calculating @xmath60 , pre - shock temperatures were taken from the projected temperature profiles just outside the shock fronts . post - shock temperatures were calculated from the pre - shock temperatures by applying the rankine - hugoniot jump conditions , rather than taken from the observed projected post - shock temperatures . we note that this is a conservative assumption from the perspective of finding a mean free path that is smaller than the shock width , as it gives a higher post - shock temperature ( that is not diminished by projection effects ) , which gives a larger value for @xmath60 . the relevant particle mean free path is given for each shock front in table [ tab : shocks ] . the uncertainty in the mean free path is dominated by the uncertainty in the pre - shock temperature , which is on the order of 10% , leading to a mean free path uncertainty of roughly 20% . in all cases , the particle mean free path is significantly smaller than the shock width , on the order of ten times smaller than the 90% confidence lower limit for the 1 kpc and 10 kpc shocks ( where lower limits on the shock widths can be placed ) . for a weak shock , the shock width is expected to be roughly @xmath70 , where @xmath71 is the effective particle mean free path ( landau & lifshitz 1987 ; mcnamara & nulsen 2007 ) , or 1.42 times @xmath71 for the weak shocks we consider here . thus , the apparent shock widths are too large to be explained by particle diffusion alone . we note that this result likely precludes using these shock fronts to place accurate constraints on the electron - ion equilibration timescale , as has been done , e.g. , by russell et al . ( 2012 ) . as noted in [ sec : shock_structure ] , a measured finite shock width may arise due to deformations in and broadening of a shock front as it propagates through a `` clumpy '' and/or turbulent icm . nulsen et al . ( 2013 ) provide an estimate of the expected shock width due to turbulence as a function of radius as the shock propagates through a uniformly turbulent icm . the shock width ( @xmath72 , defined as the rms of the displacement of sections of the shock front due to turbulence ) is determined by the distance traveled ( @xmath73 ) , the shock speed @xmath74 , the coherence length of the turbulence ( @xmath75 ) , and the rms turbulent speed ( @xmath76 ) . here , we can invert this relation to find the turbulent speed implied by the observed shock width : @xmath77 the rms turbulent speed implied by measurements of each shock front we consider are given in table [ tab : shocks ] . following nulsen et al . ( 2013 ) , we take the coherence length to be @xmath78 ( rebusco et al . remarkably , the implied turbulent speed is consistent with roughly 70 @xmath3 in each case . we note that , in principle , the turbulent speeds calculated here are upper limits on the true icm turbulence , as this calculation does not include the contribution of density inhomogeneities to shock broadening , projection effects , and the effects of an irregular shock front geometry ( which is approximated as spherically symmetric in sectors ) , all of which will act to increase the apparent shock width . however , as the calculation is only approximate , our results should not be taken as hard upper limits . the implied turbulent velocity of roughly 70 @xmath3 is reasonable compared with results from simulations ( 100300 @xmath3 ; lau et al . 2009 ) and observations ( e.g. , de plaa et al . 2012 ; sanders & fabian 2013 ; zhuravleva et al . while this value is on the low end of the reported range , we note that n5813 is a relatively isolated galaxy group ( r11 ) , which has a regular morphology and shows no signs of a recent major merger . thus , the level of merger - driven turbulence is expected to be low . additionally , we note that observational measurements will naturally be biased towards detecting systems with larger turbulent velocities . in several cases only upper limits can be placed , with all reported upper limits significantly larger ( a few to several 100 @xmath3 ) than the @xmath79 @xmath3 detection we report here ( sanders et al . 2011 ; bulbul et al . 2012b ; sanders & fabian 2013 ) . finally , this value is consistent with the range of turbulent velocities of 43140 @xmath3 recently reported by zhuravleva et al . ( 2014 ) for the ( relatively low mass ) virgo cluster . by considering the effects of resonant scattering on line ratios , de plaa et al . ( 2012 ) constrain the turbulent velocity in n5813 to be @xmath80 , significantly larger than our value of 70 @xmath3 . however , we do not view this as a serious discrepancy for several reasons . first , as mentioned above , the limits provided by equation [ eq : vturb ] are expected to be rough estimates . in particular , the coherence length @xmath75 is unknown and the only hard constraint is that @xmath81 . second , as noted by the authors themselves , the atomic data used to calculate the line ratios in de plaa et al . ( 2012 ) suffer from significant systematic uncertainty . for example , by comparing results derived with the spex code versus atomdb , they find inferred turbulent velocities for n5813 that differ by almost a factor of two . finally , we note that there are plausible physical origins for the higher level of turbulence found by de plaa et al . for example , they place constraints for the central @xmath82 kpc only , where the turbulent velocity may be larger than the total icm average due to the influence of the agn , whereas the estimates given here are averages over the entire region interior to each shock . the trend of the inferred turbulent speed decreasing with radius ( table [ tab : shocks ] ) , although not statistically significant , is consistent with this picture . it is interesting to note that the turbulent velocity inferred from the width of the central @xmath83 kpc shock is consistent with the range given by de plaa et al.(2012 ) , although , as noted above , the errors are large and the effects of the larger relative psf are unclear . additionally , we note that the resonant line ratio may also be affected by bulk flows in the icm ( e.g. , the radial gas flows behind the shock fronts ) , possibly leading to an over - estimate of the turbulence . we conclude that , while the measured shock widths are too large to be explained by coulomb diffusion , they are consistent with arising from the shocks propagating through a turbulent icm . the implied ratio of turbulent to thermal pressure support , estimated as the ratio of the turbulent energy to the thermal energy ( de plaa et al . 2012 ) , is on the order of a few percent ( @xmath84 ) for a turbulent speed of 70 @xmath3 . for each shock we consider , the local thermal diffusion coefficient @xmath85 , where @xmath86 is the sound speed , is significantly smaller ( by up to an order of magnitude ) than the implied turbulent diffusion coefficient @xmath87 . thus , turbulent diffusion dominates the microscopic transport in the icm ( at least in this case , and likely in other similar - size groups , which are expected to have similar bulk icm properties ) . although the x - ray cavities must be close to pressure equilibrium with their surroundings , radio observations show that generally the pressure support from relativistic non - thermal electrons , under the assumption of equipartition , is insufficient to balance the thermal pressure in the icm ( brzan et al . . additional pressure support might be provided by heavy non - thermal particles , or by high temperature thermal gas , with deep x - ray observations providing constraints on the contribution from the latter ( e.g. , schmidt et al . 2002 ; blanton et al . 2003 ; sanders & fabian ( 2007 ) ; rafferty et al . ( 2013 ) ) . here we place similar limits for the low mass galaxy group n5813 . to place lower limits on the temperature of thermal gas in the cavities we use a method similar to that employed in previous studies of other systems ( e.g. , sanders & fabian 2007 ; rafferty et al . 2013 ) . due to the complex thermal structure of the gas , we do not use comparison regions outside of the cavities as in sanders & fabian ( 2007 ) . rather , we place limits based on fits to spectra extracted from regions at the cavity centers , where the contrast is highest and the relative contribution from high temperature gas inside the cavities is expected to be the largest . each spectrum is fit with two absorbed apec model components . the first component models the contribution from the total projected emission , while the second models hotter thermal emission from within the cavities . to derive conservative estimates , the temperature , abundance , and normalization of the first component are allowed to vary . we find that within the cavity regions this single thermal component is sufficient to adequately model the total projected emission ( additional thermal components do not significantly improve the fits and are not well constrained ) . for the second component , the temperature is fixed at some value , the abundance is tied to that of the first component , and the normalization is allowed to vary . for an assumed cavity volume , the upper limit on the normalization gives an upper limit on the density . if we further assume that the cavity is in pressure equilibrium with its surroundings , that the pressure is equal to the average azimuthal pressure at the cavity radius ( figure [ fig : azprof ] ) , and that the thermal gas dominates the pressure support inside the cavities , an upper limit on the volume filling fraction of the gas in the cavities ( for the given temperature ) is obtained . a lower limit on the gas temperature is obtained by increasing the fixed temperature of the hot gas until the upper limit on the volume filling fraction is equal to unity . we concentrate on the cavities with the largest contrast and the most regular morphology . since they are closely spaced ( and therefore in a similar environment ) we fit the inner cavities together , assuming a cylindrical geometry with a radius of @xmath88 ( 0.488 ) kpc and a depth of @xmath89 ( 0.815 ) kpc for the northeastern ( southwestern ) central cavity . for the intermediate cavities , only the southwestern cavity is considered ( with @xmath90 kpc , @xmath91 kpc ) as it has a larger contrast and more regular shape compared with the northeastern intermediate cavity , which may be split into two cavities and may be connected to the northeastern central cavity ( r11 ) . similarly , we choose the northeastern outer cavity over its southwestern counterpart due to its larger contrast and more regular shape , and assume an oblate spheroidal geometry with major axis @xmath92 kpc and minor axis @xmath93 kpc in the plane of the sky . we find limits on the temperature of any volume filling thermal gas in the cavities of @xmath94 kev , @xmath95 kev , and @xmath96 kev for the inner , intermediate , and outer cavities , respectively ( for comparison , the limit placed by rafferty et al.2013 from deep _ chandra _ observations of the galaxy group hcg 62 is 4.3 kev ) . our most stringent constraint of @xmath97 kev for the intermediate cavities implies a gas density in the cavities that is at least 20 times lower than the azimuthal average at that radius ( @xmath98 @xmath99 ) . we note that this method relies on several assumptions . for instance , the hot temperature component is assumed to arise solely from gas contained within the cavities ( it may be the case that hot thermal gas supplies only part of the pressure support , while , e.g. , heavy non - thermal particles or magnetic fields make up the difference ) . additionally , the azimuthally averaged pressure profile , which is used to estimate the mean external pressure at each cavity , is derived under the assumption of spherical symmetry ( [ sec : azprofs ] ) , which is clearly violated at some level for this system ( figure [ fig : ximg ] ) . furthermore , some assumptions about the cavity geometries ( or , more specifically , their volumes ) must be made to calculate densities and pressures . the largest source of error is likely from the latter assumption . we find that an assumed uncertainty in cavity volume of 20% leads to an uncertainty of @xmath100% on the temperature limit ( a similar result was found by rafferty et al . 2013 ) . the residual image shown in figure [ fig : ximg ] reveals a `` channel '' of decreased surface brightness to the north , apparently connected to the ne outer cavity . to test the significance of this feature , we extracted the surface brightness profile in azimuthal bins roughly 9 wide and 64 long across the channel . the profile , shown in figure [ fig : nchan ] , shows a clearly significant dip across the channel , indicating that this is a real feature . since the northern channel appears to connect to the ne outer cavity , one interesting possibility is that this channel is the result of energy ( presumably mostly in the form of non - thermal particles ) leaking through the bright cavity rim and heating the icm . indeed , the temperature maps shown in figure [ fig : tmap ] show relatively high temperatures in the region of the northern channel , although the correlation between the high temperature region in the temperature map and the channel in the residual map is not exact . although cavities are expected to heat the icm ( see [ sec : feedback ] ) , such a direct detection of this heating has not yet been observed . we therefore extracted temperatures both in ( wider ) azimuthal bins across the northern channel , and in identical elliptical regions within and to either side of the channel ( at roughly the same distance from the center ) . in neither case did we find a significant temperature enhancement associated with the channel , with temperatures of all regions agreeing within roughly 1-@xmath5 . we conclude that , although it is possible that the northern channel is a result of energy leaking from the ne cavity and heating the icm , causing the gas in this region to expand to pressure equilibrium ( and subsequently cool adiabatically ) and hence the density ( and surface brightness ) to drop , we find little evidence to support this interpretation . in particular , we can not rule out the possibility that this feature is simply due to large scale structure in the icm , e.g. , associated with previous mergers or bulk motion of the group , even in this relatively relaxed system . another possibility is that this deficit is a left over cavity from an even older , fourth outburst that lies off of the axis defined by the other three cavity pairs , although the fact that it is at least partially within the 30 kpc shock front is difficult to reconcile with this interpretation . deep , low - frequency radio observations would be useful to both detect the putative low - energy non - thermal particles in the ne outer cavity and to see if this emission extends out along the northern channel , consistent with it arising from a leaking cavity .

this heating takes place roughly isotropically and most strongly at small radii , as is required for feedback to operate . we suggest that shock heating may play a significant role in agn feedback at smaller radii in other systems , where weak shocks are more difficult to detect . we find non - zero shock front widths that are too large to be explained by particle diffusion .

we present results from a very deep ( 650 ks ) _ chandra _ x - ray observation of the galaxy group ngc 5813 , the deepest _ chandra _ observation of a galaxy group to date . earlier observations showed two pairs of cavities distributed roughly collinearly , with each pair associated with an elliptical shock front . the new observations confirm a third pair of outer cavities , collinear with the other pairs , and reveal an associated outer outburst shock , with measured temperature jump , at kpc . this system is therefore unique in exhibiting three cavity pairs , each associated with an unambiguous shock front , arising from three distinct outbursts of the central agn . as such , it is particularly well - suited to the study of ongoing agn feedback . the implied mean kinetic power is roughly the same for each outburst , demonstrating that the average agn kinetic luminosity can remain stable over long timescales ( myr ) . the two older outbursts have larger , roughly equal total energies as compared with the youngest outburst , implying that the youngest outburst is ongoing . we find that the radiative cooling rate and the mean shock heating rate of the gas are well balanced at each shock front , suggesting that agn outburst shock heating alone is sufficient to offset cooling and establish agn / icm feedback within at least the central 30 kpc . this heating takes place roughly isotropically and most strongly at small radii , as is required for feedback to operate . we suggest that shock heating may play a significant role in agn feedback at smaller radii in other systems , where weak shocks are more difficult to detect . we find non - zero shock front widths that are too large to be explained by particle diffusion . instead , all measured widths are consistent with shock broadening due to propagation through a turbulent icm with a mean turbulent speed of . finally , we place lower limits on the temperature of any volume - filling thermal gas within the cavities that would balance the internal cavity pressure with the external icm . the most stringent limit we find is kev .

1503.08205

i

we have presented results from our analysis of a very deep _ chandra _ observation of the galaxy group n5813 . this observation confirms an outer cavity pair and associated shock ( only hinted at in r11 ) , giving a total of three pairs of roughly collinear cavities , with each pair associated with an elliptical shock front with a measured temperature jump . the derived mach numbers are 1.8 , 1.5 , and 1.2 for the 1 kpc , 10 kpc , and 30 kpc shocks , respectively . these features are cleanly separated signatures from three distinct outbursts of the central agn . we compare the shock heating rate to the radiative cooling rate locally at each shock front , and find that the rates closely balance one another . this demonstrates that shock heating alone is sufficient to offset gas cooling and enable agn feedback to operate within at least the central 30 kpc ( compared with 10 kpc in r11 ) . we suggest that shock heating is likely important at small radii in other cool core clusters and groups , but that in most cases the shocks are more difficult to detect due to higher icm temperatures , larger distances , and more complicated icm structure , or `` weather '' , instigated by mergers . we find that the total outburst energies of the old and intermediate age outbursts are roughly equal , while the energy of the young outburst is more than a factor of 10 less . however , the mean powers of all of the outbursts are roughly the same , within a factor of two , indicating that the mean kinetic luminosity of the agn has remained stable for at least 50 myr . we suggest that the young outburst is ongoing , having deposited only a fraction of its total energy into the icm . the proximity of the central cavities to the agn , the relatively high - frequency radio emission that fills the cavities , and the shock heated rims surrounding the cavities ( that have not yet separated from the cavities , as is the case for the older outbursts ) are all consistent with this scenario . we find that the 10 kpc ( and possibly the 1 kpc ) elliptical shock front is broadened by @xmath101 kpc ( @xmath102 kpc ) , more than ten times the particle mean free path and thus too broad to be caused by particle diffusion . while we can not rule out broadening due to a clumpy icm and/or projection effects , using rough estimates we find that the measured shock widths ( which are upper limits for the 30 kpc shock ) are all consistent with broadening due to propagation through a turbulent icm with a turbulent speed of @xmath103 @xmath3 . this is within , but on the low end of , the range of turbulent speeds expected based on simulations and other observations , and thus provides a robust upper limit on the turbulence since other factors may contribute to the total shock broadening . this suggests that transport due to turbulence dominates that of particle diffusion throughout the icm in n5813 . using spectral fits in the cavity regions , we place lower limits on the temperature of any volume filling gas that could completely balance the pressure within the cavity with that in the external icm . our most stringent limit of @xmath104 kev comes from the intermediate cavity pair . finally , we find a channel of decreased surface brightness extending north from the outer ne cavity . we suggest that this feature may be due to energy leaking from the cavity and heating the icm , although we find no temperature enhancement in the channel to support this scenario .

earlier observations showed two pairs of cavities distributed roughly collinearly , with each pair associated with an elliptical shock front . the new observations confirm a third pair of outer cavities , collinear with the other pairs , and reveal an associated outer outburst shock , with measured temperature jump , at kpc . the implied mean kinetic power is roughly the same for each outburst , demonstrating that the average agn kinetic luminosity can remain stable over long timescales ( myr ) . instead , all measured widths are consistent with shock broadening due to propagation through a turbulent icm with a mean turbulent speed of . finally , we place lower limits on the temperature of any volume - filling thermal gas within the cavities that would balance the internal cavity pressure with the external icm .

we present results from a very deep ( 650 ks ) _ chandra _ x - ray observation of the galaxy group ngc 5813 , the deepest _ chandra _ observation of a galaxy group to date . earlier observations showed two pairs of cavities distributed roughly collinearly , with each pair associated with an elliptical shock front . the new observations confirm a third pair of outer cavities , collinear with the other pairs , and reveal an associated outer outburst shock , with measured temperature jump , at kpc . this system is therefore unique in exhibiting three cavity pairs , each associated with an unambiguous shock front , arising from three distinct outbursts of the central agn . as such , it is particularly well - suited to the study of ongoing agn feedback . the implied mean kinetic power is roughly the same for each outburst , demonstrating that the average agn kinetic luminosity can remain stable over long timescales ( myr ) . the two older outbursts have larger , roughly equal total energies as compared with the youngest outburst , implying that the youngest outburst is ongoing . we find that the radiative cooling rate and the mean shock heating rate of the gas are well balanced at each shock front , suggesting that agn outburst shock heating alone is sufficient to offset cooling and establish agn / icm feedback within at least the central 30 kpc . this heating takes place roughly isotropically and most strongly at small radii , as is required for feedback to operate . we suggest that shock heating may play a significant role in agn feedback at smaller radii in other systems , where weak shocks are more difficult to detect . we find non - zero shock front widths that are too large to be explained by particle diffusion . instead , all measured widths are consistent with shock broadening due to propagation through a turbulent icm with a mean turbulent speed of . finally , we place lower limits on the temperature of any volume - filling thermal gas within the cavities that would balance the internal cavity pressure with the external icm . the most stringent limit we find is kev .

astro-ph0405003

i

the orion nebula is one of the best studied star formation regions in the galaxy . the orion nebula cluster ( onc ) designates the inner 3 pc ( @xmath0 20 arcmin ) from @xmath1c orionis , and contains more than three thousand stars . the core of the onc , also known as the trapezium cluster @xcite , comprises the stars located within 0.3 pc ( @xmath0 2 arcmin ) of @xmath1c orionis , it has an inferred stellar density of about 8000 stars pc@xmath2 and it is one of the densest known region of star formation @xcite . most of the onc members are visible , primarily because the massive stars in the trapezium cluster have swept the gas from the molecular cloud creating a cavity facing towards us . the structure , dynamics and stellar content of the onc have been extensively studied @xcite . the stars in the onc are less than 1 myr old and their masses range from @xmath30.05 m to @xmath050 m @xcite . studies of the outer regions of the orion nebula ( flanking fields ) have revealed the presence of young stars of ages between 1 and 3 myrs old @xcite , with an accretion disk fraction of about 40% @xcite . the orion nebula provides an excellent laboratory for studying pre - main sequence ( pms ) stars , given its proximity ( 470 pc ) , its age and its stellar diversity . pms stars are strong x - ray emitters ; typical pms stars have x - ray luminosities @xmath4 to @xmath5 above those observed in older main sequence stars @xcite . the x - ray emission in low mass stars comes from magnetic reconnection . in the dynamo model , the strength of the magnetic field , and hence the x - ray activity , depends on the rate of differential rotation and on the depth of the outer convective envelope @xcite . there is a clear relationship between rotation rate ( period ) and x - ray luminosity ( @xmath6 ) found in late - type stars in clusters as old as ngc 2547 ( 15 - 40 myrs , * ? ? ? * ) through the hyades ( @xmath0500 myrs , * ? ? ? the ratio between the x - ray and bolometric luminosity , @xmath6/@xmath7 , increases with increasing rotation rate , until the most rapidly rotating stars reach a maximum x - ray luminosity ( or saturation level ) such that @xmath6/@xmath7@xmath8 ( see * ? ? ? * and references within ) . it is much less clear that rotation and @xmath6/@xmath7 are related in younger clusters . @xcite studied a 4.5 square degree region centered in the orion nebula , using x - ray data from the einstein observatory . they found that at least 100 sources were associated with late - type pms stars , and their x - ray activity was not correlated with published rotational periods and spectroscopic rotational velocities . @xcite used rosat x - ray data in a similar study in the orion nebula , finding no dependence of x - ray activity on rotation . more recently , the chandra observatory has provided significantly improved spatial resolution and sensitivity for x - ray observations . @xcite reported x - ray observations of the onc using the chandra observatory acis - i detector . they found more than a thousand x - ray sources , 91% of them associated with known stellar members of the cluster . @xcite also see no obvious correlation between rotation and @xmath6/@xmath7 for their onc sample , and conclude that the x - ray generation mechanism for young pms stars must be different from that responsible in young main sequence stars . @xcite analyzed data for a number of young associations and clusters ( including orion ) , and agree that there is little correlation between @xmath6/@xmath7 and rotation at very young ages , but conclude that the data are consistent with a single physical mechanism , where the orion - age stars are simply all at or near the saturation level . we intend to use our orion flanking field data and other new chandra data for ngc 2264 @xcite to help determine at what age the relationship between rotation and @xmath6/@xmath7 emerges . in the present paper , we present results of chandra observations of two of the flanking fields ( ff ) in the orion nebula ( fields # 2 & # 4 from * ? ? ? * ) , just outside the onc . we discuss source detection , variability and @xmath6 determination , providing a catalog of 417 x - ray sources . we present evidence that the x - ray selected sample of pms stars in the flanking fields in orion are older than a similarly selected sample in the onc . in paper iii @xcite , we will discuss in more detail the relationships found here between rotation rate , mass accretion rate , disk indicators , and x - ray luminosity , in our field of ngc 2264 and the two orion flanking fields .

we present results of chandra observations of two flanking fields ( ff ) in orion , outside the orion nebula cluster ( onc ) . the optical and infrared photometry for the stars identified as x - ray sources are consistent with most of these objects being pre - main sequence stars with ages younger than 10 myr .

we present results of chandra observations of two flanking fields ( ff ) in orion , outside the orion nebula cluster ( onc ) . the observations were taken with the acis - i camera with an exposure time of about 48 ks each field . we present a catalog of 417 sources , which includes x - ray luminosity , optical and infrared photometry and x - ray variability information . we have found 91 variable sources , 33 of which have a flare - like light curve , and 11 of which have a pattern of a steady increase or decrease over a 10 hour period . the optical and infrared photometry for the stars identified as x - ray sources are consistent with most of these objects being pre - main sequence stars with ages younger than 10 myr . we present evidence for an age difference among the x - ray selected samples of ngc 2264 , orion ff , and onc , with ngc 2264 being the oldest , and onc being the youngest .

astro-ph0405003

c

we present a catalog of orion x - ray sources from two flanking fields . the observations were taken with the acis - i on board the chandra x - ray observatory . the catalog , consisting of 417 sources , includes x - ray luminosity , optical and infrared photometry and x - ray variability information . we found 91 variable sources , 33 of which have a flare like light curve , and 11 of which have a pattern of a steady increase or decrease . from the optical and infrared counterparts of the x - ray sources , we have learned that most of the x - ray sources have colors consistent with ctts that are younger than @xmath58 years . we argue that the data are consistent with an age difference among the x - ray selected samples of ngc 2264 , orion ff , and onc , with ngc 2264 being the oldest , and onc being the youngest . this catalog of x - ray sources will be used to study the relationship between rotational properties and x - ray characteristics of orion and ngc 2264 stars in paper iii @xcite . we plan to discuss correlations of @xmath6/@xmath7 with rotation rate ( period and @xmath69sin@xmath70 ) , disk indicators ( @xmath71 , @xmath52 , @xmath72 , and @xmath73 ) , and mass accretion rate as derived from @xmath72 excess . we will also compare the @xmath6/@xmath7 values found here with those from other young clusters . we thank the anonymous referee for her / his careful review of the manuscript . financial support for this work was provided by nasa grant go2 - 3011x . this research has made extensive use of nasa s astrophysics data system abstract service , the simbad database , operated at cds , strasbourg , france , and the nasa / ipac infrared science archive , which is operated by the jet propulsion laboratory , california institute of technology , under contract with the national aeronautics and space administration . the research described in this paper was partially carried out at the jet propulsion laboratory , california institute of technology , under a contract with the national aeronautics and space administration . brandt , w. n. , alexander , d. m. , hornschemeier , a. e. , garmire , g. p. , schneider , d. p. , barger , a. j. , bauer , f. e. , broos , p. s. , cowie , l. l. , townsley , l. k. , burrows , d. n. , chartas , g. , feigelson , e. d. , griffiths , r. e. , nousek , j. a. , & sargent , w. l. w. , 2001 , , 122 , 2810 reid , i. n. , brewer , c. , brucato , r. j. , mckinley , w. r. , maury , a. , mendenhall , d. , mould , j. r. , mueller , j. , neugebauer , g. , phinney , j. , sargent , w. l. w. , schombert , j. , & thicksten , r. , 1991 , , 661 rosati , p. , tozzi , p. , giacconi , r. , gilli , r. , hasinger , g. , kewley , l. , mainieri , v. , nonino , m. , norman , c. , szokoly , g. , wang , j. x. , zirm , a. , bergeron , j. , borgani , s. , gilmozzi , r. , grogin , n. , koekemoer , a. , schreier , e. , zheng , w. , 2002 , , 566 , 667 rcllcccccccrc + n001 & cxorrs j053442.6 - 044215 & 5 34 42.70 & -4 42 15.294 & 10.93 & 17.50 & 1.00 & 35.9 & 17.25 & 0.114e-12 & 30.48 & 93 & + n002 & cxorrs j053444.5 - 044214 & 5 34 44.53 & -4 42 14.807 & 10.55 & 16.30 & 1.00 & 36.4 & 12.88 & 0.848e-13 & 30.35 & 0 & v , s + n004 & cxorrs j053448.2 - 044740 & 5 34 48.24 & -4 47 40.865 & 7.77 & 9.50 & 0.98 & 40.9 & 36.05 & 0.237e-12 & 30.80 & 0 & v , s + n005 & cxorrs j053448.5 - 044956 & 5 34 48.60 & -4 49 56.658 & 7.78 & 8.70 & 0.96 & 24.7 & 1.56 & 0.103e-13 & 29.43 & 99 & + n007 & cxorrs j053451.0 - 044341 & 5 34 51.05 & -4 43 41.614 & 8.39 & 10.10 & 0.98 & 38.7 & 10.48 & 0.690e-13 & 30.26 & 0 & v , f + n008 & cxorrs j053451.2 - 044757 & 5 34 51.28 & -4 47 57.405 & 7.00 & 9.40 & 0.99 & 41.6 & 55.40 & 0.365e-12 & 30.98 & 23 & v + n010 & cxorrs j053452.4 - 044941 & 5 34 52.46 & -4 49 41.023 & 6.85 & 6.70 & 0.97 & 36.5 & 1.04 & 0.684e-14 & 29.26 & 100 & + n011 & cxorrs j053453.0 - 044811 & 5 34 53.02 & -4 48 11.677 & 6.55 & 6.20 & 0.96 & 40.5 & 0.44 & 0.290e-14 & 28.88 & 100 & + n012 & cxorrs j053453.8 - 044340 & 5 34 53.82 & -4 43 40.195 & 7.83 & 8.80 & 0.98 & 36.7 & 0.44 & 0.290e-14 & 28.88 & 100 & + n015 & cxorrs j053454.3 - 045413 & 5 34 54.31 & -4 54 13.447 & 8.63 & 10.70 & 0.97 & 40.2 & 2.10 & 0.138e-13 & 29.56 & 97 & + n016 & cxorrs j053454.4 - 044540 & 5 34 54.44 & -4 45 40.342 & 6.73 & 6.50 & 0.97 & 41.8 & 0.26 & 0.171e-14 & 28.66 & 100 & + n017 & cxorrs j053454.5 - 045604 & 5 34 54.58 & -4 56 4.736 & 9.96 & 14.40 & 0.98 & 32.5 & 3.88 & 0.255e-13 & 29.83 & 99 & + n018 & cxorrs j053455.1 - 044827 & 5 34 55.12 & -4 48 27.968 & 6.05 & 5.30 & 0.96 & 40.6 & 24.67 & 0.162e-12 & 30.63 & 2 & v + n019 & cxorrs j053455.6 - 045611 & 5 34 55.67 & -4 56 11.579 & 9.89 & 14.20 & 0.98 & 39.3 & 3.78 & 0.249e-13 & 29.82 & 99 & + n020 & cxorrs j053456.3 - 044548 & 5 34 56.31 & -4 45 48.316 & 6.25 & 5.70 & 0.97 & 37.7 & 1.14 & 0.750e-14 & 29.30 & 100 & x + n021 & cxorrs j053456.3 - 044437 & 5 34 56.39 & -4 44 37.961 & 6.77 & 6.60 & 0.97 & 41.5 & 1.79 & 0.118e-13 & 29.49 & 100 & x + n022 & cxorrs j053456.8 - 044605 & 5 34 56.81 & -4 46 5.044 & 6.01 & 5.30 & 0.97 & 39.8 & 8.12 & 0.534e-13 & 30.15 & 95 & + n025 & cxorrs j053457.9 - 044913 & 5 34 57.90 & -4 49 13.139 & 5.43 & 4.40 & 0.95 & 19.6 & 14.61 & 0.961e-13 & 30.40 & 90 & + n026 & cxorrs j053458.2 - 045052 & 5 34 58.22 & -4 50 52.031 & 5.86 & 5.00 & 0.96 & 40.1 & 0.27 & 0.178e-14 & 28.67 & 100 & + n027 & cxorrs j053459.3 - 045011 & 5 34 59.35 & -4 50 11.837 & 5.36 & 4.30 & 0.95 & 42.7 & 2.40 & 0.158e-13 & 29.62 & 89 & + n029 & cxorrs j053459.6 - 044756 & 5 34 59.63 & -4 47 56.143 & 4.92 & 3.70 & 0.95 & 43.4 & 0.68 & 0.447e-14 & 29.07 & 100 & x + n030 & cxorrs j053459.7 - 045158 & 5 34 59.70 & -4 51 58.602 & 6.18 & 5.50 & 0.96 & 42.0 & 0.62 & 0.408e-14 & 29.03 & 98 & + n031 & cxorrs j053459.8 - 045526 & 5 34 59.87 & -4 55 26.028 & 8.66 & 10.80 & 0.98 & 40.3 & 1.18 & 0.776e-14 & 29.31 & 100 & + n034 & cxorrs j053500.7 - 044649 & 5 35 0.80 & -4 46 49.233 & 4.85 & 3.60 & 0.95 & 34.8 & 1.12 & 0.737e-14 & 29.29 & 99 & + n035 & cxorrs j053500.9 - 044819 & 5 35 0.92 & -4 48 19.319 & 4.60 & 3.30 & 0.95 & 43.7 & 0.93 & 0.612e-14 & 29.21 & 98 & + n037 & cxorrs j053501.9 - 044115 & 5 35 1.96 & -4 41 15.366 & 8.22 & 9.70 & 0.98 & 40.8 & 4.65 & 0.306e-13 & 29.91 & 13 & v + n038 & cxorrs j053502.0 - 044731 & 5 35 2.09 & -4 47 31.843 & 4.36 & 3.00 & 0.95 & 34.9 & 1.14 & 0.750e-14 & 29.30 & 100 & + n039 & cxorrs j053502.3 - 044755 & 5 35 2.33 & -4 47 55.508 & 4.21 & 2.90 & 0.95 & 32.3 & 2.64 & 0.174e-13 & 29.66 & 98 & x + cccccc + n093 & par 1817 & 209.4 & 0.77 & 3.40 & 14.20 + n256 & par 2257 & 65.6 & 0.70 & 2.87 & 4.03 + n218 & par 2140 & 60.6 & 0.56 & 1.96 & 3.61 + n087 & par 1798 & 56.0 & 1.05 & 3.62 & 3.78 + n008 & par 1621 & 55.4 & 0.40 & 2.63 & 3.60 + n097 & par 1834 & 52.5 & 0.00 & 3.58 & 3.35 + n126 & par 1950 & 43.5 & 0.65 & 2.22 & 2.65 + n044 & par 1701 & 35.4 & 0.00 & 2.74 & 2.54 + n004 & par 1598 & 36.0 & 0.00 & 2.11 & 2.21 + n137 & par 1967 & 30.3 & 0.31 & 1.39 & 1.88 + n165 & par 2043 & 41.4 & 0.30 & 1.31 & 2.54 + n124 & par 1935 & 27.8 & 0.00 & 1.23 & 1.65 + n190 & par 2081 & 29.5 & 0.85 & 4.40 & 1.77 + n222 & par 2145 & 27.0 & 0.61 & 2.40 & 1.54 + n018 & par 1651 & 24.7 & 0.84 & 3.88 & 1.60 + n195 & r01 2133 & 21.1 & 0.40 & 3.25 & 1.25 + n080 & par 1778 & 20.3 & 0.00 & 4.02 & 1.16 + n208 & par 2109 & 17.0 & 0.24 & 1.07 & 0.91 + n081 & smmv 1944 & 17.3 & 0.00 & 1.96 & 1.01 + n156 & par 2017 & 67.2 & 0.00 & 1.38 & 4.06 + n046 & par 1710 & 16.4 & 0.89 & 4.36 & 0.95 + n130 & par 1948 & 16.1 & 0.87 & 5.02 & 0.91 + n001 & r01 1413 & 17.2 & 0.00 & 6.76 & 0.82 + n175 & par 2064 & 12.9 & 0.00 & 1.01 & 0.75 + + s249 & par 2069 & 200.9 & 0.85 & 3.71 & 13.30 + s168 & par 1828 & 100.8 & 1.00 & 4.80 & 7.21 + s238 & par 2048 & 103.8 & 0.66 & 3.34 & 7.25 + s020 & par 1553 & 52.0 & 0.70 & 2.43 & 3.40 + s198 & par 1929 & 37.5 & 0.66 & 2.23 & 2.41 + s040 & par 1756 & 34.7 & 0.77 & 2.70 & 2.16 + s183 & par 1874 & 31.6 & 1.00 & 4.45 & 2.13 + s152 & par 1787 & 27.3 & 1.33 & 5.82 & 1.85 + s058 & par 1643 & 26.5 & 0.64 & 2.02 & 1.34 + s172 & par 1846 & 21.2 & 0.64 & 2.65 & 1.26 + s202 & par 1942 & 19.5 & 0.78 & 2.66 & 1.12 + s174 & par 1848 & 19.5 & 0.86 & 3.70 & 1.14 + s022 & par 1564 & 17.8 & 0.64 & 1.63 & 1.12 + s047 & par 1613 & 16.0 & 0.69 & 1.76 & 0.86 + s016 & par 1535 & 15.4 & 0.64 & 1.63 & 0.85 + s039 & par 1616 & 15.6 & 0.64 & 1.47 & 0.85 + s176 & par 1876 & 14.4 & 0.81 & 3.36 & 0.86 + s079 & r01 1603 & 13.1 & 0.32 & 3.58 & 0.64 + s025 & par 1571 & 13.4 & 1.04 & 1.88 & 0.84 + s104 & chs 7005 & 21.2 & 0.00 & 0.00 & 0.96 cllrrrrrrr r01 1413 & 5 34 42.616 & -4 42 14.86 & n001 & & 18.79 & 15.52 & 13.07 & 10.99 & 9.94 + par 1567 & 5 34 44.512 & -4 42 13.71 & n002 & 0.04 & 15.38 & 13.53 & 12.36 & 11.49 & 10.89 + par 1598 & 5 34 48.155 & -4 47 39.98 & n004 & 0.11 & 16.63 & 14.08 & 12.05 & 10.73 & 9.97 + chs 5807 & 5 34 48.548 & -4 49 56.72 & n005 & & & & & 13.97 & 12.07 + par 1620 & 5 34 50.988 & -4 43 41.35 & n007 & & 16.02 & 13.60 & 12.14 & 11.09 & 10.43 + par 1621 & 5 34 51.204 & -4 47 56.91 & n008 & & 15.85 & 13.45 & 11.88 & 10.66 & 9.96 + r01 1536 & 5 34 52.410 & -4 49 40.29 & n010 & & & 19.34 & 16.40 & 13.76 & 12.45 + par 1639 & 5 34 52.963 & -4 48 10.56 & n011 & & & 17.10 & 15.20 & & 12.23 + r01 1563 & 5 34 53.670 & -4 43 40.69 & n012 & & & 18.12 & 15.82 & 14.57 & 13.95 + 2mass j05345431 - 0454129 & 5 34 54.313 & -4 54 13.447 & n015 & & & & & 14.81 & 12.42 + r01 1570 & 5 34 54.391 & -4 45 39.22 & n016 & & & 19.70 & 16.11 & 13.83 & 13.11 + r01 1572 & 5 34 54.501 & -4 56 4.96 & n017 & & & 18.05 & 14.65 & 12.11 & 10.93 + par 1651 & 5 34 55.052 & -4 48 27.54 & n018 & 0.47 & 16.27 & 14.12 & 12.44 & 11.13 & 10.41 + r01 1586 & 5 34 55.574 & -4 56 11.23 & n019 & & & 19.11 & 15.25 & 12.47 & 11.00 + chs 6568 & 5 34 56.817 & -4 46 4.78 & n022 & & & & & & 11.46 + r01 1610 & 5 34 57.827 & -4 49 12.54 & n025 & & & 16.99 & 14.43 & 12.73 & 11.91 + r01 1620 & 5 34 58.184 & -4 50 51.45 & n026 & & & 18.61 & 15.72 & 13.30 & 12.38 + par 1672 & 5 34 59.269 & -4 50 11.41 & n027 & & & 15.85 & 13.38 & 11.77 & 10.93 + r01 1635 & 5 34 59.636 & -4 51 57.50 & n030 & & & 21.60 & 16.58 & 13.94 & 12.94 + 2mass j05345988 - 0455272 & 5 34 59.874 & -4 55 26.028 & n031 & & & & & 17.05 & 14.02 + r01 1647 & 5 35 0.740 & -4 46 49.07 & n034 & & & 16.52 & 13.99 & 12.44 & 11.69 + r01 1651 & 5 35 0.846 & -4 48 18.71 & n035 & & & 17.23 & 14.22 & 12.38 & 11.58 + r01 1659 & 5 35 1.890 & -4 41 14.54 & n037 & 1.35 & & 18.86 & 15.55 & 13.22 & 12.14 + r01 1660 & 5 35 2.000 & -4 47 30.73 & n038 & & & 21.16 & 15.93 & 13.49 & 12.86 + par 1692 & 5 35 2.303 & -4 49 15.92 & n040 & 0.24 & & 16.74 & 14.28 & 12.70 & 11.88 + r01 1663 & 5 35 2.574 & -4 49 29.12 & n042 & & 17.68 & 14.87 & 12.60 & 11.09 & 10.22 + par 1700 & 5 35 2.891 & -4 48 32.54 & n043 & & 16.57 & 16.52 & 14.61 & 13.21 & 12.51 + par 1701 & 5 35 3.229 & -4 49 20.29 & n044 & & 14.31 & 13.01 & 11.32 & 9.96 & 9.08 + r01 1677 & 5 35 3.252 & -4 56 42.63 & n045 & & 18.24 & 15.60 & 13.58 & 12.33 & 11.57 + par 1710 & 5 35 3.622 & -4 50 52.77 & n046 & & 16.47 & 15.11 & 13.19 & 11.47 & 10.36 + 2mass j05350376 - 0447516 & 5 35 3.748 & -4 47 51.576 & n047 & & & & & 14.24 & 13.47 + par 1709 & 5 35 4.292 & -4 46 42.20 & n048 & & & & & 9.79 & 9.26 + 2mass j05350469 - 0452418 & 5 35 4.668 & -4 52 41.560 & n049 & & & & & 14.35 & 12.67 + rlllll n001 & & r01 1413 & chs 5282 & 2mass j05344268 - 0442148 & smmv 1089 + n002 & par 1567 & r01 1429 & chs 5438 & 2mass j05344454 - 0442146 & tian 125,rosat 42,smmv 1126 + n004 & par 1598 & r01 1483 & & 2mass j05344823 - 0447401 & rosat 52 + n005 & & & chs 5807 & 2mass j05344854 - 0449568 & + n007 & par 1620 & r01 1521 & & 2mass j05345106 - 0443414 & + n008 & par 1621 & r01 1522 & chs 6064 & 2mass j05345128 - 0447570 & einstein 56,rosat 59 + n010 & & r01 1536 & & 2mass j05345249 - 0449404 & + n011 & par 1639 & r01 1542 & & 2mass j05345302 - 0448104 & + n012 & & r01 1563 & & 2mass j05345374 - 0443407 & + n015 & & & & 2mass j05345431 - 0454129 & + n016 & & r01 1570 & & 2mass j05345446 - 0445393 & + n017 & & r01 1572 & & 2mass j05345458 - 0456053 & + n018 & par 1651 & r01 1578 & chs 6412 & 2mass j05345513 - 0448277 & rosat 72 + n019 & & r01 1586 & chs 6469 & 2mass j05345566 - 0456117 & + n022 & & & chs 6568 & 2mass j05345682 - 0446047 & + n025 & & r01 1610 & & 2mass j05345791 - 0449127 & smmv 1452 + n026 & & r01 1620 & & 2mass j05345826 - 0450517 & + n027 & par 1672 & r01 1633 & & 2mass j05345935 - 0450117 & + n030 & & r01 1635 & & 2mass j05345971 - 0451578 & + n031 & & & & 2mass j05345988 - 0455272 & + n034 & & r01 1647 & & 2mass j05350082 - 0446491 & + n035 & & r01 1651 & & 2mass j05350093 - 0448188 & + n037 & & r01 1659 & chs 7084 & 2mass j05350196 - 0441145 & + n038 & & r01 1660 & & 2mass j05350208 - 0447308 & + n040 & par 1692 & r01 1662 & & 2mass j05350238 - 0449161 & + n042 & & r01 1663 & & 2mass j05350265 - 0449293 & + n043 & par 1700 & r01 1668 & chs 7175 & 2mass j05350298 - 0448326 & + n044 & par 1701 & r01 1676 & chs 7211 & 2mass j05350326 - 0449209 & tian 158 + n045 & & r01 1677 & & 2mass j05350333 - 0456430 & + n046 & par 1710 & r01 1678 & chs 7251 & 2mass j05350370 - 0450530 & + n047 & & & & 2mass j05350376 - 0447516 & + n048 & par 1709 & & & 2mass j05350421 - 0446435 & tian 161 + n049 & & & & 2mass j05350469 - 0452418 & + n050 & & & & 2mass j05350481 - 0447089 & + lllllccccc & & chs 10870 & & & @xmath3 6.30 & @xmath3 0.3447 & @xmath30.0227 & @xmath3 28.78 + par 2083 & & & & tian 250 & @xmath310.70 & @xmath3 0.4994 & @xmath30.0329 & @xmath3 28.94 + par 2131 & & & 2mass j05353948 - 0451216 & tian 258 & @xmath3 9.80 & @xmath3 0.2455 & @xmath30.0161 & @xmath3 28.63 + par 1654 & r01 1599 & & 2mass j05345622 - 0445574 & tian 150 & @xmath3 8.00 & @xmath3 0.2016 & @xmath30.0133 & @xmath3 28.54 + par 1708 & & & 2mass j05350478 - 0443546 & tian 162 & @xmath3 8.40 & @xmath3 0.2328 & @xmath30.0153 & @xmath3 28.61 + & & chs 8034 & 2mass j05351065 - 0442075 & & @xmath3 6.30 & @xmath3 0.1464 & @xmath30.0096 & @xmath3 28.41 + & & chs 8467 & 2mass j05351406 - 0453112 & & @xmath3 5.10 & @xmath3 0.1671 & @xmath30.0110 & @xmath3 28.46 + & r01 1937 & chs 9321 & 2mass j05351974 - 0448180 & & @xmath3 3.00 & @xmath3 0.1881 & @xmath30.0124 & @xmath3 28.51 + & r01 1720 & & 2mass j05350693 - 0449097 & & @xmath313.90 & @xmath3 0.8425 & @xmath30.0554 & @xmath3 29.17 + & r01 1806 & & 2mass j05351282 - 0539077 & jw 398 & @xmath3 3.00 & @xmath3 0.2237 & @xmath30.0150 & @xmath3 28.60 + & & chs 9056 & 2mass j05351795 - 0535157 & jw 579,smmv 2470 & @xmath3 6.70 & @xmath3 0.1530 & @xmath30.0103 & @xmath3 28.43 + & & & 2mass j05351898 - 0537234 & hbjm 10548 & @xmath3 3.80 & @xmath3 0.1427 & @xmath30.0096 & @xmath3 28.40 + & & & & jw 618 & @xmath3 5.60 & @xmath3 0.1889 & @xmath30.0127 & @xmath3 28.53 + par 1810 & r01 1795 & & 2mass j05351235 - 0536403 & jw 384 & @xmath310.10 & @xmath3 0.4175 & @xmath30.0280 & @xmath3 28.87 + par 1898 & & & 2mass j05351596 - 0539147 & jw 514,tian 196 & @xmath3 3.00 & @xmath3 0.1990 & @xmath30.0134 & @xmath3 28.55 + & r01 1949 & & 2mass j05352074 - 0537536 & jw 667 & @xmath3 8.50 & @xmath3 0.3344 & @xmath30.0225 & @xmath3 28.77 + & r01 1451 & & 2mass j05344609 - 0537312 & jw 79 & @xmath312.10 & @xmath3 0.3498 & @xmath30.0235 & @xmath3 28.79 + cccccccccc 1.01.5 & 3.81 & 4.21 & 4.44 & 3.18 & 3.71 & 4.22 & 2.66 & 3.43 & 3.90 + 1.52.0 & 4.30 & 4.88 & 5.25 & 4.15 & 4.53 & 4.88 & 3.63 & 4.30 & 4.69 + 2.02.5 & 5.10 & 5.58 & 5.98 & 4.81 & 5.30 & 5.72 & 4.57 & 4.94 & 5.45 +

we present a catalog of 417 sources , which includes x - ray luminosity , optical and infrared photometry and x - ray variability information . we have found 91 variable sources , 33 of which have a flare - like light curve , and 11 of which have a pattern of a steady increase or decrease over a 10 hour period . we present evidence for an age difference among the x - ray selected samples of ngc 2264 , orion ff , and onc , with ngc 2264 being the oldest , and onc being the youngest .

we present results of chandra observations of two flanking fields ( ff ) in orion , outside the orion nebula cluster ( onc ) . the observations were taken with the acis - i camera with an exposure time of about 48 ks each field . we present a catalog of 417 sources , which includes x - ray luminosity , optical and infrared photometry and x - ray variability information . we have found 91 variable sources , 33 of which have a flare - like light curve , and 11 of which have a pattern of a steady increase or decrease over a 10 hour period . the optical and infrared photometry for the stars identified as x - ray sources are consistent with most of these objects being pre - main sequence stars with ages younger than 10 myr . we present evidence for an age difference among the x - ray selected samples of ngc 2264 , orion ff , and onc , with ngc 2264 being the oldest , and onc being the youngest .

astro-ph0405187

c

we have presented the rest - frame optical spectra of a sample of uv - selected star - forming galaxies that are also bright in the rest - frame optical . the [ nii]/@xmath4 line ratios of the majority of these galaxies indicate that they have already been enriched to at least solar oxygen abundance at a lookback time of @xmath67 gyr . it is worthwhile to consider their metallicities and luminosities along with those of local star - forming and elliptical galaxies . over a factor of 100 in ( o / h ) abundance and 11 magnitudes in blue luminosity , nearby star - forming spiral and irregular galaxies exhibit a strong trend of higher metallicity with increasing luminosity @xcite . elliptical galaxies show a similar correlation between metallicity and luminosity , although their metallicities are measured from absorption indices in late - type stars rather than h ii emission line strengths @xcite . this correlation can be explained if less luminous ( and less massive ) galaxies have larger gas fractions , either because they have lower star - formation rates per unit mass than more massive galaxies , or because they are younger . another way of explaining the correlation is through galactic - scale outflows , which could remove a larger fraction of gas and metals from less massive galaxies , which have shallower gravitational potentials , thereby reducing the effective heavy element yield @xcite . both @xcite and @xcite have shown that @xmath147 lyman break galaxies ( lbgs ) are @xmath148 magnitudes overluminous for their metallicities , when compared with the local metallicity - luminosity relation . despite large uncertainties in lbg metallicities , the upper bound of the abundances allowed by the observed lbg @xmath123 values still falls a factor of three in metallicity below the local metallicity luminosity relationship . in figure [ fig : zmb ] we plot the local metallicity@xmath149 relationship ( with data compiled by @xcite ) along with the shaded region allowed for lbgs . in this figure , we also include the luminosity and metallicity measurements for the rest - frame optically luminous @xmath26 star - forming galaxies presented here . for both the lbgs and @xmath2 galaxies , @xmath149 was calculated using best - fit model spectral energy distributions ( see section [ sec : masses ] ) to interpolate the observed broadband @xmath150 colors to rest - frame @xmath151 . while the specific ( o / h ) values and errors implied by the linear @xcite relationship place the @xmath2 galaxies below the metallicity - luminosity relationship for local galaxies , it must also be borne in mind that our estimates of ( o / h ) represent lower limits because of the relative insensitivity of the @xmath125 index when ( o / h ) is higher than solar . furthermore , since ( o / h ) abundances in this plot are derived with the @xmath123 method for the @xmath7 and @xmath152 galaxies and with the @xmath125 method for the @xmath153 @xmath2 galaxies , it is important to acknowledge possible systematic differences between the two methods . as mentioned above , these systematic differences are definitely relevant in the super - solar metallicity regime where [ nii]/@xmath4 is no longer sensitive to increasing ( o / h ) abundance . the oxygen abundance derived from [ nii]/@xmath4 may also be @xmath154 dex lower than the abundance derived from @xmath123 at lower metallicities , where [ nii]/@xmath4 _ is _ sensitive to metallicity @xcite . to estimate ( o / h ) from the @xmath2 [ nii]@xmath4 ratios in a manner more consistent with the @xmath123 abundance determinations for local h ii regions , we examined the emission line data for a set of h ii regions located in eight galaxies in the @xcite sample . uniformly measured @xmath125 and @xmath123 values for these h ii regions are contained in @xcite . the @xmath2 galaxies in our sample have [ nii]/@xmath4 ratios that span from @xmath155 to @xmath156 . h ii regions in the @xcite sample with [ nii]/@xmath4 in this range are found to have @xmath157 , using the upper - branch @xmath123 calibration of @xcite , which corresponds to @xmath158 . while the @xmath123 calibration is in itself untested at these very high values of metallicity and may well suffer from its own systematic uncertainties , it seems very likely that the @xmath159 star - forming galaxies we have observed in this work are enriched to levels comparable to those of the most metal - rich and massive spiral and elliptical galaxies in the local universe . whether solar or super - solar , the metallicities of these galaxies are likely to grow further from @xmath159 to the present time , since we observe them while they are still in the process of actively forming stars at rates of @xmath160 . in one possible scenario , proposed by @xcite to explain the range of ( o / h ) and @xmath149 measurements of star - forming galaxies at @xmath7 , @xmath161 , and @xmath162 , the rest - frame optically bright @xmath2 galaxies in our sample will evolve both in metallicity and luminosity by @xmath162 ; their oxygen abundances will increase by a factor of two , and their luminosities will fade by @xmath163 magnitudes unfortunately , at this point , we can not precisely determine the amount of future star - formation and enrichment in these galaxies ( and therefore tracks in metallicity - luminosity space as a function of redshift ) since we have no information about their molecular gas content or future episodes of gas accretion and infall . in any case , it is important to obtain deeper [ nii ] and @xmath4 measurements of @xmath164 star - forming @xmath2 galaxies in order to determine the @xmath2 metallicity - luminosity relationship over a larger range of rest - frame optical luminosities and relate star - forming @xmath2 galaxies to those at lower redshift . as a first step , we compare galaxies in the current sample with those presented in @xcite , in terms of their rest - frame optical luminosities ( corrected for @xmath4 emission ) and [ nii]/@xmath4 ratios . the current sample of @xmath3 galaxies is characterized by @xmath165 and @xmath69}/{\,{\rm h\alpha}}\rangle=0.27 $ ] , corresponding to @xmath166 . of the 17 galaxies with @xmath4 emission - line flux measurements in @xcite , 14 also have measured @xmath5 magnitudes , from which rest - frame optical luminosities can be calculated . the @xcite galaxies with @xmath5 measurements are fainter on average than the @xmath153 sample , with @xmath167 . it was not possible to estimate [ nii]/@xmath4 on an individual basis for most of the @xcite galaxies , since [ nii ] is not significantly detected in the majority of the spectra . to determine the average [ nii]/@xmath4 , we constructed a composite nirspec spectrum from the 14 galaxies with @xmath5 measurements . in this spectrum , we found [ nii]/@xmath4=0.10 , corresponding to @xmath168 . therefore , the galaxies from @xcite are @xmath169 mag fainter in the rest - frame optical and @xmath170 dex lower in @xmath171 than the current sample . this trend marks the preliminary establishment of a metallicity luminosity relationship at @xmath2 . lrrcccccc q1623-bx274 & 2.4100 & 4.3 & 34 & 28 & 75 & 0.12 & 1.3 & 1.9 + q1623-md66 & 2.1075 & 6.5 & 51 & 10 & 65 & 0.23 & 0.9 & 0.9 + q1623-bx344 & 2.4224 & 7.9 & 62 & 8 & 49 & 0.20 & 1.6 & 1.9 + q1623-bx453 & 2.1816 & 4.9 & 39 & 16 & 174 & 0.27 & 0.4 & 0.9 + q1623-bx528 & 2.2682 & 3.0 & 24 & 18 & 44 & 0.11 & 1.7 & 1.9 + q1623-bx599 & 2.3304 & 7.6 & 60 & 22 & 49 & 0.10 & 1.3 & 1.3 + q1623-bx663 & 2.4333 & 7.8 & 62 & 12 & 33 & 0.13 & 2.0 & 2.3 + the high h ii region metallicities of the @xmath5-bright star - forming @xmath2 galaxies suggest mature systems that have processed a significant fraction of their baryonic material into stars . modeling the broad - band optical and near - infrared @xmath172 spectral energy distributions of these galaxies with population synthesis codes provides an independent test of this hypothesis . following a similar procedure to that of @xcite , we use @xcite models with solar - metallicity and a salpeter initial mass function ( imf ) to deduce stellar masses and ages . dust extinction is taken into account with a @xcite starburst attenuation law . star - forming galaxies . ] in order to determine how well the stellar masses and ages can be constrained , we investigated a range of star - formation histories of the form @xmath173 , with e - folding times of @xmath174 gyr , as well as continuous star - formation models . before modeling the colors , we corrected the @xmath5 magnitudes for the effects of @xmath4 and [ nii ] nebular emission . five of the seven galaxies show evidence of having sustained active star formation over long timescales , are not well described by steeply declining star - formation histories , and appear to have formed at least @xmath175 of stars . only @xmath176 myr models provide acceptable fits to their seds , yielding ages that are significant fractions of the hubble time at @xmath2 . in fact , while constant - star - formation models provide statistically excellent fits to the photometry for these five galaxies , the associated best - fit ages are older than the ages of the universe at each galaxy s redshift . to avoid this contradiction , we only consider models which yield best - fit ages causally allowed by the finite age of the universe . the @xmath177 myr models yield stellar masses of @xmath178 and ages of @xmath179 gyr , whereas the maximally - allowed @xmath180 models for each object yield masses of @xmath181 and ages of @xmath182 gyr . both ground - based @xmath183 and @xmath140-band , and _ spitzer _ rest - frame near - infrared photometry will help to discriminate between @xmath177 and @xmath184 gyr models . the colors of the remaining two galaxies , bx453 and md66 , provide very little restriction on star - formation history . both of these galaxies can be fit by steeply - declining or constant star - formation models . the best - fit masses for bx453 range from @xmath185 with associated ages ranging from @xmath186 gyr , whereas the masses for md66 range from @xmath187 and ages from @xmath188 gyr . while less massive than the majority of the sample , bx453 and md66 have already formed a significant fraction of the stellar mass of an @xmath189 galaxy in the local universe @xcite . for all seven galaxies , the uncertainties in star - formation history lead to systematic uncertainties in the stellar mass of a factor of @xmath163 . furthermore , if there is an underlying maximally - old population , hidden at rest - frame uv - to - optical wavelengths by the current episode of star formation , the stellar masses derived here could underestimate the total stellar mass by up to a factor of five @xcite . both the inferred dust extinction , @xmath190 , and dust - corrected star - formation rate depend systematically on the assumed star - formation histories ; specifically , the best - fit models are characterized by more dust - extinction and higher bolometric star - formation rates when we assume larger @xmath180 values . assuming the maximally - allowed @xmath180 for each galaxy yields @xmath191 for the sample , and @xmath192 . in table [ tab : sfr ] , we list the best - fit stellar - population parameters , assuming @xmath193 gyr , which provides causally allowed ages for all galaxies in the sample . figure [ fig : models ] shows plots of the best - fit @xmath193 gyr models . while these objects were selected to be at @xmath2 because they display the colors of star - forming galaxies , it is clear that they are not only metal - rich , but also have large stellar masses . the @xmath2 star - forming galaxies in the sample of @xcite were selected to have intrinsic rest - frame uv colors very similar to those of star - forming lbgs at @xmath7 . in relating the two samples of galaxies , it is important to consider if plausible progenitors of the massive , metal - rich @xmath3 `` bx '' galaxies can be found among the sample of @xmath7 lbgs with near - ir photometry , whose stellar populations were modeled by @xcite . to address this question , we re - model the @xcite sample , using the most current release of the bruzual & charlot population synthesis codes @xcite . for a consistent comparison with the best - fit values presented in table [ tab : sfr ] we assume exponentially declining star - formation histories , with @xmath193 gyr . evolving all the @xmath7 best - fit models forward in time , we compute the star - formation rates and stellar masses formed by @xmath194 . assuming that @xmath190 does not change between @xmath7 and @xmath194 , we also compute the predicted @xmath37 and @xmath5 magnitudes , and @xmath195 , @xmath32 colors . the predicted uv colors can be used to determine if a galaxy would be recovered by the @xmath2 uv criteria of @xcite , and the predicted near - ir magnitudes indicate whether or not a galaxy would be included in the rest - frame optically bright sample presented here , with @xmath3 . at least 15% of the @xmath7 lbgs fit by @xcite have stellar population models time - evolved to @xmath194 with stellar masses , star - formation rates , @xmath190 and age within the range of properties of the @xmath3 bx galaxies presented here . the time - evolved @xmath1 colors of these lbgs satisfy the uv criteria of @xcite , and they also have @xmath153 . therefore , at least 15% of the @xmath196 lbgs modeled by @xcite constitute plausible progenitors for the @xmath5-bright bx objects . as shown below , the @xmath5-bright bx s have a comoving number density that s only 14% as high as that of lbgs in the @xcite sample , so we conclude that most of them could have been lbgs in the past . it is now possible to estimate the stellar mass density associated with @xmath197 uv - selected @xmath2 objects . first we estimate the average mass of the 7 objects with [ nii]/@xmath4 measurements . taking into account the systematic uncertainties due to the range of allowed star - formation histories , we find @xmath198 . this average mass should be representative of the entire sample of @xmath3 @xmath2 galaxies since the distributions of @xmath32 and @xmath39 colors of the seven galaxies with mass estimates are similar to those of the entire sample of rest - frame optically luminous objects . rcc @xmath199 & 0/48 & 39 + @xmath200 & 6/51 & 13 + @xmath201 & 145/301 & 7 + @xmath202 & 386/556 & 8 + next we estimate the comoving space density of @xmath3 @xmath2 uv - selected galaxies . in the q1623 wirc pointing , which covers @xmath203 , there are 87 `` bx '' objects with @xmath153 , including 13 galaxies with confirmed redshifts between @xmath204 , one broad - lined qso at @xmath205 , four stars , and two low - redshift galaxies at @xmath206 . the remaining 67 photometric @xmath2 candidates have either not been attempted spectroscopically or have been attempted unsuccessfully , with undetermined redshifts . to estimate the number of @xmath153 galaxies without spectroscopic redshifts that are likely to fall in the redshift range of interest , we use the redshift statistics as a function of @xmath37 magnitude from our total sample of 956 bx objects with spectroscopic information @xcite . based on the bx high - redshift fractions and the distribution of @xmath37 magnitudes for the 67 @xmath3 sources without redshifts presented in table [ tab : rzbx ] ( i.e. multiplying the second column of table [ tab : rzbx ] by the third column ) , we estimate that an additional 11 @xmath3 galaxies without measured redshifts are likely to be at @xmath204 . the total number of @xmath3 bxs at @xmath204 is therefore @xmath207 . weighted by the bx redshift selection function @xcite , the comoving volume between @xmath204 is @xmath208 . over the entire q1623 wirc pointing , the space - density of @xmath204 uv - selected objects with @xmath3 is therefore @xmath209 . the space density of massive galaxies is of course prone to large sample variance because such objects are expected to be strongly clustered . while not yet properly quantified , initial statistics from our two other fields with @xmath5-band data suggest variations of a factor of @xmath163 from field to field . multiplying this space density by the average mass of the rest - frame optically luminous objects we obtain @xmath210 , which is 4% of the @xmath152 stellar mass density determined by @xcite . the @xmath153 objects represent only @xmath67% of the sample of bx objects at @xmath2 , and since we expect to find massive systems down to significantly fainter @xmath5 magnitudes , this figure represents an extreme lower limit on the stellar mass density associated with uv - selected star - forming galaxies at @xmath2 . in the future , when we have the distribution of stellar masses over a much wider range in luminosity in hand , we will determine a more robust constraint on the stellar mass density at @xmath159 , extending the work of @xcite to a larger cosmic volume . there are other current surveys targeting massive galaxies in the same redshift range . it is instructive to compare the properties of the @xmath3 uv - selected objects presented here with those of the galaxies in the k20 survey @xcite and the gemini deep deep survey ( gdds ; * ? ? ? the k20 project is a spectroscopic survey of @xmath211 @xmath3 objects , 9 of which have been spectroscopically confirmed in the redshift range @xmath212 . @xcite demonstrate that this subsample of galaxies is characterized by dust - corrected star - formation rates of @xmath213 , constant star - formation ages of @xmath214 gyr , and stellar masses of @xmath215 . six of the galaxies in @xcite are at @xmath216 , and four of them have optical colors that satisfy the `` bx '' criteria presented in @xcite . these four galaxies have @xmath217 and constant star - formation ages of @xmath218 gyr , very similar to the properties of bx453 and md66 when constant star - formation histories are assumed . of the three galaxies in @xcite that are at @xmath219 , two would be recovered by the `` bm '' criteria of @xcite , which target star - forming @xmath220 galaxies . since the k20 survey uses a different optical filter set from that of the @xcite survey , we calculated the @xmath1 colors of the @xcite galaxies by passing the best - fit redshifted , dust - reddened , constant star - formation models ( from their table 1 ) through the @xmath1 filter set . there appears to be significant overlap between the @xmath3 uv - selected objects and the high - redshift tail of the k20 survey . furthermore , the space density of @xmath221 k20 objects is @xmath222 , which is very comparable to the space density of @xmath3 uv - selected objects at @xmath204 in the q1623 field , @xmath223 . finally , the distribution of stellar masses of the k20 and rest - frame optically luminous uv - selected objects are very similar ( with the exception of one k20 object that has @xmath224 and would not be selected as a bx ) . the additional uv - selection criteria appear to recover the majority of k20 objects , because most @xmath225 galaxies harbor active star formation at @xmath2 . while the majority of the 300 galaxies in the gdds survey are at @xmath226 , this infrared - selected @xmath227 survey contains a small high - redshift tail of @xmath228 galaxies @xcite . using gdds galaxies to trace the evolution of stellar mass - density in the universe , @xcite find a @xmath229 mass density for @xmath230 objects of @xmath231 . below @xmath232 , the @xmath233 gdds becomes incomplete for objects with the highest mass - to - light ratios . the gdds masses and mass densities were calculated assuming an imf that turns over below @xmath234 @xcite ; it is therefore necessary to multiply the gdds numbers by a factor of 1.82 for a meaningful comparison with the results presented here , derived using a salpeter imf . the range of masses of the spectroscopically confirmed gdds @xmath229 galaxies is very similar to that of the @xmath3 uv - selected objects , while the mass density , computed down to a limiting magnitude of @xmath227 is @xmath63 times higher . a more fair comparison in mass densities will result when we have determined the stellar masses of fainter uv - selected objects . nonetheless , it is still currently possible to determine how complementary the uv - selected and gdds surveys are in the @xmath235 redshift range , since one of the gdds survey areas , the ssa22 field , has also been imaged in the @xmath1 filter set as part of the @xmath7 lbg survey @xcite . in the ssa22a field , there are three spectroscopically confirmed gdds galaxies with @xmath229 , and four with uncertain redshifts of @xmath236 @xcite . all three of the @xmath229 galaxies are recovered with the bx / bm @xmath1-selection criteria , and three of the four putative @xmath216 objects would be selected as bxs . at @xmath237 , there are 12 gdds objects in the ssa22a field , half of which would be recovered by the bx / bm uv - selection criteria . the 50% overlap between gdds galaxies at @xmath237 and bx / bm objects is not especially meaningful since the bm color criteria are intended to select galaxies at @xmath220 , and the bx color criteria target galaxies at @xmath238i.e . @xmath237 lies at the edge of the bx / bm selection function , where the selection efficiency drops off . however , the large overlap of the gdds and bx / bm surveys at @xmath235 is again consistent with the idea that even @xmath5-band selected surveys that are supposed to be `` mass - selected '' include a significant fraction of star - forming galaxies at @xmath2 . lcccccc q1623-bx274 & 121 & 0.28 & 0.20 & 1.27 ( 0.70 ) & 5.00 & 2.76 ( 1.52 ) + q1623-md66 & 120 & 0.28 & 0.05 & 0.49 ( 0.27 ) & @xmath239 & 1.19 ( 0.65 ) + q1623-bx344 & 92 & 0.16 & 0.20 & 1.06 ( 0.58 ) & 2.00 & 2.18 ( 1.20 ) + q1623-bx453 & 61 & 0.07 & 0.01 & 0.49 ( 0.27 ) & @xmath239 & 0.92 ( 0.51 ) + q1623-bx528 & 142 & 0.58 & 0.20 & 1.09 ( 0.60 ) & 2.00 & 2.47 ( 1.36 ) + q1623-bx599 & 162 & 0.50 & 0.20 & 0.83 ( 0.46 ) & 5.00 & 1.69 ( 0.93 ) + q1623-bx663 & 132 & 0.45 & 0.20 & 1.06 ( 0.58 ) & 1.00 & 2.35 ( 1.29 ) + the preceding discussion relies on population synthesis models of the galaxy colors to infer stellar masses and therefore the comoving stellar mass density in large galaxies at @xmath2 . rest - frame optical spectroscopy allows for a completely independent probe of galaxy mass : the @xmath4 velocity dispersion . a physical scale - length and assumption of the geometric configuration are necessary to convert the velocity dispersion into a dynamical mass . in previous determinations of high - redshift star - forming galaxy dynamical masses @xcite , a spherically - symmetric distribution of matter was assumed , and the physical scale - length adopted was the typical @xmath7 or @xmath2 galaxy continuum half - light radius , as determined from _ hubble space telescope _ images , @xmath2400203 . from the excellent seeing conditions during our nirspec exposures , we also determine @xmath4 half - light radii of 02 - 03 . using these radii , and assuming a spherical geometry , we determine dynamical masses with the formula : @xmath241 . dynamical mass estimates are listed in table [ tab : mcomp ] , as well as stellar masses inferred from the smallest @xmath180 allowed by the galaxy photometry , and the largest @xmath180 allowed by the age of the universe constraint . as discussed in section [ sec : masses ] , the stellar mass of the best - fit model is an increasing function of the assumed time - constant , @xmath180 . the actual stellar mass for each object lies somewhere between the limits listed in table [ tab : mcomp ] ( neglecting the mass of an underlying maximally - old burst ) . for every galaxy , if a salpeter imf extending down to @xmath242 is assumed , the allowed range of stellar mass exceeds the calculated dynamical mass within @xmath243 . for bx663 , md66 , bx528 , and bx599 , this discrepancy is roughly a factor of @xmath148 , whereas for bx344 , bx274 , and bx453 , the stellar mass estimate exceeds the dynamical mass by an order of magnitude . perhaps this discrepancy is not surprising , given that the galaxy stellar mass was determined from luminosities and colors extending over a physical region in some cases several times as large in radius as the region enclosed by the half - light radius . a larger radius may be more suitable for inferring the dynamical mass . indeed , with the assumption of a constant @xmath244 ratio as a function of radius , the mass enclosed within @xmath243 should be multiplied by 2 in order to compare with the total stellar mass . furthermore , there are observational effects that may apply if the geometry is not the simple spherically - symmetric one assumed for the calculation . if the emission is extended along a specific axis , the possible misalignment of the slit with this axis must be taken into account . if the configuration of h ii regions is more disk - like , then inclination effects may also cause us to underestimate the the circular velocity , and therefore , velocity dispersion . @xcite estimate that the combination of these two effects may result in an underestimate of a factor of @xmath245 in circular velocity . of course , the numerical coefficient multiplying @xmath246 depends on the assumed geometry as well , and is unity for a disk geometry ( as opposed to 5 , assumed for the spherical configuration ) . independent of slit misalignment and disk inclination effects , the emission within the @xmath4 half - light radius may not sample the full range of rotational velocities of the underlying disk . using local starburst galaxies with well - determined rotation curves , @xcite have shown that the widths of optical emission - lines originating in the bright central regions of local starburst galaxies only sample the solid - body part of the rotation curve , and therefore do not reflect the full circular velocity attained on the flat part of the rotation curve at larger radii . both @xcite and @xcite have pointed out this limitation in interpreting the rest - frame optical linewidths of @xmath7 and @xmath24 galaxies in terms of masses . finally , stellar masses were determined assuming a salpeter imf extending down to @xmath242 , though we have no observational constraints on the low - mass regime of the imf at high redshift . an imf which turns over below @xmath234 , as assumed by @xcite , would lower the stellar mass estimates by a factor of @xmath163 . we assumed the standard salpeter form in section [ sec : masses ] for the purposes of comparing with earlier studies of the stellar mass content of galaxies at low and high redshift @xcite , though a more realistic form for the low - mass end of the imf would significantly reduce the systematic discrepancy between stellar and dynamical masses ( as shown by the values in parentheses in table [ tab : mcomp ] ) . most of the above systematic effects would have caused us either to underestimate the dynamical mass , or overestimate the stellar mass . there is enough uncertainty in our estimates of the low - mass end of the imf , the appropriate radius at which to evaluate @xmath247 , and the geometrical configuration of h ii regions , that the current discrepancy between stellar and dynamical mass estimates does not represent a crisis . however , the method of @xcite and @xcite , using simple assumptions to compute dynamical masses , clearly does not account for the amount of stellar mass derived from modeling the colors of these galaxies . we must understand the nature of these discrepancies before we can trace the evolution of mass in galaxies as a function of redshift .

drawn from a large spectroscopic survey of galaxies photometrically pre - selected by their colors to lie at , these galaxies were chosen for their bright rest - frame optical luminosities ( ) . most strikingly , the majority of the sample of 7 galaxies exhibit [ nii]/ nebular emission line ratios indicative of at least solar h ii region metallicities , at a lookback time of 10.5 gyr . the broadband colors of the-bright sample indicate that most have been forming stars for more than a gyr at , and have already formed stellar masses in excess of . the descendants of these galaxies in the local universe are most likely metal - rich and massive spiral and elliptical galaxies , while plausible progenitors for them can be found among the population of lyman break galaxies . while the-bright galaxies appear to be highly evolved systems , their large luminosities and uncorrected star - formation rates of indicate that active star formation is still ongoing . the luminous uv - selected objects presented here comprise more than half of the high - redshift ( ) tails of current-band - selected samples such as the k20 and gemini deep deep surveys .

we present results of near - ir spectroscopic measurements of 7 star - forming galaxies at . drawn from a large spectroscopic survey of galaxies photometrically pre - selected by their colors to lie at , these galaxies were chosen for their bright rest - frame optical luminosities ( ) . most strikingly , the majority of the sample of 7 galaxies exhibit [ nii]/ nebular emission line ratios indicative of at least solar h ii region metallicities , at a lookback time of 10.5 gyr . the broadband colors of the-bright sample indicate that most have been forming stars for more than a gyr at , and have already formed stellar masses in excess of . the descendants of these galaxies in the local universe are most likely metal - rich and massive spiral and elliptical galaxies , while plausible progenitors for them can be found among the population of lyman break galaxies . while the-bright galaxies appear to be highly evolved systems , their large luminosities and uncorrected star - formation rates of indicate that active star formation is still ongoing . the luminous uv - selected objects presented here comprise more than half of the high - redshift ( ) tails of current-band - selected samples such as the k20 and gemini deep deep surveys .

1112.2641

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to realize a quantum computer in the circuit model , it is crucial to have precise control over each of the carriers of quantum information . in addition to keeping the quantum state of the computer protected from unavoidable noise induced by the environment , it is necessary to implement suitable quantum gates , usually in the form of one and two qubits gates . the latter is of particular difficulty , especially when optical quantum systems are used because their interaction is either weak or merely induced by measurements . the paradigm of measurement - based quantum computing ( mbqc ) as pioneered by raussendorf and briegel @xcite and substantially generalized by gross and eisert @xcite allows to get rid of the necessity of performing unitary operations to implement a quantum circuit . instead , the actual computation is performed by preparing a multipartite entangled state , the resource , in a first step followed by adaptively chosen local measurements on this resource . the important improvement stems from the fact that the resource is universal , i.e. , it can be prepared independently of the algorithm one wants to perform . this means that the presumably difficult step , the one which involves entangling operations , can be performed off - line . this resource - preparation may also be probabilistic as it is possible to wait with the implementation of the algorithm until the resource is available . what is more , individual addressing in the final read out step is anyway also required in the circuit model , so this step does not add any further difficulty to the scheme . quantum computing based on continuous - variable ( cv ) quantum optical systems differs from the more conventional notion based on their discrete analogues in not making use of single photons as the carriers of quantum information @xcite . instead , it relies to a large extent on gaussian states and their manipulation . the notable advantage is that gaussian states are easier to prepare in the laboratory , the corresponding interactions are often stronger and easier to accomplish , and some measurements , e.g. , homodyne detection , can be performed with an efficiency substantially surpassing the one of single - photon measurements . however , quantum information protocols using gaussian states only , gaussian operations , and gaussian measurements suffer from serious limitations as in this setting neither entanglement distillation @xcite nor error correction against gaussian errors @xcite is possible . also , since one can easily efficiently keep track of first and second moments , any gaussian evolution of gaussian states can be efficiently simulated on a classical computer @xcite , clearly ruling out as the possibility of universal quantum computing . mbqc based on gaussian resource states has been extensively discussed in the literature @xcite due to several features : they are a direct generalization of the well known qubit cluster - state to the continuous - variable regime , they allow for universal quantum computing with gaussian measurements and a single non - gaussian one , and they can be prepared with present day experimental techniques , as already demonstrated . however , if they are not formed out of idealized infinitely squeezed states ( ones that are not contained in hilbert space and would require infinite energy in preparation ) but rather from physical states possessing only finite squeezing , they suffer from exponentially decaying localizable entanglement . this limitation , which applies to any gaussian resource state irrespectively of the permitted class of measurements @xcite , implies that full error correction and the machinery of fault - tolerant quantum computing @xcite , in parts yet to be developed for such continuous - variable systems , appears to be necessary even when both state preparation and measurements are perfect . notably , those restrictions only apply when trying to perform a quantum computation of an _ unbounded _ length . for any _ finite _ length , there exists , for any required accuracy , a physical cluster state such that any quantum operation up to this length is possible with this accuracy . because the widely assumed superior power of quantum computers compared to classical ones manifests itself most prominently in the scaling of the runtime with the problem size , the situation of a quantum computation with unbounded length is in the focus of attention in this work . in addition to schemes based on gaussian cluster states , two more classes of schemes relying on cv - quantum optics have been proposed . the first one is based on superpositions of coherent states which are called schrdinger cat states or , when they have very low amplitude , kitten states @xcite . they can be , in approximation , created by subtracting photons from squeezed states and allow for universal quantum computing by passive operations such as beam - splitters and photon - counting detection only . however , they also suffer from quite severe problems : the probabilistic nature of the quantum operations stemming from the use of non - overlapping basis - elements seems to be the most fundamental one , giving rise to significant overheads . the second approach combines the advantageous features of both discrete and continuous - variable optics @xcite . in these schemes , quantum information is carried by qubits and single qubit operations are performed directly on them . two - qubit operations , in contrast , are performed by letting both qubits interact with a strong cv - mode , the qubus . with this article , we pursue two different , but complementary goals : on the one hand , we aim at clarifying the boundary between settings where cv - mbqc is possible and such situations where this is not the case . for this reason , we will develop a general framework capable of describing quantum computation in the measurement - based paradigm , regardless of the dimension of the carriers of quantum information . within this picture , we can identify some serious limitations giving rise to challenges that have to be overcome . on the other hand , we introduce a first strictly efficient scheme relying only on a simple controlled rotation , which can be realized by an atom - light interaction of the jaynes - cummings type or purely optically by the kerr effect , for the creation of the resource . on the measurement side , we require beamsplitters , phase - space displacers , and photon counting measurements . while this scheme is not fleshed out in all detail of its concrete physical implementation , it should be clear that quantum optical implementations of such ideas are conceivable . the present article is organized as follows : first , we discuss what operations are possible with continuous - variable quantum systems and introduce a framework based on matrix product states ( mps ) to describe mbqc in a general setting . after a discussion of the properties which a cv - mbqc scheme needs to posses in order to be called theoretically efficient , we show the problems of achieving those requirements with gaussian measurements on non - gaussian resource states . last , we provide an example for a feasible scheme and discuss in detail how efficient mbqc can be performed in this situation .

we present strictly efficient schemes for scalable measurement - based quantum computing using continuous - variable systems : these schemes are based on suitable non - gaussian resource states , ones that can be prepared using interactions of light with matter systems or even purely optically . merely gaussian measurements such as optical homodyning as well as photon counting measurements are required , on individual sites . these schemes overcome limitations posed by gaussian cluster states , which are known not to be universal for quantum computations of unbounded length , unless one is willing to scale the degree of squeezing with the total system size . we establish a framework derived from tensor networks and matrix product states with infinite physical dimension and finite auxiliary dimension general enough to provide a framework for such schemes . we also identify some further limitations for any continuous - variable computing scheme from which one can argue that no substantially easier ways of continuous - variable measurement - based computing than the presented one can exist .

we present strictly efficient schemes for scalable measurement - based quantum computing using continuous - variable systems : these schemes are based on suitable non - gaussian resource states , ones that can be prepared using interactions of light with matter systems or even purely optically . merely gaussian measurements such as optical homodyning as well as photon counting measurements are required , on individual sites . these schemes overcome limitations posed by gaussian cluster states , which are known not to be universal for quantum computations of unbounded length , unless one is willing to scale the degree of squeezing with the total system size . we establish a framework derived from tensor networks and matrix product states with infinite physical dimension and finite auxiliary dimension general enough to provide a framework for such schemes . since in the discussed schemes the logical encoding is finite - dimensional , tools of error correction are applicable . we also identify some further limitations for any continuous - variable computing scheme from which one can argue that no substantially easier ways of continuous - variable measurement - based computing than the presented one can exist .

cond-mat0509599

i

the question of coexistence of singlet superconductivity and magnetism has been adressed for many years . it was found that the superconducting order parameter is destroyed by a magnetic field both via the orbital effect @xcite and the paramagnetic effect.@xcite in the usual case of an isotropic three - dimensional ( 3d ) superconductor under an external magnetic field , the orbital effect prevails and leads to the well - known temperature - field phase diagram of conventional type i or ii superconductors.@xcite in contrast , superconductivity is essentially suppressed by the paramagnetic effect in presence of a ferromagnetic exchange interaction . this is also true for quasi - two - dimensional ( 2d ) superconductors under in - plane magnetic field and for heavy fermions materials wherein the orbital effect is partially quenched . in the whole paper , the magnetism is characterized by an internal exchange field @xmath1 ( given in energy units ) which may arise either from an externally applied magnetic field or from ferromagnetic ordering . note that ferromagnetism must be weak in order to avoid complete suppression of superconductivity . this is realized in rare - earth metals or actinides in which the indirect exchange interaction leads to curie temperatures of a few degrees . superconductors with internal homogeneous exchange field @xmath1 exhibit a very special behaviour . according to chandrasekhar@xcite and clogston,@xcite at zero temperature uniform superconductivity should be destroyed when the polarization energy of the free electron gas exceeds the energy gain due to cooper pairing in the bcs ground state . this criterion gives the exchange field @xmath2 where the superconductor should undergo a first - order transition to the normal state , @xmath3 being the zero temperature superconducting gap . larkin and ovchinnikov @xcite and fulde and ferrell @xcite ( fflo ) predicted the existence of a nonuniform superconducting state with higher critical exchange field @xmath4 and second - order transition to the normal state . this prediction was made for 3d superconductors . in quasi-2d superconductors the critical exchange field of the fflo state is even higher , namely @xmath5,@xcite while in quasi - one - dimensional systems there is no paramagnetic limit at all.@xcite the appearance of the modulated fflo state is related to the pairing of electrons with opposite spins which do not have the opposite momenta anymore due to the zeeman splitting . from now on we focus on the 2d case for which a generic temperature - exchange field phase diagram has been established.@xcite at low field and temperature , the ground state is characterized by a uniform superconducting order parameter . a tricritical point , located at @xmath6 and @xmath7 , is the meeting point of three transition lines separating the normal metal , the uniform and the nonuniform superconductors . at @xmath8 , the ( low - field ) uniform superconductor is separated from the ( high - field ) normal metal by a narrow fflo nonuniform superconducting phase . in contrast , at @xmath9 , the system undergoes merely a second - order phase transition from the uniform superconductor to the normal metal when increasing the exchange field . the nonuniform fflo state is settled in a small region of the phase diagram and is very sensitive to impurities,@xcite making it difficult to observe experimentally . nevertheless , several evidences of the fflo state have been obtained recently in organic superconductors @xcite and in heavy fermions compounds , see martin _ _ et al.__@xcite and references therein . in the context of organic and high-@xmath10 superconductors , layered systems made of conducting atomic planes have been extensively studied.@xcite in order to investigate the interplay of superconductivity and magnetism in such anisotropic systems,@xcite andreev _ et al . _ considered a periodic array of alternating ferromagnetic and superconducting 2d planes.@xcite solving the corresponding gorkov equations , these authors established the existence of a @xmath0 state wherein each f layer separates superconducting planes with opposite order parameter . this is relevant for the ruthenocuprate compound rusr@xmath11gdcu@xmath11o@xmath12 which comprises cuo@xmath11 superconducting planes and ruo@xmath11 magnetic planes.@xcite a related system is an isolated f / s / f trilayer which exhibits the so - called superconducting spin - valve effect . namely , its critical temperature is higher in the antiparallel ( ap ) orientation of the layers magnetizations than in the parallel ( p ) orientation both for thick layers@xcite and atomic size layers.@xcite surprisingly , in the atomic thickness limit , the superconducting gap at zero temperature is higher for p orientation of the magnetizations.@xcite hence one expects a transition from ap to p orientation by cooling the system below a finite crossing temperature . the recent progress in molecular beam epitaxy@xcite enables to fabricate such f / s / f trilayer with atomic thicknesses . in this paper , we consider a periodic array of sf bilayers . each bilayer is made of two atomic planes coupled by single electron tunneling . both exchange fields and bcs superconducting pairing are present in each sf plane . the possibility of @xmath13 phase difference between the planes inside each bilayer is also taken into account . in the whole paper , we assume that the coupling @xmath14 between successive bilayers is considerably weaker than the intra - bilayer coupling @xmath15 . our study is performed within the framework of the bcs theory of s - wave superconductivity . solving exactly the gorkov equations in the limit @xmath16 , we first derive the critical temperature and the superconducting gap both for parallel ( p ) and antiparallel ( ap ) orientation of the magnetizations . we show that the critical temperature is higher for the ap orientation than for the p orientation whereas it is the opposite for the zero temperature gap . we also investigate the interlayer josephson current in the small coupling limit : the current increases as a function of the exchange field for ap orientation whereas it is field - independent for the p orientation . furthermore , we find that for low exchange fields and high temperatures , the ground state corresponds to identical superconducting order parameters on adjacent layers . for high enough fields and/or low enough temperatures , the @xmath0 phase ground state is favoured and compete with the fflo state . for the p orientation , the full temperature - exchange field phase diagram is constructed in the two limits of extremely low and high coupling between the planes . as expected , for perturbative coupling between two sf planes , the phase diagram is very close to the quasi-2d superconductor s phase diagram . nevertheless an important change arises . indeed a new @xmath17phase is inserted inside the usual fflo phase close to the tricritical point . for higher tunneling coupling @xmath18 , this @xmath17 phase is pushed to low temperatures @xmath19 and high fields @xmath20 . in this unusual superconducting phase , the zeeman splitting is compensated by the bonding / antibonding energy splitting due to single - electron tunneling between the planes.@xcite as a result , field - induced superconductivity and enhanced paramagnetic limit are realized in this simple model . these new phenomena are encountered due to the introduction of an additional discrete degree of freedom , here the layer index @xmath21 . the layer index acts as a pseudo - spin and thus enlarges the usual spin - space for singlet pairing . this idea was introduced by kulic and hofmann@xcite in the context of two - bands superconductivity for which the pseudo - spin was the band index . nevertheless , these authors did not investigate the presently studied @xmath0 state . the outline of the paper is the following . in sec.ii , we present the model , derive the corresponding gorkov equations and give their exact solutions . in sec.iii , we investigate the critical temperature , the gap and the interlayer josephson current in the small exchange field regime for which there are only uniform superconducting phases . in the last two sections the temperature - exchange field phase diagram of the bilayer is studied thoroughly . in sec.iv , we first construct a ginzburg - landau functional to determine the transitions between the different phases in the low interlayer coupling limit . sec.v is devoted to the opposite limit of strong interlayer coupling . in conclusion , we discuss the conditions for the observation of field - induced superconductivity .

it is demonstrated that such systems exhibit a competition between the nonuniform larkin - ovchinnikov - fulde - ferrel ( fflo ) state and the superconducting state where the sign of the superconducting order parameter is opposite in adjacent layers . we determine the complete temperature - field phase diagram . in the case of low interlayer coupling

we present the detailed theoretical study of a heterostructure comprising of two coupled ferromagnetic superconducting layers . our model may be also applicable to the layered superconductors with alternating interlayer coupling in a parallel magnetic field . it is demonstrated that such systems exhibit a competition between the nonuniform larkin - ovchinnikov - fulde - ferrel ( fflo ) state and the superconducting state where the sign of the superconducting order parameter is opposite in adjacent layers . we determine the complete temperature - field phase diagram . in the case of low interlayer coupling we obtain a new phase inserted within the fflo phase and located close to the usual tricritical point , whereas for strong interlayer coupling the bilayer in the state reveals a very high paramagnetic limit and the phenomenon of field - induced superconductivity .

astro-ph0607514

i

after more than a decade of study , the fundamental parameters of brown dwarfs remain poorly constrained . unlike hydrogen - burning stars , whose effective temperatures and luminosities are approximately age - independent ( at a fixed mass and composition ) on the main sequence , brown dwarfs cool and dim continuously as they age . only one of the fundamental sub - stellar parameters , luminosity , can be estimated independently of the others , through the use of trigonometric parallax and empirically determined bolometric corrections . any attempts to resolve the remaining degeneracies among temperatures , ages , masses , and radii rely on the fortuitous discovery of brown dwarfs in association with stars or clusters of known age . in such cases , brown - dwarf ages can be inferred by demonstrating the physical association of the brown dwarfs , usually as common proper motion secondaries or as members of stellar associations , with stars that have known ages . brown - dwarf masses can be measured from orbital astrometry and radial - velocity monitoring of close ( @xmath7510 au ) binary systems , in which at least one component is sub - stellar . finally , brown - dwarf radii , and hence , effective temperatures and surface gravities , can be measured in sub - stellar eclipsing binaries . the union of these three fortuitous cases , eclipsing brown - dwarf binaries associated with stars , offers the best opportunity for empirical determination of sub - stellar parameters . however , such unusual systems are extremely rare the first one , 2massj 053521840546085 , has only recently been reported @xcite . in all other cases involving brown dwarfs , the estimation of their properties relies to various degrees on the use of theoretical models of sub - stellar evolution ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? consequently , sub - stellar evolution models remain , for the most part , empirically unconfirmed . partial tests have been carried out for systems other than the ideal eclipsing double - line systems . @xcite and @xcite used astrometric measurements of the multiple system ab dor a / b / c to test the mass age luminosity relation at the stellar / sub - stellar boundary . the two analyses offer examples of how sub - stellar evolution models can be tested without considering all degenerate sub - stellar parameters in this case , excluding effective temperature . we note , however , that the conclusions of the two teams differ ( see * ? ? ? * ; * ? ? ? * for further discussion ) , in part because the stellar parameters themselves ( in particular , the stellar ages ) , although used as a reference in either study , may often not be known to the desired or believed level of accuracy . in a separate example , @xcite and @xcite tackle the full set of degenerate sub - stellar parameters using high - resolution spectroscopic observations of brown dwarfs in the upper scorpius and taurus associations . their studies rely on model spectra of brown - dwarf photospheres , constructed independently of sub - stellar evolutionary models , to resolve the mass effective temperature luminosity degeneracy . even though model - dependent , they allow a self - consistent comparison between sub - stellar cooling and photospheric models in the context of empirical data . in the present paper we take a similar approach and discuss the degeneracies among sub - stellar age , luminosity , and effective temperature ( i.e. , excluding mass ) in the context of models of sub - stellar evolution . we address these fundamental properties with the help of a new brown dwarf that we discovered as a common proper motion companion to the 130400 myr - old main - sequence g8 v star hd 203030 ( hip 105232 ; [ sec_observations ] ) . the companion , hd 203030b , has a spectral type of l7.5 , and thus lies very near the transition between l- and t - type sub - stellar photospheres , characterized by the settling of dust and the appearance of methane absorption in the near - ir spectra of brown dwarfs . because dust - settling occurs over a very narrow range of effective temperatures , 15001300 k ( spectral types l6t4 ) , a fact inferred both theoretically @xcite and semi - empirically @xcite , the effective temperature of hd 203030b is expected to be constrained very well . given the known age and luminosity of hd 203030b , we can find its radius and thus offer a constraint on the theory ( [ sec_properties ] ) . our approach is not fully empirical , because it relies on the semi - empirical results of @xcite and @xcite ; both studies rely on evolution models for the sub - stellar age mass radius relations . however , by adopting the same theoretical evolution models @xcite as in these two studies , our analysis provides a test of the self - consistency of the theoretical models ( [ sec_lt_teff ] ) .

we present the discovery of a brown - dwarf companion to the 130400 myr - old g8 v star hd 203030 . the-band spectral type of l7.5.5 places hd 203030b near the critical l / t transition in brown dwarfs , which is characterized by the rapid disappearance of dust in sub - stellar photospheres . from a comparative analysis with well - characterized field

we present the discovery of a brown - dwarf companion to the 130400 myr - old g8 v star hd 203030 . separated by 11 ( 487 au in projection ) from its host star , hd 203030b has an estimated mass of . the-band spectral type of l7.5.5 places hd 203030b near the critical l / t transition in brown dwarfs , which is characterized by the rapid disappearance of dust in sub - stellar photospheres . from a comparative analysis with well - characterized field l / t transition dwarfs , we find that , despite its young age , hd 203030b has a bolometric luminosity similar to the gyr - old field dwarfs . adopting a radius from current models of sub - stellar evolution , we hence obtain that the effective temperature of hd 203030b is only k , markedly lower than the k effective temperatures of field l / t transition dwarfs . the temperature discrepancy can be resolved if either : ( 1 ) the ages of field brown dwarfs have been over - estimated by a factor of.5 , leading to under - estimated radii , or ( 2 ) the lower effective temperature of hd 203030b is related to its young age , implying that the effective temperature at the l / t transition is gravity - dependent .

0903.4911

i

unravelling the physics of how gas - rich disk galaxies , recently arrived in galaxy clusters , are transformed into the quiescent elliptical and s0 populations that dominate dense cluster cores at @xmath14 is one of the longest - standing unsolved problems in astrophysics . numerous studies of massive early - type galaxies in clusters have revealed predominately old stellar populations with apparently very little growth in stellar mass in massive cluster galaxies since @xmath15 @xcite . this indicates that the majority of stars in cluster early - type galaxies formed at high redshift , @xmath16 . however @xcite found that the fraction of cluster members with blue optical colours increases from zero in the local universe to @xmath17 by @xmath18 , suggesting that the fraction of cluster galaxies that are actively forming stars increases with increasing lookback time . empirically the star - forming spiral galaxies found by @xcite at @xmath19.20.4 are mostly replaced by s0 galaxies in local clusters @xcite . indeed , s0s may be completely absent at @xmath20 @xcite , although @xcite suggest that the s0 fraction remains constant over @xmath21 ( see also * ? ? ? a simple interpretation is that clusters accrete blue gas - rich star - forming spirals at @xmath22.51 and that these galaxies were transformed somehow into the passive s0s found in local clusters . numerous mechanisms have been proposed to deplete the reservoir of gas in late - type spiral galaxies and thus cut off the fuel supply for further star - formation , leading to transformation into s0 galaxies ( for reviews see * ? ? ? * ; * ? ? ? historically most of the work on this area has concentrated on optical wavelengths , for example identifying the so - called e+a galaxies @xcite . these galaxies exhibit deep balmer absorption lines and lack nebular emission lines indicating that these apparently passive galaxies were actively forming stars in the preceding @xmath23.51.5gyr . indeed , simple evolutionary models have been used to connect , via aging and thus fading , this newly quiescent population with actively star - forming spiral galaxies . mid - infrared observations of cluster galaxies with _ iso _ and _ spitzer _ have challenged the idea that all spiral galaxies that fall into clusters simply fade into passive galaxies via an intermediate e+a phase . for example , _ iso _ revealed a population of luminous infrared galaxies ( @xmath24 lirgs ) and near - lirgs in clusters that imply that the star - formation rates derived from optical diagnostics ( e.g. [ oii ] ) under - estimate the true star formation rate ( sfr ) by @xmath2503@xmath26 ( see * ? ? ? * for a review ) . deep radio observations have also revealed that many e+as harbour significant ongoing star - formation missed by optical diagnostics due to heavy dust obscuration @xcite . the simple optically - derived fading of spiral galaxies therefore seems to be substantially incomplete . radio and mid - infrared observations have also revealed an order of magnitude cluster - to - cluster variations in the amount of obscured star formation in clusters @xcite . these differences have broadly been attributed to differences in the recent dynamical history of the clusters ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , however early _ iso _ results had already suggested that a simple one - to - one relationship between cluster - cluster mergers and obscured star formation does not exist . for example , _ iso _ identified 10 lirgs in cl0024 and none in a1689 , a2218 , and a2390 ( coia et al . , 2005b ; see also metcalfe et al . , all four clusters are well known strong lensing clusters , the mass distributions of which are constrained by their strong lensing signal to be multi - modal , i.e. indicative of recent cluster - cluster merging ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? indications of the likely complex relationship between the dynamical state of clusters and their current star - formation rate was also found in the pioneering optical studies . for example , for the coma cluster @xcite found numerous galaxies with post - starburst characteristics ( strong balmer - line absorption ) between the two x - ray peaks corresponding to the main coma cluster and the ngc4839 subcluster , suggestive of starbursts and subsequent quenching resulting from a cluster - cluster merger . in contrast , @xcite found no enhancement in the blue galaxy distribution between the two x - ray peaks for an apparently similar system abell 168 . for this latter case , @xcite suggests that the lack of enhanced star - formation could be due to the galaxies being previously gas - poor and hence unable to be triggered on interaction with their environment . @xcite measured the fraction of cluster galaxies with blue optical colours out to @xmath27 , although their sample was dominated by clusters at @xmath28 . the blue galaxy fractions in these `` intermediate '' redshift clusters span the full range of values found in clusters at @xmath14 and @xmath27 , i.e. @xmath2900.2 . numerous uv / optical , infrared and radio surveys have broadly confirmed that the scatter is large , however none have combined the sample size and multi - wavelength dataset required to relate directly actively star - forming galaxies in clusters to differences in the intracluster medium and recent dynamical history of clusters . the local cluster substructure survey ( locuss ; pi : g. p. smith ; http://www.sr.bham.ac.uk/locuss ) is a systematic multi - wavelength survey of 100 galaxy clusters at @xmath0 drawn from the rosat all sky survey cluster catalogues @xcite . the overall goal of the survey is to probe the relationship between the recent hierarchical infall history of clusters ( as revealed by strong and weak lensing observations ; * ? ? ? * ) and the baryonic properties of the clusters . this results in two complementary aspects of the survey : mass - observable scaling relations @xcite , and evolution of cluster galaxy populations . both of these themes are connected by the aim of measuring and understanding the physical origin of the cluster - to - cluster scatter . this is the first in a series of papers about the first batch of 31 clusters observed by locuss , for which the following data have been gathered : wide - field subaru / suprime - cam imaging , _ hubble space telescope _ wfpc2 and/or acs imaging of the cluster cores , wide - field _ spitzer_/mips @xmath1 maps to match the half degree suprime - cam field of view , _ galex _ near- and far - ultraviolet ( nuv / fuv ) imaging , and wide - field near - infrared ( nir ) imaging obtained via a combination of ukirt / wfcam and kpno-4m / newfirm . we have also been awarded 500ksec on _ herschel _ as an open time key program to observe this sample at @xmath30 and @xmath31 with pacs . the galaxy evolution goals that we will tackle with these data include to measure robustly the scatter in the amount of obscured star formation in clusters at `` low '' redshift @xcite , and to cross - correlate the location of the obscured cluster galaxies with mass over - densities found in the weak - lensing mass maps derived from the subaru data @xcite . full details of the survey design will be given in a future paper , however here we emphasize that at the nominal redshift of our sample , @xmath32 , the suprime - cam field - of - view covers @xmath33 centred on each cluster . a @xmath34 @xcite dark matter halo has a virial radius of @xmath35 . our survey therefore probes out to @xmath36 the virial radius of the clusters . the uv and ir data discussed above all cover at least the same field of view as the subaru data . this survey is therefore sensitive to the infall regions of clusters studied recently by , for example , @xcite and @xcite . in this paper we present an analysis of abell 1758 ( a1758 ) at @xmath2 as a case study on the influence of cluster - cluster mergers on obscured star formation , and to outline the methods that will be applied to the full sample in future papers . a1758 was selected for this study because previous x - ray and lensing studies have identified it as a merging cluster , comprising two gravitationally bound components one to the north and one to the south ( a1758n and a1758s respectively ) both of which are undergoing a merger @xcite . we note that throughout the paper , we describe the star - formation measured from the @xmath1 data as obscured , making no distinction between heavily obscured star - formation or the much less attenuated diffuse emission from normally star - forming spirals as done by @xcite . the most straightforward interpretation @xcite of the @xmath1 emission is that it traces the dust obscured star - formation , while the observed uv or h@xmath37 emission traces the unobscured one @xcite . in future , we will combine uv and ir data to obtain robust measures of both obscured and unobscured star - formation in cluster galaxies , as well as the level of extinction . in [ sec : data ] we describe our observations of a1758 , plus archival data from the xmm - lss field that we use to establish optimal colour selection criteria to identify galaxies at the cluster redshift . in [ sec : analysis ] and [ sec : results ] we present the photometric analysis and the main results respectively . we discuss the results in [ sec : discuss ] and summarize them in [ sec : conc ] . when necessary we assume , and , giving a lookback time of @xmath38 and an angular scale of @xmath39 arcmin@xmath40 at the cluster redshift . all magnitudes are quoted in the vega system unless otherwise stated .

we present the first galaxy evolution results from the local cluster substructure survey ( locuss ) , a multi - wavelength survey of 100 x - ray selected galaxy clusters at . locuss combines far - uv through far - ir observations of cluster galaxies with gravitational lensing analysis and x - ray data to investigate the interplay between the hierarchical assembly of clusters and the evolution of cluster galaxies . here we present new panoramic _ spitzer_/mips observations of the merging cluster abell 1758 at spanning and reaching a completeness limit of . our ongoing far - uv through far - ir observations of a large sample of clusters should allow us to disentangle the different physical processes responsible for triggering obscured star formation in clusters . [ firstpage ] galaxies : active galaxies : clusters : general galaxies : evolution galaxies : stellar content

we present the first galaxy evolution results from the local cluster substructure survey ( locuss ) , a multi - wavelength survey of 100 x - ray selected galaxy clusters at . locuss combines far - uv through far - ir observations of cluster galaxies with gravitational lensing analysis and x - ray data to investigate the interplay between the hierarchical assembly of clusters and the evolution of cluster galaxies . here we present new panoramic _ spitzer_/mips observations of the merging cluster abell 1758 at spanning and reaching a completeness limit of . we estimate a global cluster star - formation rate of within of the cluster centre , originating from 42 galaxies with . the obscured activity in a1758 is therefore comparable with that in cl0024 , the most active cluster previously studied at . the obscured galaxies faithfully trace the cluster potential as revealed by the weak - lensing mass map of the cluster , including numerous mass peaks atmpcthat are likely associated with infalling galaxy groups and filamentary structures . however the core ( ) of a1758n is more active in the infrared than that of a1758s , likely reflecting differences in the recent dynamical history of the two clusters . the 24 results from a1758 therefore suggest that dust - obscured cluster galaxies are common in merging clusters and suggests that obscured activity in clusters is triggered by both the details of cluster - cluster mergers and processes that operate at larger radii including those within in - falling groups . our ongoing far - uv through far - ir observations of a large sample of clusters should allow us to disentangle the different physical processes responsible for triggering obscured star formation in clusters . [ firstpage ] galaxies : active galaxies : clusters : general galaxies : evolution galaxies : stellar content

0903.4911

c

@xcite and @xcite have studied a1758 in detail as a merging cluster using weak lensing and x - ray data respectively . in particular @xcite investigated the thermodynamics of both cluster components . here we compare our results on obscured star - formation in a1758 with the thermodynamics of the intracluster medium , and thus with the likely dynamical state of the cluster . @xcite found no evidence of compressional heating of the intracluster medium ( icm ) in the region between a1758n and a1758s , suggesting that the two clusters have not begun to merge with each other yet , although they may be gravitational bound to each other already . a1758n itself is interpreted as being a large impact parameter merger between two 7kev clusters , one cluster ( to the north - west ) currently moving to the north and the other ( to the south - east ) currently moving to the south - east . in contrast , the merger in a1758s is interpreted as having a much smaller impact parameter with the merger occurring close to the line - of - sight through the cluster . the core radii of the merging components within a1758n are @xmath188 ; in contrast the merging components of a1758s have core radii of @xmath189 and @xmath190 . @xcite therefore suggested that , as a consequence of the differing impact parameters , the galaxies in the merging clusters of a1758s have experienced lower ram pressures than those in a1758n , and that a1758s may be at an earlier stage in its merger than a1758n . however , both a1758n and a1758s do contain regions of hotter gas that have presumably been shock - heated during the respective mergers . the precise timing difference between the two mergers is difficult to ascertain , however @xcite proposed that a1758n is seen significantly after the point of closest approach whilst a1758s may be seen at approximately the epoch of closest approach . okabe & umetsu s weak lensing mass map successfully resolves the two merging components of a1758n , and locates a single mass peak in the core of a1758s , both of which are consistent with david & kempner s interpretation of the x - ray data . how well do our mid - ir results fit with the x - ray and lensing results ? one of the most striking features of the distribution of obscured galaxies in fig . [ fig : spatial ] is their absence from the central @xmath191 region of a1758s , in contrast to the same region in a1758n , especially in the vicinity of the south - east component of a1758n . this difference between the clusters is reminiscent of the large cluster - to - cluster scatter within the core regions of merging clusters found with _ intense star formation can be triggered in cluster - cluster mergers by the passage of gas - rich galaxies through shocked regions of the icm @xcite . in a1758n the merger - induced shock - front(s ) have dissipated @xcite , which helps to explain why shock - fronts are not found adjacent to the dusty galaxies in the core of that cluster . a1758s is claimed to be an earlier stage in the merging process , however @xcite did detect shock - heated gas in this cluster . therefore naively one would expect that star - formation would have been triggered by the shocks as in a1758n . however no @xmath1 sources are found in the central @xmath181 region of a1758s . the merger geometry of a1758s may help to explain the absence of obscured galaxies in its core . for example the @xmath1 sources at @xmath192 may have been scattered to large radii by the line - of - sight merger that is ongoing in the core of the cluster in a manner analogous to the distribution of cluster galaxies in cl0024 , another line - of - sight merger cluster @xcite . assuming that the galaxies are moving at @xmath193 it would take them @xmath194 to travel to a radius of @xmath195 from the centre of the cluster . on the face of it , this is inconsistent with david & kempner s proposal that the sub - clusters in the a1758s merger are approximately at closest approach . an alternative interpretation of the @xmath1 data might be that the shocks in a1758s were not strong enough to trigger detectable star - formation in the cluster galaxies that passed though them . we also note that a1758s is much less optically rich than a1758n , so the absence of obscured activity in a1758s could simply be due to a1758s being a poorer cluster than a1758n . this is supported by fig . [ bo ] because the fraction of star - forming @xmath1-bright galaxies in both clusters is consistent within the errors . in summary , our mid - ir results are qualitatively consistent with the previous x - ray and lensing results . however the absence of obscured galaxies in the core of a1758s remains a puzzle . one possibility is that the galaxies were already gas - poor before the cluster merger , and hence had no available fuel to undergo new star - formation . our results confirm and extend the view formed from _ iso _ that the cluster - to - cluster scatter in merging clusters is large , and likely related to the physical parameters of cluster mergers . the global sfr of a1758 estimated from the @xmath1 flux of photometrically selected members is @xmath128 , qualifying it as one of the most infrared active clusters studied to date . for example it is comparable with the most active cluster studied to date cl0024 at @xmath196 with @xmath197 @xcite . globally this is unsurprising because a1758 contains two ongoing cluster - cluster mergers and one ( between a1758n and a1758s ) that may occur within a few gyr . however the picture is more subtle when considering the specific sfr ( @xmath198 ) and star - forming fraction of galaxies ( @xmath199 see figs . [ geach ] & [ bo ] respectively ) . cl0024 stands out in fig . [ geach ] as the most active cluster by a factor of @xmath200 in @xmath198 because of it s low mass relative to a1758 . on the other hand , cl0024 and a1758 have comparable values of @xmath201 ( fig . [ bo ] ) , indicative of the clusters having comparable optical richness . this further underlines the conclusion that numerous parameters influence the level of obscured star - formation in galaxy clusters : merger geometry , density of the icm , location of shock - heated gas with respect to the cluster galaxies , the available supply of gas in cluster galaxies in which star - formation may be triggered by shock - heating of the icm , the optical richness of the cluster , and cluster mass . we will investigate these issues in detail with the full sample in a future paper . we find a significant population of passive spiral galaxies , defined empirically by @xmath182 , @xmath165 and @xmath202 . the radial distribution of these galaxies is intermediate in radial extent between the cluster early - types and the actively star - forming galaxies detected at @xmath1 ( fig . [ fig : radial ] ) . if the radial extent of each distribution indicates the length of time that each population has on average spent in the cluster potential well , then the passive spirals have been accreted by a1758 less recently than the actively star - forming galaxies . a simple interpretation is therefore that the passive spirals were formerly actively forming stars and thus brighter at @xmath1 , i.e. that there is an evolutionary path linking the dusty star - forming galaxies , passive spirals and cluster early - type galaxies ( see e.g. * ? ? ? @xcite identified a significant population of passive spirals in cl0024 over a wide range of environments , and used a combination of _ galex _ uv photometry and optical spectroscopy to find that their star - formation quenching time - scales are often @xmath203 , suggestive more of starvation , although the rapid quenching expected for ram - pressure stripping was also observed . as the simulations of @xcite show , gas is lost from infalling galaxies over a wide range of environments ( even beyond the virial radius ) on both short and long time - scales , and @xcite estimate that the observed frequency and quenching time - scales of passive spirals in @xmath204 clusters could account for the entire build - up of s0s between @xmath205 and @xmath206 . the relationship between moran et al.s uv / optical selected passive spirals and our optical / ir selected passive spirals is currently unclear . for example , the evolutionary path outlined above may not include the uv / optical passive spirals discussed by @xcite . on the other hand , if the two populations of passive spirals are indeed the same class of object , then the evolutionary path may not be valid . in that case an alternative interpretation of the differing radial distributions of dusty and passive spirals could be that the physical processes that trigger star formation in the former population are more efficient at the largest radii than the processes that act to quench star formation in the latter population . the _ galex _ , _ spitzer _ , _ herschel _ , ground - based near - ir photometry and optical spectroscopy dataset that we are assembling on a large sample of clusters will be very powerful for disentangling the respective galaxy populations .

the obscured galaxies faithfully trace the cluster potential as revealed by the weak - lensing mass map of the cluster , including numerous mass peaks atmpcthat are likely associated with infalling galaxy groups and filamentary structures . the 24 results from a1758 therefore suggest that dust - obscured cluster galaxies are common in merging clusters and suggests that obscured activity in clusters is triggered by both the details of cluster - cluster mergers and processes that operate at larger radii including those within in - falling groups .

we present the first galaxy evolution results from the local cluster substructure survey ( locuss ) , a multi - wavelength survey of 100 x - ray selected galaxy clusters at . locuss combines far - uv through far - ir observations of cluster galaxies with gravitational lensing analysis and x - ray data to investigate the interplay between the hierarchical assembly of clusters and the evolution of cluster galaxies . here we present new panoramic _ spitzer_/mips observations of the merging cluster abell 1758 at spanning and reaching a completeness limit of . we estimate a global cluster star - formation rate of within of the cluster centre , originating from 42 galaxies with . the obscured activity in a1758 is therefore comparable with that in cl0024 , the most active cluster previously studied at . the obscured galaxies faithfully trace the cluster potential as revealed by the weak - lensing mass map of the cluster , including numerous mass peaks atmpcthat are likely associated with infalling galaxy groups and filamentary structures . however the core ( ) of a1758n is more active in the infrared than that of a1758s , likely reflecting differences in the recent dynamical history of the two clusters . the 24 results from a1758 therefore suggest that dust - obscured cluster galaxies are common in merging clusters and suggests that obscured activity in clusters is triggered by both the details of cluster - cluster mergers and processes that operate at larger radii including those within in - falling groups . our ongoing far - uv through far - ir observations of a large sample of clusters should allow us to disentangle the different physical processes responsible for triggering obscured star formation in clusters . [ firstpage ] galaxies : active galaxies : clusters : general galaxies : evolution galaxies : stellar content

0903.4911

c

we have presented the first results from our panoramic multi - wavelength survey of 31 clusters at @xmath207 clusters as part of the local cluster substructure survey ( locuss ; pi : g. p.smith ) . for this initial study we chose a1758 , an actively merging cluster at @xmath152 that has been previously studied with high quality weak lensing and x - ray data @xcite . specifically , we have combined a wide - field ( @xmath208 ) _ spitzer_/mips @xmath1 map of the entire a1758n / a1758s complex with panoramic @xmath65-band imaging from ukirt / wfcam and archival optical data from subaru to map out the locations of dusty star - forming galaxies in addition to cluster early - types and cluster spirals that are undetected down to @xmath5 . the main results are as follows : \(i ) we detect 82 probable cluster members in the mid - ir with _ spitzer_/mips at @xmath1 within 3mpc of the cluster centre . after correcting for residual field contamination using archival data from the xmm - lss , we measure an excess of 42 mid - ir sources over the field counts with @xmath84 , responsible for a total flux of @xmath209 . \(ii ) adopting @xcite s ( @xcite ) sed templates , we convert our 90% completeness limit of @xmath5 into a luminosity sensitivity of @xmath210 i.e. sub - lirg luminosities . most of the ir - luminous cluster sources appear to be sub - lirgs . we estimate there to be 10 lirgs within 3mpc of the cluster centre , comparable to the number in cl0024 . we identify just one possible cluster ulirg ( @xmath155 ) , which appears to be a merging galaxy system with a combined nir luminosity of @xmath211 . \(iii ) we also convert the total cluster flux at @xmath1 to a total cluster star formation rate of @xmath212 . this is consistent within the errors with the most active cluster studied to date : cl0024 @xcite . we split the @xmath1 sources between the a1758n and a1758s based the proximity of each galaxy to the respective cluster centres , to obtain @xmath213 and @xmath214 respectively i.e. a1758n is almost twice as active as a1758s . \(iv ) when the level of obscured activity is normalized to the mass and the optical richness of the cluster , then we find that the specific star - formation rate of a1758 is lower than that of cl0024 and that the fraction of cluster galaxies that are detected at @xmath1 is comparable with cl0024 . these results reflect the facts that a1758 is more massive than and of comparable richness to cl0024 . \(v ) dust - obscured galaxies with late - type morphologies are detected in a network of infalling groups and filamentary structures that surround both a1758n and a1758s that is delineated by the reconstructed cluster mass distribution from @xcite . however in the core regions of each cluster we find that the central @xmath11 region of a1758n is comparatively rich in dusty galaxies in contrast to the absence of such objects in the same region of a1758s . this difference may be due to the differing recent dynamical histories of the two clusters , as discussed by @xcite . \(vii ) finally , we identify a population of ir - selected passive spiral galaxies , i.e. they have a late - type morphology and are undetected at @xmath1 . the radial distribution of these galaxies does not extend as far as that of the mips - detected population , suggesting that they were accreted into the cluster potential on average longer ago than the active dusty population . however the difference in radial distribution may also indicate that they are a distinct population in transition from spiral to early - type morphology , and that they are affected by different physical process than the dusty galaxies . comparison of these ir passive spirals with uv - selected passive spirals will help to clarify the status of both populations . the next steps in this study are to repeat this analysis for a large ( @xmath215030 ) sample of clusters in order to measure for the first time the scatter in the infrared properties of clusters . the biggest caveat on our results is the reliance on photometry to select cluster galaxies . we will therefore also significantly enhance the precision of our analysis as spectroscopic redshifts become available from our ground - based optical spectroscopic observations recently commenced with hectospec at the mmt . we also plan to integrate this optical / near - ir / mid - ir analysis with our _ galex _ observations of the same clusters , and _ herschel _ data when they become available . the overall goal is to pinpoint the contribution that the various physical processes make to the transformation of gas rich spiral galaxies into early - type cluster galaxies via a large and detailed study of clusters in a single redshift slice .

the obscured activity in a1758 is therefore comparable with that in cl0024 , the most active cluster previously studied at . however the core ( ) of a1758n is more active in the infrared than that of a1758s , likely reflecting differences in the recent dynamical history of the two clusters .

we present the first galaxy evolution results from the local cluster substructure survey ( locuss ) , a multi - wavelength survey of 100 x - ray selected galaxy clusters at . locuss combines far - uv through far - ir observations of cluster galaxies with gravitational lensing analysis and x - ray data to investigate the interplay between the hierarchical assembly of clusters and the evolution of cluster galaxies . here we present new panoramic _ spitzer_/mips observations of the merging cluster abell 1758 at spanning and reaching a completeness limit of . we estimate a global cluster star - formation rate of within of the cluster centre , originating from 42 galaxies with . the obscured activity in a1758 is therefore comparable with that in cl0024 , the most active cluster previously studied at . the obscured galaxies faithfully trace the cluster potential as revealed by the weak - lensing mass map of the cluster , including numerous mass peaks atmpcthat are likely associated with infalling galaxy groups and filamentary structures . however the core ( ) of a1758n is more active in the infrared than that of a1758s , likely reflecting differences in the recent dynamical history of the two clusters . the 24 results from a1758 therefore suggest that dust - obscured cluster galaxies are common in merging clusters and suggests that obscured activity in clusters is triggered by both the details of cluster - cluster mergers and processes that operate at larger radii including those within in - falling groups . our ongoing far - uv through far - ir observations of a large sample of clusters should allow us to disentangle the different physical processes responsible for triggering obscured star formation in clusters . [ firstpage ] galaxies : active galaxies : clusters : general galaxies : evolution galaxies : stellar content

0910.5666

i

compared to known superbubbles and hii regions ic131-se appears to be peculiar with respect to its lopsided x - ray morphology , the large linear extent of the x - ray emission , the lack of massive o stars , its high electron temperature ( in case the x - ray gas is thermal ) , and large fraction of hard x - rays . the x - ray spectrum of the extended emission in ic131-se can be equally well fitted by an absorbed power law ( @xmath207 ) or an absorbed thermal plasma model ( @xmath208kev ) . these models predict a total ( 0.358.0kev ) unabsorbed x - ray luminosity of about @xmath209erg s@xmath5 and @xmath210erg s@xmath5 , respectively , with 39% and 53% of the luminosity being emitted above 2kev . apparently ic131 possesses not only the hardest x - ray spectrum among the known ghrs , but , in case the gas is thermal , also the hottest x - ray plasma . besides the facts that thermal x - ray emission is expected from ghrs and that there might be weak emission lines below 1kev , the disagreement between the number of sne progenitors obtained from the imf ( 921 ) and that derived from the internal thermal energy ( 118@xmath9959 ) argues against a pure thermal origin of the gas . we estimate a low electron density of @xmath211@xmath79 ( assuming @xmath212 ) and an x - ray gas mass of about 3300@xmath7 . the age of the stellar population inside the bubble seems to range from 8 to 77myr and given a cooling timescale of about 1gyr , the gas did not have time to cool significantly . if the gas is thermal , the standard bubble models require shocks from snrs and sne to heat the gas . the fundamental problem which argues against a thermal plasma is that we are not aware of a mechanism for ghrs which can produce electron temperatures anywhere close to @xmath213kev . non - thermal x - ray emission is also known to originate from snrs , ghrs or superbubbles and the spectral power law fit is statistically as good as the one for a thermal plasma . synchrotron emission as opposed to inverse compton scattering is a plausible mechanism for the assumed magnetic field strength of @xmath214 and the total energy of the relativistic synchrotron - emitting electron population is about 14% to 30% of the total energy provided by sne . if a non - thermal component exists , synchrotron losses clearly dominate over losses from inverse compton scattering . for a purely non - thermal origin , however , it remains to be investigated what kinds of mechanisms are able to produce non - thermal x - rays or accelerate particles to relativistic energies on scales of 200pc . to allow for a more quantitative analysis of the non - thermal x - ray emission , models are required which predict the fraction of non - thermal radiation from ghrs . a combined thermal and non - thermal model seems to be generally appropriate , too , irrespective of the unreasonably high column density and x - ray luminosity derived from those fits . unfortunately , with the present data the nature of the extended x - ray emission can not be conclusively determined . clearly , ic131-se is an important object and challenges the standard bubble model as well as our understanding of cr acceleration in superbubbles . it is remarkable and remains to be understood why objects similar to ic131-se have not been detected before . future investigations would greatly profit from more sensitive and deeper x - ray observations ( as for example provided by ixo ) , high - resolution optical spectrophotometric data , and models which can explain electron temperatures @xmath111kev and make predictions on the non - thermal x - ray emission in ghrs . the deeper x - ray observations could establish the presence of x - ray emission lines and settle the question on the nature of the emission , while a detailed stellar population analysis could provide a more accurate imf . clearly , ngc604 and ic131-se seem to be in completely different evolutionary stages . all o - type stars in ic131-se seem to have exploded as sne , whereas the western part of ngc604 awaits the first sne to occur . we detect only one x - ray point source in ic131 . this source , cxoj013315.10 + 304453.0 ( fl073 ) , appears to be time variable and is possibly a hmxrb with an optical counterpart which could be a b2v star with a mass of about 9m@xmath102 . this work has made use of saoimage ds9 @xcite , developed by the sao , the funtools utilities , and the heasarc ftools package . we thank the anonymous referee for useful comments which helped to improve the paper . rt acknowledges support under nasa _ chandra _ award number go6 - 7073a . acknowledges support through g06 - 7073c . tjg and ppp acknowledge support under nasa contract nas8 - 03060 . arnaud , k. a. 1996 , astronomical data analysis software and systems v , eds . g. jacoby and j. barnes , asp conf . series , 101 , 17 bamba , a. , ueno , m. , nakajima , h. , & koyama , k. 2004 , , 602 , 257 bell , a. r. 1978 , , 182 , 147 broos , p. s. , townsley , l. k. , getman , k. , & bauer , f. e. 2002 , acis extract , an acis point source extraction package ( university park : pennsylvania state univ . ) butt , y. m. , & bykov , a. m. 2008 , , 677 , l21 buneman , o. 1958 , phys . , 115 , 503 chen , y. , seward , f. d. , sun , m. , & li , j .- 2008 , , 676 , 1040 cooper , r. l. , guerrero , m. a. , chu , y .- h . , chen , c .- h . r. , & dunne , b. c. 2004 , , 605 , 751 dickey , j. m. , & lockman , f. j. 1990 , , 28 , 215 freedman , w. l. , madore , b. f. , gibson , b. k. , ferrarese , l. , kelson , d. , et al . 2001 , , 553 , 47 gonzlez delgado , r. m. , & prez , e. 2000 , , 317 , 64 haberl , f. , & pietsch , w. 2001 , , 373 , 438 hartman , j. d. , bersier , d. , stanek , k. z. , beaulieu , j .- p . , kaluzny , j. , marquette , j .- b . , stetson , p. b. , & schwarzenberg - czerny , a. 2006 , , 371 , 1405 helder , e. a. , & vink , j. 2008 , , 686 , 1094 hippelein , h. , haas , m. , tuffs , r. j. , lemke , d. , stickel , m. , klaas , u. , vlk , h. j. 2003 , , 407 , 137 hughes , j. p. , rakowski , c. e. , & decourchelle , a. 2000 , , 543 , l61 hunter , d. a. , baum , w. a. , oneil , e. j. , jr . , & lynds , r. 1996 , , 456 , 174 joye , w. a. , & mandel , e. 2003 , astronomical data analysis software and systems xii , eds . e. payne , r. i. jedrzejewski , and r. n. hook , asp conference series , 295 , 489 katsuda , s. , petre , r. , hwang , u. , yamaguchi , h. , mori , k. , & tsunemi , h. 2009 , arxiv:0902.1782 kennicutt , r. c. , jr . 1984 , , 287 , 116 koyama , k. , petre , r. , gotthelf , e. v. , hwang , u. , matsuura , m. , ozaki , m. , & holt , s. s. 1995 , , 378 , 255 kroupa , p. 2001 , , 322 , 231 laming , j. m. , raymond , j. c. , mclaughlin , b. m. , & blair , w. p. 1996 , , 472 , 267 landsman , w. b. , roberts , m. s. , bohlin , r. c. , oconnell , r. w. , smith , a. m. , & stecher , t. p. 1992 , , 401 , l83 long , k. s. , charles , p. a. , blair , w. p. , & gordon , s. m. 1996 , , 466 , 750 long , k. s. , reynolds , s. p. , raymond , j. c. , winkler , p. f. , dyer , k. k. , r & petre , r. 2003 , , 586 , 1162 longair , m. s. 1994 , high energy astrophysics , volume 2 , 2nd edition , cambridge university press lesch , h. 1990 , , 239 , 437 maclow , m .- m . , & mccray , r. 1988 , , 324 , 776 maddox , l. a. , williams , r. m. , dunne , b. c. , & chu , y .- h . 2009 , , 699 , 911 maeder , a ; , & meynet , g. 1994 , a&a , 287 , 803 malkov , m. a. , & oc drury , l. 2001 , reports on progress in physics , 64 , 429 massey , p. , olsen , k. a. g. , hodge , p. w. , strong , s. b. , jacoby , g. h. , schlingman , w. , & smith , r. c. 2006 , , 131 , 2478 mccray , r. , & kafatos , m. 1987 , , 317 , 190 misanovic , z. , pietsch , w. , haberl , f. , ehle , m. , hatzidimitriou , d. , & trinchieri , g. 2006 , , 448 , 1247 mcbride , v. a. , coe , m. j. , negueruela , i. , schurch , m. p. e. , & mcgowan , k. e. 2008 , , 388 , 1198 muno , m. p. , law , c. , clark , j. s. , dougherty , s. m. , de grijs , r. , portegies zwart , s. , & yusef - 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interscience ) sutherland , r. s. , & dopita , m. a. 1993 , , 88 , 253 tabatabaei , f. s. , beck , r. , krgel , e. , krause , m. , berkhuijsen , e. m. , gordon , k. d. , & menten , k. m. 2007 , , 475 , 133 tanaka , y. 2002 , , 382 , 1052 tang , s. , & wang , q. d. 2002 , , 628 , 205 townsley , l. k. , broos , p. s. , feigelson , e. d. , brandl , b. r. , chu , y .- h . , garmire , g. p. , & pavlov , g. g. 2006 , , 131 , 2140 tllmann , r. , gaetz , t. j. , plucinsky , p. p. , long , k. s. , hughes , j. p. , et al . 2008 , , 685 , 123 vilchez , j. m. , pagel , b. e. j. , diaz , a. i. , terlevich , e. , & edmunds , m. g. 1988 , , 235 , 633 wang , q. d. 1999 , , 510 , l139 weaver , r. , mccray , r. , castor , j. , shapiro , p. , & moore , r. 1977 , , 218 , 377 williams , b. f. , et al . 2008 , , 680 , 1120 wilms , j. , allen , a. , & mccray , r. 2000 , , 542 , 914 wolk , s. j. , bourke , t. l. , smith , r. k. , spitzbart , b. , & alves , j. 2002 , , 580 , l161 woosley , s. e. , heger , a. , & weaver , t. a. 2002 , rvmp , 74 , 1015 yamaguchi , h. , bamba , a. , & koyama , k. 2009 , , 61 , 175

known hii regions ic131-se seems to be extreme regarding the combination of its large extent of the x - ray plasma , the lack of massive o stars , its unusually high electron temperature ( if thermal ) , and the large fraction of emitted above 2kev (% ) . if the gas is non - thermal or has non - thermal contributions , synchrotron emission would clearly dominate over inverse compton emission . we also detect a variable source candidate in ic131 .

we present the first x - ray analysis of the diffuse hot ionized gas and the point sources in ic131 , after ngc604 the second most x - ray luminous giant hii region in m33 . the x - ray emission is detected only in the south eastern part of ic131 ( named ic131-se ) and is limited to an elliptical region of pc in extent . this region appears to be confined towards the west by a hemispherical shell of warm ionized gas and only fills about half that volume . although the corresponding x - ray spectrum has 1215 counts , it can not conclusively be told whether the extended x - ray emission is thermal , non - thermal , or a combination of both . a thermal plasma model of=4.3kev or a single power law of.1 fit the spectrum equally well . if the spectrum is purely thermal ( non - thermal ) , the total unabsorbed x - ray luminosity in the 0.358kev energy band amounts toerg s . among other known hii regions ic131-se seems to be extreme regarding the combination of its large extent of the x - ray plasma , the lack of massive o stars , its unusually high electron temperature ( if thermal ) , and the large fraction of emitted above 2kev (% ) . a thermal plasma ofkev poses serious challenges to theoretical models , as it is not clear how high electron temperatures can be produced in hii regions in view of mass - proportional and collisionless heating . if the gas is non - thermal or has non - thermal contributions , synchrotron emission would clearly dominate over inverse compton emission . it is not clear if the same mechanisms which create non - thermal x - rays or accelerate crs in snrs can be applied to much larger scales of 200pc . in both cases the existing theoretical models for giant hii regions and superbubbles do not explain the hardness and extent of the x - ray emission in ic131-se . we also detect a variable source candidate in ic131 . it seems that this object is a high mass x - ray binary whose optical counterpart is a b2-type star with a mass of .

1312.4526

i

galaxy clusters are the largest and youngest gravitationally - bound cosmic structure and form hierarchically through collisions and mergers of smaller systems . spatial and radial velocity distributions of member galaxies and x - ray observations of the intracluster medium ( icm ) have revealed that some systems are still forming and unrelaxed . along with gravitational lensing observations , these studies have provided dynamical measurements of dark matter in clusters . as the structure forms , gravitational potential governed by dark matter pulls and thus heats the icm through shocks . sharp x - ray images obtained by _ chandra _ revealed shocks and density discontinuities ( so - called `` cold fronts '' ) suggesting supersonic or transonic gas motions , respectively ( see * ? ? ? * for a review ) . these heating processes would then develop gas turbulence , and accelerate particles , which in turn generate diffuse radio halos and relics . the activities of central massive black holes also disturb and warm up the gas around cluster cores . the motion of gas should be measured to facilitate direct understanding of these energy flows . constraining total energy distribution in a system allows the total gravitational mass to be measured , as required for precise cosmology . energies in gas random or ordered motions could be the key uncertainty to calibrate total mass distribution , as suggested by numerical simulations ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? . gas bulk or turbulent motions can be measured directly using the doppler shift or by broadening of x - ray line emissions . however , the limited energy resolutions of current x - ray instruments continues to hinder such measurements . for example typical ccd energy resolution is about 130 ev ( in full width half maximum ; fwhm ) , compared with a possible energy shift of @xmath4 ev corresponding to a radial velocity of 1000 km s@xmath1 , all at the fe - k line energy . the _ suzaku _ xis @xcite is currently the optimal x - ray spectrometer for gas motion search with fe - k lines , as was demonstrated when gas bulk motion was detected in a merging cluster , abell 2256 , by @xcite . in addition , xis data imposed tight constraints on gas motion in a number of clusters , as summarized in table [ tbl : suzaku - res ] . lll centaurus & @xmath5 km s@xmath1 & 1 + oph . & @xmath6 km s@xmath1 & 2 + amw 7 & @xmath7 km s@xmath1 & 3 + a 2319 & @xmath8 km s@xmath1 & 4 + a 2256 & @xmath9 km s@xmath1 & 5 + coma & @xmath8 km s@xmath1 & 6 + a 3627 & @xmath10 km s@xmath1 & 7 + numerical studies have striven to clarify cluster formation histories and the associated origins , development , and dissipation of various types of gas motions . however , by nature cluster evolution is governed by random processes , which means systematic measurements of systems in a wide range of evolution stages are also required as well as these theoretical efforts . the geometrically - complex nature of gas dynamics should be spatially resolved . for example , gas dynamics in apparently relaxed clusters should be studied as demonstrated by ( * ? ? ? * hereafter ota07 ) using early _ suzaku _ observations of the centaurus cluster . to improve the limit of gas bulk motion in a relaxed system , we analyzed a large set of _ suzaku _ data of the perseus cluster . the perseus cluster , the brightest in x - ray , is a prototype of a nearby and relaxed object . at the same time , it exhibits a number of past and current activities at core and larger scales , while at the cluster center , the very peculiar central galaxy ngc 1275 displays a complex network of emission - line nebulosity . based on the thread - like structure of filaments resolved by the hubble space telescope , @xcite suggested the magnetic support of the structure and ordered gas motions not highly turbulent over scales of @xmath11 kpc around the galaxy . the cluster x - ray emission peaks sharply toward the galaxy and its central active galactic nucleus ( agn ) , 3c 84 . the agn also develops jets and radio lobes where high - energy particles and x - ray - emitting - hot gas interact , as discovered by @xcite . associated with these current and possibly past agn activities , fine gas structures such as bubbles , ripples , and weak shock fronts were revealed by deep _ _ imaging ( * ? ? ? * and references therein ) . these processes dissipate energies into various types of gas motions . independently , based on the lack of resonant scattering of fe - k line emissions , @xcite suggested gas motions in the core of a velocity of at least half the speed of sound . west of ngc 1275 , a chain of galaxies is distributed toward another radio galaxy ic 310 , while other member galaxies and clusters virtually aligned with this chain form the pisces - perseus supercluster . on the other hand , the icm x - ray emission has been traced up to at least 2 mpc with an elongation in the east - west direction . based on the x - ray morphology of early observations , @xcite hypothesized that the gas and galaxies are rotating with a velocity of close to 3000 km s@xmath1 . @xcite found asymmetrical icm temperature distribution and suggested a past merger in the direction parallel to the line of sight . using _ xmm - newton _ @xcite further studied the asymmetric structures around the core ( @xmath12 ) and revealed a hot `` horseshoe '' surrounding the cool core . they also assumed a minor merger along the east - west direction in the sky plane . @xcite studied the gas distribution over wider spatial scale ranges and suggested mergers and associated swirling gas motions . the cluster center has been observed twice - yearly as a calibration target of the xis and we used all available data . the integrated deep exposure of this unique object along with the high sensitivity of the xis provides one of the best quality x - ray spectra from clusters . we also used some offset region ( @xmath13 ) data and derived larger scale icm emission properties . parts of the _ suzaku _ perseus data set were used for a number of measurements . @xcite reported the first detection of cr and mn x - ray lines from clusters and icm elemental abundance measurements , while @xcite and @xcite reported abundance measurements out to the cluster outskirt . using offset xis data along with the hxd data , @xcite reported an upper temperature limit in the outer region . @xcite measured large - scale gas thermal distribution over the viral radius . in the next section , we describe observations and data reduction , while in section [ cal ] we evaluate the accuracy of the xis energy response , which is crucial to calibrate our measurement . in sections [ sect : ana - center ] and [ ana - large ] we measure gas bulk velocities within the central pointing and over a larger scale respectively , for the first time in this system , which enables one of the most accurate measurements of gas bulk motion in relaxed clusters . finally these results are summarized and discussed in the last section . throughout this paper , we assume the flowing cosmological parameters : @xmath14 km s@xmath1mpc@xmath1 , @xmath15 , and @xmath16 . at the cluster redshift of 0.0183 , one arcmin corresponds to 22.2 kpc . we use the 68% ( @xmath17 ) confidence level for errors , unless otherwise stated .

we present the results from _ suzaku _ observations of the perseus galaxy cluster , which is relatively close , the brightest in the x - ray sky and a relaxed object with a cool core . a number of exposures of central regions and offset pointing with the x - ray imaging spectrometer cover a region within radii of . these deep and well - calibrated data are used to measure x - ray redshifts of the intracluster medium . no other velocity structure was discovered . over spatial scales of 50100 kpc and within 200 these x - ray redshift distributions are compared spatially with those of optical member galaxies for the first time in galaxy clusters . based on x - ray line widths gas turbulent velocities within these regions these results of gas dynamics in the core and larger scales in association with cluster merger activities are discussed and future potential of high - energy resolution spectroscopy with astro - h is considered .

we present the results from _ suzaku _ observations of the perseus galaxy cluster , which is relatively close , the brightest in the x - ray sky and a relaxed object with a cool core . a number of exposures of central regions and offset pointing with the x - ray imaging spectrometer cover a region within radii of . the central data are used to evaluate the instrumental energy - scale calibration with accuracy confirmed to within around 300 km s by the spatial and temporal variation of the instruments . these deep and well - calibrated data are used to measure x - ray redshifts of the intracluster medium . a hint of gas bulk motion , with radial velocity of about km s relative to the main system was found at arcmin ( 4590 kpc ) west of the cluster center , where an x - ray excess and a cold front were found previously . no other velocity structure was discovered . over spatial scales of 50100 kpc and within 200 kpc radii of the center , the gas - radial - velocity variation is below 300 km s , while over scales of 400 kpc within 600 kpc radii , the variation is below 600 km s . these x - ray redshift distributions are compared spatially with those of optical member galaxies for the first time in galaxy clusters . based on x - ray line widths gas turbulent velocities within these regions are also constrained within 10003000 km s . these results of gas dynamics in the core and larger scales in association with cluster merger activities are discussed and future potential of high - energy resolution spectroscopy with astro - h is considered .

astro-ph9907371

r

in table [ coords ] we list new hh objects identified by our narrow band ccd imaging of candidates identified from the orion plate . several of the new objects were identified by reipurth ( 1985 ) as candidate hh objects from his eso r film survey of the orion region . objects independently discovered by the ccd imaging of reipurth , bally & devine ( 1998 ; hereafter r98 ) are indicated . in addition to brief comments about their nature and location , table [ coords ] also suggests possible energy sources based on evidence presented . our survey region of the southern portion of l1630 is shown in fig . [ orionb ] . the rest of the cloud complex extends several degrees to the north east of the figure . a diffuse shell of emission and a network of bright rimmed cometary globules surrounds the multiple ob system @xmath15 ori . ogura & sugitani ( 1998 ) list many of these globules as remnant clouds which may be sites of retarded star formation . the bright hii regions ngc2024 and ic434 ( which includes the horsehead nebula ) outlines an ionisation front between the southern portion of l1630 and @xmath15 ori . this ionisation front extends towards the open cluster ngc1981 which approximately marks the division between l1630 and l1641 . the position of the new hh flows in the region are indicated . located on the north western outskirts of ic434 , the bright rimmed cometary globule ori i2 is host to the low luminosity ( l@xmath16 = 13 ) iras source 05355 - 0416 , which drives both a bipolar co and near infrared molecular hydrogen outflow ( sugitani et al . 1989 ; cernicharo et al . 1992 ; hodapp 1994 ) . the iras source is also associated with a h@xmath6o maser ( wouterloot & walmsley 1986 ; codella et al . 1995 ) . a comparison between our scanned and ivn images ( figs [ oi2opt]a , b ) identifies a chain of emission line objects ( objects 25 ) extending to the east of the globule . to the west , we see another emission line feature ( object 1 ) which appears as an extension of faint emission seen in the ivn image . the images ( figs [ oi2ccd]a , b ) confirms the presence of a hh flow , designated here as hh289 . in the central part of the globule , our and h@xmath6 images ( figs [ oi2ccd]b , c ) show two faint knots ( hh289 a / b ) which mirror the position of the h@xmath6 emission . with the exception of knot c , all knots appear bright . knots d f show large arc like morphologies which open towards the iras source . this gives the impression of a bubble surrounding the eastern side of the globule which may represent an interface between the outflow and the uv radiation field from @xmath17 ori , which is 42 to the east of ori i2 . from the distribution of optical and near infrared emission about the iras source ( figs [ oi2ccd]b , c ) , we suggest it is the driving source of the hh289 outflow . the chain extends 551 from the iras source making the lobe 1.23pc in projection . this puts the ori i2 flow in the class of parsec scale flows from low mass stars ( reipurth , bally & devine 1997 ) . as hh objects typically display tangential velocities in the order of 150 ( i.e. , mundt 1988 ) , the age span of the optical knots ranges from 530 yr ( knot a ) , to 8100 yr ( knot f ) . the projected lengths of the ( redshifted ) co , h@xmath6 and optical hh flows are 40 ( 0.09pc ) , 80 ( 0.18pc ) and 551(1.23pc ) respectively . apart from knot a , we do not see any evidence of hhemission associated with the blueshifted co lobe , which we expect will be very faint due to the tenuous medium on the western side of the globule . deeper , and/or images of the western side of the globule may reveal fainter emission . in fig . [ oi2ccd]b , we note the appearance of a tube like feature extending out of the western side of the globule ( object 1 in fig . [ oi2opt]a ) . it is well aligned and mirrors the inner and h@xmath6 knots with respect to the iras source . as this feature is visible on our schmidt images , the emission is most probably scattered light reflected off the walls of the cavity formed by the outflow as it bores its way out of the globule . using aao / ukst material , we have identified a similar feature associated with the cometary globule and outflow complex cg30/hh120 ( zealey et al . the streamer extends to the south west of the globule and appears to be the optical counterpart of an extensive h@xmath6 filament associated with the infrared source cg30irs1 . the tube like feature in ori i2 and the streamer in cg30 may represent limb brightened cavities . located in the vicinity of @xmath15 ori ( fig . [ orionb ] ) , v510 ori (= hbc 177 ) was first classified as a t tauri star based on an objective prism survey of the orion region by sanduleak ( 1971 ) . cohen & kuhi ( 1979 ) list the star as a classical t tauri star ( ctts ) with w ( ) @xmath9 10 . the emission line survey of wiramihardja et al . ( 1991 ) found the source to be a strong emitter with _ v _ = 14.6 mag as opposed to _ v _ = 13.54 mag found by mundt & bastian ( 1980 ) . by use of material , the first optical detection of the v510 ori jet ( parker & phillipps 1998b ; this paper ) is shown in fig . [ v510ccd]a . the jet has previously been identified by long slit spectroscopic studies ( jankovics , appenzeller & krautter 1983 ; hirth , mundt & solf 1997 ) . the scanned image ( fig . [ beori]a ) reveals a highly collimated jet . several faint knots ( a c ) are located 57 , 84and 194 from v510 ori . the flow terminates at the large bow shock structure hh444d , which displays wide wings which sweep back towards to position of v510 ori . the image ( fig . [ v510ccd]b ) clearly identifies the hh444 jet extending from v510 ori . due to the seeing conditions at the time ( @xmath8 3 ) , we can only confirm the presence of knots b and d in the image . for the continuum frame ( fig . [ v510ccd]c ) , conditions were slightly better and based on the scanned and continuum image , knots a c are considered as pure emission line features . the jet appears as two separate parts , with the first section appearing as a dense region extending 10from v510 ori , while a second , more fainter part extends a further 6 . this change may represent several individual condensations not resolved by our images . the total projected length of the optical flow is 0.6pc in length . the small separation between v510 ori and its jet implies the jet is still active today and coupled with the fact that we do not see an obvious counter flow suggests an evolved case of a one sided jet ( rodrguez & reipurth 1994 ) . high resolution optical and near infrared studies of the jet and energy source will be beneficial in determining the nature of this unusual outflow complex . as shown in fig . [ oriona ] , the northern border of l1641 is approximated by the bright ionisation front near the open cluster ngc1981 . the cloud extends several degrees south of the figure . the emission surrounding the bright hii region m42 shows remarkable substructure . the southern portion of the image is bounded by the bright reflection nebulosity ngc1999 . in contrast to the l1630 region , we have identified 15 hhcomplexes within the outlined region shown in fig . [ oriona ] . the region is shown in more detail in fig . [ strings ] , where the new objects and features of note are indicated . several strings of objects appear to extend to the north and north east of the figure . the outlined region towards the centre of fig . [ strings ] contains a cluster of objects surrounding the high luminosity source iras 053380624 ( l@xmath16 @xmath8 220 ) . located in the south east portion of fig . [ strings ] , be ori (= hbc 168 ; iras 05345 - 0635 ) is a classical t tauri star with w ( ) @xmath9 10 ( cohen & kuhi 1979 ; strom , margulis & strom 1989a ) . no molecular outflow was detected by levreault ( 1988 ) . the near infrared photometry of strom et al . ( 1989a ) indicates excess emission suggesting the presence of a remnant circumstellar disk . in fig . [ beori ] , our scanned and ccd images clearly show a highly collimated flow originating from be ori . the flow has also been identified by reipurth ( 1999 ; private communication ) . on the scan ( fig . [ beori]a ) , knots b d appear to be linked by a stream of emission which could be interpreted as a jet . be ori itself is surrounded by diffuse emission which extends towards knot a , which is to the south west of the source . all these features are confirmed by our and continuum images ( figs [ beori]b , c ) . all knots appear bright with knot b displaying a combination of emission and continuum emission . designated hh292 , the flow extends along pa = 45with knot a located 1147 to the south west and knots b d located 212 , 473 and 644 to the north east of be ori respectively , making the total flow length 0.4pc . in their survey of l1641 , stanke , mccaughrean & zinnecker ( 1998 ; hereafter smz98 ) identified compact h@xmath6 emission associated with knots a and d ( smz 25 ) , which may represent the terminal working surfaces of the flow where the wind is encountering dense material . it is interesting to note the asymmetry in hhemission with respect to be ori . the lack of optical counterparts to knots b d to the south west of the source suggests be ori has either undergone highly irregular outbursts in the past , or has a one sided jet ( rodrguez & reipurth 1994 ) . assuming a tangential flow velocity of 150 , knots b d have ages approximately 300 , 700 and 1000 yr respectively , suggesting periodic outbursts every 300400 yr whereas knot a has an age of 1700 yr . as the seeing during our observations of be ori was @xmath8 3 , deeper imaging may reveal further hh emission and constrain the ejection history of the source . in fig . [ 1641nopt ] , we present scanned , iiiaf and ivn images of the outlined region in fig . [ strings ] where a cluster of faint red nebulous objects was found by reipurth ( 1985 ) . the region has been mapped in @xmath18co by fukui et al . ( 1986 , 1988 ) who found a bipolar outflow , l1641n , centred on the bright far infrared source iras 053380624 . near infrared imaging of the region by strom et al . ( 1989b ) , chen et al . ( 1993 ) and hodapp & deane ( 1993 ) , revealed a dense cluster of approximately 20 members surrounding the iras source . davis & eislffel ( 1995 ; hereafter de95 ) and smz98 identified a multitude of h@xmath6 ( 2.12@xmath7 m ) emission which outlines a cavity bored out by the co outflow and multiple jet and bow shock features which extend at least 2pc to the south of the embedded cluster . in the following , we present our ccd images of the region shown in fig . [ 1641nopt ] which confirm many of the reipurth nebulosities as bona fide hh objects . scanned images for several of these objects are also presented in parker & phillipps ( 1998b ) . independent ccd imaging of the region has also been presented by r98 . candidate energy sources for these flows are presented based on their location with respect to the optical and near infrared emission ( de95 , smz98 ) . extending to the east of fig . [ 1641nopt ] , the combined image of these two objects ( fig . [ hh301ccd]a ) shows hh301 consists of three bright knots ( a c ) which form an u like structure with several fainter knots ( d f ) trailing to the south west . likewise , hh302 consists of one bright knot ( a ) with a fainter one ( b ) extending to the south west . both objects are brighter in with faint emission . this property is apparent from figs [ 1641nopt]a and [ 1641nopt]b , where hh301/302 are prominent on the iiiaf , but faint in the image . suggest hh301/302 are related based on their elongation towards the l1641n embedded cluster where the presumed driving source is located . a line of emission can be seen to the south which mirrors the position of hh301/302 and coincides with h@xmath6 emission ( smz 17/18 ) . the bright knot hh298a ( r98 ) can also be seen in fig . [ hh301ccd]a . although r98 list hh298 being 70 in extent with an east west orientation , our image shows hh298 extends even further to the east of hh298a with several knots which we label as hh298 d f . this makes the hh298 flow 340 , or 0.76pc in length from knots a to f. it is interesting that together with hh301/302 , hh298 produces a v type structure with the apex pointing back towards the infrared cluster . de95 and smz98 identified a chain of h@xmath6 knots ( i / j and smz 16 a / b respectively ) which extend east from the embedded cluster with a morphology reminiscent of a jet . in fact , hh298a appears directly between smz 16 a and b. as hh298 and hh301/302 contain both optical and near infrared emission , we suggest they are tracing the walls of a cavity outlined by the v type structure . the presence of a jet ( smz 16a ) and counterflow ( hh298a and smz 16b ) suggests we are seeing a single outflow complex . as the jet extends directly between hh298 and hh301/302 , we do not rule out the possibility of 3 separate flows , although we draw a comparison with the outflow source l1551irs5 , where hh28/29 are not located along the jet axis , but close to the walls of a cavity identified by optical , near infrared and co observations ( see davis et al . 1995 and references therein ) . chen et al . ( 1993 ) identified a k band source ( their n23 ) in the direction of de95 i / smz 16b which is not visible in our i band image ( fig . [ hh301ccd]c ) . based on the alignment of optical and near infrared emission , we propose this source as the driving agent for both hh298 and hh301/302 . further spectroscopic studies are needed to clarify its nature . the hh303 flow consists of two groupings of knots aligned along a north south direction . the image in fig . [ hh303ccd]a shows the northern most group ( knots a - f ) outlines a bow shock with a sheath of emission overlaying clumpy emission . several more bright knots ( i k ) extend towards the south . a fainter knot , hh298a ( r98 ) is seen to the south west of knot k. however , fig . 5 of r98 shows hh298a at a different location to that shown in fig . [ hh303ccd]a . therefore , we identify this knot as hh303l in continuation of r98 . r98 suggests hh303l may be associated with hh303 , but deviates too much from the well defined axis and may represent a separate flow . we suggest knots i k and l represent a remnant bow shock with the former and latter representing the eastern and western wings respectively . at first glance , hh303 could be interpreted as a highly collimated flow originating from the variable star v832 ori ( fig . [ hh303ccd]b ) . the optical and near infrared photometry of this source ( source n2 of chen et al . 1993 ) shows a spectral energy distribution which declines rapidly for @xmath19 1@xmath7 m , suggesting a lack of circumstellar material . a comparison of our optical images with the near infrared data of smz98 shows the majority of hh303 displays both optical and h@xmath6 emission , thereby suggesting hh303 is behind v832 ori and unrelated to the star . knots hh 303 b , f and i are coincident with the h@xmath6 knots smz 8a , 8b , and 14p respectively , with the h@xmath6 emission displaying bow shock morphologies which open towards the south in the direction of l1641n . as knots i k lie within the blue lobe of l1641n , it has been suggested the co , near infrared and optical flows derive from a common source ( strom et al . 1989b ; smz98 ; r98 ) . chen et al . ( 1993 ) identified a bright m band source ( their n15 ) @xmath8 8 to the east of the iras position . chen , zhao & ohashi ( 1995 ) detected this source with the vla at 2.0 mm , 7.0 mm and 1.3 cm , while smz98 identified a 10@xmath7 m source coincident with n15 and the vla source . as n15 , the 10@xmath7 m source and the 1.3 cm source represent the same object , we follow r98 and label it as the `` vla source '' which they suggest is the driving source for hh303 and the illuminator of the reflection nebulosity seen to the north east in our i band image ( hd93 ; [ hh303ccd]b ) . however , it is important to mention that the l1641n region is a highly clustered environment where identifying outflow sources requires the highest resolution possible . anglada et al . ( 1998 ) identified two radio continuum sources , vla2 and vla3 , which are 08 and 02 to the west and east respectively from the nominal position of the vla source . further observations of the region reveal a fainter source within 1 of vla2 ( anglada 1998 , private communication ) . the co data of fukui et al . ( 1986 ; 1988 ) clearly indicates the l1641n molecular outflow is more complex than a simple bipolar outflow . higher resolution studies of these sources are needed to determine which source is driving the optical and h@xmath6 emission . in particular , it would be interesting to see if the vla source displays an elongated radio jet with its long axis pointing in the direction of hh303 . in addition to hh303 , r98 suggest the vla source also drives hh61/62 , which are located 468 ( 6.5pc ) to the south of l1641 ( see fig . [ abcd ] ) . if their assumption is correct , the hh61/62/303 flow is 7pc in length , with the northern lobe only 5% the length of the southern lobe . any shocks associated with the northern lobe will be extremely faint due to the lack of molecular material as the flow moves away from l1641 . located to north east of the vla source , the image of hh304 ( fig . [ hh304ccd]a ) shows several compact knots which are bright . knot b is compact with a bow shock structure ( knot a ) extending towards the north east and then curls back to the north west . knots c and d display an opposing bow shock structure , with knots c and d connected by faint emission . the overall morphology of the system suggests the energy source is located between knots a / b and c / d . the i band image ( fig . [ hh304ccd]b ) shows a compact reflection nebulosity with a tail which mimics part of the emission associated with knots a and b. a reddened source ( which we denote as hh304irs ) appears where the reflection emission is most compact . the hh304 complex is also seen in the h@xmath6 mosaic of smz98 , who label it smz 5 . hh304a is seen as a bright bar which extends 6 along an east west direction . at the position of the compact reflection nebulosity , a bright h@xmath6 knot is seen , with a trail of h@xmath6 emission extending from hh304irs towards hh304c . the appearance of the optical and near infrared emission suggests we are seeing two lobes with knots a and c representing the north eastern and south western working surfaces respectively . hh304irs appears midway between these two opposing working surfaces . there are no iras or emission line stars at the location of the reflection nebulosity , which implies a deeply embedded source . the hh305 outflow appears aligned along a north south axis centred on the bright ( v @xmath8 11.3 mag ) star pr ori . with the exception of knots a and f , all objects are bright , with knot b displaying an inverted v type structure only visible in . knot a shows a bow shock structure which opens towards pr ori . it is interesting to note that hh305e represents the brightest nebulosity in the flow . the increased brightness could be attributed to the flow encountering an obstacle of some sort , perhaps in the form of a molecular clump . the dark lane seen in figs [ strings ] , [ 1641nopt ] and [ hh305ccd ] represents a change in the molecular distribution in this part of l1641 . at the position of hh305e , the flow impacts the molecular cloud and then deflects to where we see hh305f . based on their separation from pr ori , r98 suggest knots c / d represent an hhpair located 16 from the source . similarly , knots b / e and a / f represent hhpairs located 65 and 108 from pr ori respectively , making the total flow length 0.54pc . at present , it is unknown if hh305 is being driven by pr ori or a more embedded source behind it ( r98 ) . in a major study of _ einstein _ x ray sources in l1641 , strom et al . ( 1990 ) identified pr ori as a low luminosity ( 13 ) source with a spectral type of k4e@xmath20 and w ( ) = 0.5 . their _ jhklm _ photometry indicates a lack of infrared colour excess normally attributed to a circumstellar disk . based on their data , pr ori appears to be a weak lined t tauri star ( wtts ) . its location with respect to the l1641 molecular cloud shows it lies in a region of low obscuration and in addition to the fact that smz98 did not detect any h@xmath6 emission associated with hh305 rejects the notion of an embedded , more younger source located behind pr ori . if pr ori is the energy source of hh305 , it would present a major discrepancy in star formation theory as wtts are not thought to be associated with circumstellar disks and/or outflow phenomenon . magazzu & martin ( 1994 ) identified what was thought to be a hh flow associated with the wtt , hv tau . woitas & leinert ( 1998 ) suggested the hh object is actually a companion t tauri star with strong forbidden emission lines whose presence originally led magazzu & martin to their conclusions . how do we reconcile the fact that pr ori is a wtts with an outflow ? the answer may lie in table 2 of strom et al . ( 1990 ) , who list pr ori as an optical double . our ccd images also show pr ori as an extended source , in which case it seems more plausible the companion ( pr ori b ) is the driving source of hh305 . clearly , further studies of this hhcomplex are needed . figs [ strings ] and [ flowopt ] show scanned and ivn images of a string of emission line objects ( hh306309 ) extending away from the vla source and up into the main reflection nebulosity of m42 . a large arcuate structure ( hh407 ) can be seen near the bright stars towards the western border . the large rim of emission identified in fig . [ strings ] is seen orientated at pa = 55 and appears to surround all objects in the figure . a comparison of the and ivn images confirms all objects are pure emission line features . in conjunction with the ivn image ( fig . [ flowopt]b ) , our images confirm all as bona fide hh objects . in fig . [ hh306 - 8ccd ] , the image shows hh306 consists of two bright compact knots ( b and f ) with a trail of emission extending to the south . a further knot , hh306 g , lies to the west which may be unrelated , or part of an older fragmented shock . hh307 consists of several bright knots which mark the apexes of large arcs or wings which sweep out and open towards l1641n . r98 suggest hh308 appears as a fragmented bow shock with knots a and b representing the eastern and western wings respectively . located between hh308a and b , we note the presence of a third knot not identified by r98 which we denote here as hh308c . [ hh309ccd ] ) shows a similar structure to hh308 , with knots a and b representing the first fragmented bow shock , knot c the second and knots d / e the third . the reverse bow shock morphology of hh309b can be explained by noting the distribution of emission on the scanned and ccd images . the knot appears to have curled around the background emission which may have been responsible to creating the fragmented appearance of hh309 . in searching for further emission north of hh309 , r98 discovered several bow shock structures , designated hh310 , within the main nebulosity of m42 ( see fig . [ strings ] ) . the objects are brighter in than in , thus discounting the possibility they might be photo ionised rims . we have also imaged these structures and for completeness , present our , and continuum images in fig . [ hh310ccd ] . our frame ( not shown ) does not detect the bow shocks associated with hh310 , thereby suggesting the flow is moving with a velocity less than 100 . our and continuum images ( figs [ hh310ccd]a , b ) identify several bow shock structures to the north west of hh310 which are bright and absent in the continuum frame . assuming for the moment these features are bona fide hh objects , their apparent deviation from the axis defined by hh310 can be explained if the flow is being redirected by an obstacle , possibly the long tongue like feature which extends from the top of the images . an alternative explanation is that they form part of a separate flow , perhaps from the l1641n region . spectroscopic observations of these features are needed to determine if they are hh shocks . to the south of l1641n , smz98 discovered a long chain of bow shocks . designated smz 23 , the chain consists of at least 7 bow shocks ( a g ) which may represent the redshifted counterflow to hh306310 ( this paper , r98 ) . from the @xmath21co data of bally et al . ( 1987 ) , the integrated moment map ( fig . [ 13co ] ) shows evidence of a cavity created by smz 23 . what is interesting about this cavity is its size and orientation with respect to l1641n , hh306310 and the large cavity dubbed by r98 as the `` l1641n chimney '' , which they suggest has been excavated by the repeated passage of bow shocks associated with hh306310 . the location of individual knots associated with smz 23 appears to trace the western wall of the southern cavity , suggesting the flow impacts with the cavity wall which produces the observed emission . we suggest this southern cavity is being excavated by smz 23 as the redshifted flow propagates into and away from l1641n . the @xmath21co velocity structure of the southern cavity is evident from 58 , with the l1641n molecular core and the `` l1641n chimney '' appearing around 8 and 811 respectively . this gives further evidence that the southern cavity and the `` l1641n chimney '' represent expanding red and blueshifted lobes centred on the l1641n region . following similar arguments in r98 , we find the dimensions of this southern cavity to be 5@xmath10 12 in length , giving a total area of @xmath8 1 @xmath10 10@xmath22 @xmath23 . assuming the intensity in the cavity lies within 35 k/ , the total mass excavated by the smz23 flow is @xmath8 3762 . in comparison , r98 find hh306310 has removed @xmath8 190 of gas from l1641 . apart from obvious errors in estimating the @xmath21co intensity and cavity size , we should point out we have not taken into account the possibility the southern cavity may have been formed by the combined action of more than one outflow . smz 23 , hh306309 and hh310 all display large bow shock structures which open towards the l1641n region where the presumed energy source lies . as mentioned for hh303 , the high degree of clustering about the vla source confuses identifying specific energy source(s ) . however the principal components hh306b , hh307a , hh308c and hh309a are located 806 , 1152 , 1331 , 1955 away from the position of the vla source . in addition to hh310a ( 2764 ) , the hh306310 lobe is 6.3pc in length . as the smz 23 flow appears to extend further south from smz23 g ( stanke 1999 ; private communication ) , the geometry of hh306310 and smz 23 about the vla source and vla2/vla3 strongly favours at least one of them as the energy source of the optical and near infrared emission . whichever of these sources is responsible for the observed emission , the combined length of hh306310 and smz23 lobes is 10.5pc . high resolution radio studies will be beneficial for identifying radio jets and their orientation with respect to the optical and near infrared emission . in a search for optical counterparts to hh306310 , our deep iiiaf plate of the southern region of l1641 identifies several features reminiscent of large bow shocks . the iiiaf image of these features is shown in fig . [ abcd ] , where object a appears as a diffuse feature and object b appears as a bright nebulosity with a long curve which extends 16 to the north near object a. at first glance , object b and hh61/62 ( the counterlobe to hh303 ; r98 ) appear to outline the eastern and western wings of a large fragmented bow shock structure . objects c and d appear as large arc like structures which open to the north and are 34 in extent . as c and d are located well away from the main cloud , our line of sight increases which may suggest they are not physically associated with l1641 . we should also note that many of the terminal bow shocks associated with parsec scale hh flows show substantial substructure which is lacking from the iiiaf image . in order to resolve the nature of features c and d , we obtained and images , but due to variable cloud cover , we were not able to classify these objects as bona fide hh objects . deeper images and/or spectra of objects a d are required to determine if they are photo ionised regions or hh objects . to the north east of fig . [ strings ] , a second string of objects extends away from the l1641n cluster . hh403 and hh404 are located well clear of the eastern edge of the l1641 molecular cloud . although seeing at the time of observing was @xmath9 3 , our and ccd images ( not shown ) did allow us to classify these features as genuine hh objects . in fig.[403 - 6opt ] , the scanned and ivn images show hh403 consists of a large number of emission line knots in addition to a curved ( hh403 g ) and amorphous feature ( hh403h ) to the south west . the ccd images of r98 clearly shows hh403 as a highly fragmented object which is very similar in appearance to hh262 ( lpez et al . 1998 ) . a further 9 to the north east , hh404 displays a sickle like structure not too dissimilar from the hh47 jet ( heathcote et al . as these features are bright , r98 raised the question as to whether or not hh403/404 are bow shocks or bright rims . however , based on morphological grounds , they suggest hh403/404 are highly fragmented bow shock structures which point back towards l1641n where the presumed energy source lies . our contrast enhanced scanned image of the region ( fig . [ 403 - 6opt]a ) appears to confirm their suspicion as we see a lack of background emission in the direction of hh403/404 which has probably been removed by the action of the flow as it propagates away from l1641 . the scanned image identifies several large scale bow shocks with hh403 and hh404 at their apexes . r98 do not detect these features on their ccd images . originally thought to be bright rims , comparison of the emission with the @xmath21co data of bally et al . ( 1987 ) , indicates these `` rims '' do not outline the l1641 molecular cloud , or any other well defined @xmath21co ridge . the first bow shock is defined by the arc like object hh403 g and hh404h representing the eastern and western wings respectively . the eastern wing trails 7 to the south before it blends into the background emission . the second bow shock appears as an extended feature similar in appearance to hh403 g . the third bow shock only displays the western wing which extends northward from the second bow to the apex of hh404 , which shows a bright arc with faint emission which combine to form an inverted u type structure . north east of hh404 , a faint object hh405 displays emission extending along pa = 45 . r98 suggest the emission is reminiscent of a jet . a further 6 to the north east , hh406 is a large diffuse object . are hh405 and h406 related to hh403/404 ? the ivn image ( fig . [ 403 - 6opt]b ) shows a reddened source ( denoted hh405irs ) at the position of hh405 . a reflection nebulosity is also seen nearby . the position of the nearest iras source , 05347 - 0545 , is shown in our ivn image . it is a 60 and 100@xmath7 m source only , indicating it is heavily obscured and may be related to hh405 and/or hh406 . based on the location of hh405irs with respect to hh405/406 and the reflection nebulosity , we suggest this source is the driving agent for hh405 and hh406 thereby making the flow length 0.78pc in extent . near infrared polarimetry and imaging will be useful for determining if hh405irs or iras 05347 - 0545 is the illuminator of the reflection emission . located to the far south west of l1641n , r98 noted hh127 mirrors the position of hh404 with l1641n positioned at the centre ( see fig . [ abcd ] ) . although hh127 lies at an angle of 10 from the hh403/404 and l1641n axis , they suggest hh403/404 and hh127 represent the blue and redshifted lobes respectively of a 10.6 parsec scale flow centred on the vla source . given the clustered nature of potential outflow sources about the vla source , proper motion studies of hh127 and hh403/404 are highly desirable to constrain the location of their energy source(s ) . located 283 north west of l1641n and within close proximity to hh306310 , figs [ strings ] and [ flowopt ] identify a large , highly fragmented structure located in the direction of several bright stars . the image [ hh407ccd ] ) confirms it as a bona fide hh object as it emits predominately in . knots a and b display bow shock structures with a streamer ( knots c / d ) extending to the south east . in figs [ strings ] and [ flowopt ] , fainter emission extends a further 6 to the south east of knots c / d . as the streamers of hh407 point towards the l1641n region , it seems probable the energy source lies in that direction . an examination of the h@xmath6 data of smz98 does not reveal any emission extended towards hh407 . after re examining our plate , we noticed the presence of a large loop like structure ( hereafter loop a ) extending out of the reflection nebulosity ngc1999 and in the direction of hh407 . comparison of our scanned , iiiaf and ivn images ( fig . [ 1999opt ] ) indicates loop a is a pure emission line feature . although faintly seen on the iiiaf image , the scanned image clearly distinguishes loop a from background emission . in a recent study of the ngc1999 region , corcoran & ray ( 1995 ; hereafter cr95 ) discovered a second loop ( hereafter loop b ) of emission extending west of the ngc1999 which delineates a poorly collimated outflow associated with hh35 and represents the counterflow to the redshifted molecular co outflow discovered by levreault ( 1988 ) . cr95 suggest the herbig ae / be star v380 ori ( which illuminates ngc1999 ) drives hh35 , loop b and the molecular outflow . the presence of loops a and b suggests the presence of a quadrupole outflow in ngc1999 . using similar arguments as cr95 , we suggest loop a delineates an optical outflow which , in conjunction with hh407 , represents a 6.2pc lobe at pa = -23 with respect to v380 ori . in a search for optical counterparts to hh407 , our deep iiiaf plates do not reveal any clear candidates , although if we assume loop a and hh407 are propagating out and away from l1641 , the southern counterflow may not yet have emerged from the far side of the molecular cloud . stanke ( 1999 ; private communication ) has identified a large h@xmath6 feature to the south of ngc1999 which may represent an embedded counterflow to loop a and hh407 ( see fig . [ 13co ] ) . hh130 is a large bow shock structure located 85 south east of ngc1999 and has been linked to hh1/2 ( ogura & walsh 1992 ) and v380 ori ( reipurth 1998 ) . cr95 suggest the energy source of hh130 is located to the north east of knot h ( see fig . [ 1999opt ] ) . if hh130 and/or the h@xmath6 feature represents the counterflow to loop a and hh407 , the outflow axis would be bent by up to 10 . a similar situation is seen in hh127/403/404 ( r98 ) , hh110/270 ( reipurth , raga & heathcote 1996 ) and hh135/136 ( ogura et al . 1998 ) . proper motion and spectroscopic studies of hh130 , hh407 and the h@xmath6 feature are needed to determine if their motion and radial velocities are directed away from the v380 ori region . is v380 ori the driving source of loop a ? in addition to v380 ori , cr95 found two k band sources , v380 ori b and v380 ori c , within ngc1999 . by means of speckle interferometry , leinert , richichi & hass ( 1997 ) identified v380 ori as a binary consisting of a herbig ae / be ( v380 ori ) and t tauri star . high resolution mm interferometry of ngc1999 will help clarify which source is driving the optical emission associated with loop a. as shown in fig . [ 13co ] , hh306310 , hh407 and the @xmath24shaped filament ( bally et al . 1987 ; johnstone & bally 1999 ) lie within the rim of emission identified in figs [ strings ] and [ flowopt ] . approximated by an ellipse 136 @xmath10 4 ( 3.6 @xmath10 0.54pc ) in size , we suggest the ellipse has formed due to the combined action of the hh306310 and hh407 flows expelling molecular gas from the main cloud core . the uv radiation from the nearby bright stars excites the outer edge of the expanding molecular material which we see as the ellipse . such a large scale movement of molecular gas by parsec scale hh flows has been suggested for hh34 and hh306310 ( bally & devine 1994 ; r98 ) .

we present the results of a photographic and ccd imaging survey for herbig haro ( hh ) objects in the l1630 and l1641 giant molecular clouds in orion . the new hh flows were initially identified from a deep film from the recently commissioned aao / ukst survey of the southern sky . our ccd , , continuum and i band images confirm the presence of a parsec scale hh flow associated with the ori i2 cometary globule and several parsec scale strings of hh emission centred on the l1641n infrared cluster . several smaller outflows display one sided jets .

we present the results of a photographic and ccd imaging survey for herbig haro ( hh ) objects in the l1630 and l1641 giant molecular clouds in orion . the new hh flows were initially identified from a deep film from the recently commissioned aao / ukst survey of the southern sky . our scanned and broad band r images highlight both the improved resolution of the survey and the excellent contrast of the flux with respect to the broad band r. comparative ivn survey images allow us to distinguish between emission and reflection nebulosity . our ccd , , continuum and i band images confirm the presence of a parsec scale hh flow associated with the ori i2 cometary globule and several parsec scale strings of hh emission centred on the l1641n infrared cluster . several smaller outflows display one sided jets . our results indicate that for declinations south of -6 in l1641 , parsec scale flows appear to be the major force in the large scale movement of optical dust and molecular gas . # 1#2#1#2 # 1#2#1#2 # 1#2#3#1#2#3 # 1#2#3 surveys : stars : formation ism : jets and outflows

astro-ph9907371

c

by use of a single aao / ukst film of the orion region , we have identified emission line nebulosities which resemble bow shocks , jets and extensive alignments of arc shaped nebulae indicating possible giant molecular flows . subsequent narrow and broad band ccd imaging has confirmed these features as genuine hh objects tracing outflows ranging in size from a fraction of a parsec to over 6pc in length . in addition to the 3pc wide rim surrounding hh306310 and hh407 , the loop ( loop a ) extending out of the ngc1999 reflection nebulosity have not been identified in previous studies . although these features are faintly visible in our iiiaf images , the excellent contrast of the films with respect to iiiaf and published ccd images of these regions clearly distinguishes these features from background emission , thereby allowing a thorough investigation of how outflows from young stars affect the surrounding interstellar medium . the lack of optical and molecular emission associated with hh403/404 , the presence of the rim and the identification of large @xmath21co cavities associated with hh34 ( bally & devine 1994 ) , hh306310 ( r98 ) and the smz 23 counterflow ( this paper ) suggests that , in the absence of massive star formation , parsec scale flows are the dominating factor in disrupting molecular gas in gmcs . they may also be responsible for the continuation of star formation beyond the current epoch . the creation of large scale cavities seen in @xmath21co maps ( r98 ; this paper ) may produce highly compressed regions which collapse to form a new wave of star formation . in order to test this idea , high resolution sub millimetre observations in conjunction with near infrared h@xmath6 ( 2.12@xmath7 m ) imaging will identify and determine the distribution of newly forming class 0 protostars with respect to the co cavities . although we have suggested candidate energy sources for many of the new hh flows , only a few ( ori i2 , be ori and v510 ori ) can be considered as certain . the identification of at least 4 sources within an arcminute of the vla source warrants subarcsecond co mapping of the region to determine which source is driving the optical and near infrared emission associated with hh306310 , hh403/404 , hh407 and smz 23 . near infrared spectroscopy of proposed outflow sources for hh298/301/302 , hh304 , hh305 and hh405 will be useful in classifying their nature for comparison with other hhenergy sources . to varying degrees , the optical sources be ori and v510 ori exhibit optical variability and multiple ejection events ( hh objects ) . the fact these sources still posses highly collimated , one sided jets well after they have emerged from their parental molecular cloud may provide important insights into jet evolution . in relation to the newly discovered parsec scale flows , high resolution spectroscopy and proper motion studies of individual knots associated with hh61/62/303 , hh306310 , hh127/403/404 , hh407 and features a d to the far south of l1641n will determine velocities , excitation conditions and confirm points of origin . due to the success of the orion film , the carina , cha i / ii , sco ob1 , @xmath25 oph , r cra and cma ob1 star forming regions are to be surveyed in a similar fashion to that presented in this paper . the majority of these cloud complexes lie within 500pc and maximise the detection of faint , large scale flows for comparative studies with the orion region where we hope to address the following questions : * what is the nature of the energy source ? scale flows are associated with class 0 , class i and optically visible t tauri stars . is the parsec scale phenomenon due to inherent properties of the energy source ? * how does the flow remain collimated over such large distances ? does the nature of the surrounding environment have a collimating effect ? * to what extent do parsec scale outflows affect star formation within molecular clouds ? is there any evidence for self regulated star formation ?

our scanned and broad band r images highlight both the improved resolution of the survey and the excellent contrast of the flux with respect to the broad band r. comparative ivn survey images allow us to distinguish between emission and reflection nebulosity . our results indicate that for declinations south of -6 in l1641 , parsec scale flows appear to be the major force in the large scale movement of optical dust and molecular gas .

we present the results of a photographic and ccd imaging survey for herbig haro ( hh ) objects in the l1630 and l1641 giant molecular clouds in orion . the new hh flows were initially identified from a deep film from the recently commissioned aao / ukst survey of the southern sky . our scanned and broad band r images highlight both the improved resolution of the survey and the excellent contrast of the flux with respect to the broad band r. comparative ivn survey images allow us to distinguish between emission and reflection nebulosity . our ccd , , continuum and i band images confirm the presence of a parsec scale hh flow associated with the ori i2 cometary globule and several parsec scale strings of hh emission centred on the l1641n infrared cluster . several smaller outflows display one sided jets . our results indicate that for declinations south of -6 in l1641 , parsec scale flows appear to be the major force in the large scale movement of optical dust and molecular gas . # 1#2#1#2 # 1#2#1#2 # 1#2#3#1#2#3 # 1#2#3 surveys : stars : formation ism : jets and outflows

0805.1335

c

in this paper we have reported the results of a study of a large sample of luminous ( @xmath2 ) lbgs in the redshift interval @xmath1 . by employing a photometric redshift analysis of the available optical+nearir data we have derived improved estimates of the bright end of the uv - selected luminosity function at @xmath9 and @xmath12 . moreover , by combining our new results with those based on deeper , but small area , hst data we have derived improved constraints on the best - fitting schechter function parameters at @xmath9 and @xmath12 . in addition , by studying the angular clustering properties of our sample we have determined that luminous lbgs at @xmath3 typically lie in dark matter halos with masses of @xmath221 . finally , based on the results of a stacking analysis , we have estimated the galaxy stellar mass functions and integrated stellar mass densities at @xmath9 and @xmath12 . our main conclusions can be summarised as follows : 1 . our new determination of the bright end of the high - redshift luminosity function confirms that significant evolution occurs over the redshift interval @xmath3 . based on our results it is clear that the luminosity function evolution can not be described by evolution in normalisation ( @xmath116 ) alone , and that some level of evolution in @xmath158 is also required . a comparison of our new results with those in the literature demonstrates that , within the magnitude range where the two studies overlap , our estimates of the luminosity function at @xmath9 and @xmath12 are in excellent agreement with those derived from ultra - deep hst imaging data by bouwens et al . 3 . by combining our estimate of the bright end of the luminosity function with the corresponding estimates of the faint end by bouwens et al . ( 2007 ) , it is possible to fit the luminosity function at @xmath9 and @xmath12 over a luminosity range spanning a factor of @xmath141 . based on this combined ground - based+hst data - set we find the following best - fitting schechter function parameters : @xmath7 and @xmath8 for the luminosity function at @xmath9 , and @xmath222 and @xmath11 at @xmath12 . 4 . these results are consistent with the corresponding schechter function parameters derived by bouwens et al . ( 2007 ) although , due to the improved statistics at the bright end provided by our wide survey area , the fits to the combined ground - based+hst data - set provide improved constraints on the evolution of @xmath158 in particular . 5 . an analysis of their angular clustering properties demonstrates that luminous @xmath2 lbgs at @xmath3 are strongly clustered , with a correlation length of @xmath176mpc . comparison of these clustering results with theoretical models suggests that these lbgs typically reside in dark matter halos with masses of @xmath223 . an sed fit to a stack of the available optical+nearir data for our sample suggests that luminous lbgs at @xmath3 have typical stellar masses of @xmath210 . combined with the results of the clustering analysis this suggests that the typical ratio of dark matter to stellar mass for luminous lbgs at @xmath3 is @xmath224 . assuming that the mass - to - light ratio derived from the sed fit to the stacked lbg imaging data is representative , we use our best - fitting schechter function parameters for the @xmath9 and @xmath12 luminosity functions to estimate the corresponding stellar mass functions . although clearly subject to large uncertainties , our stellar mass function estimates are consistent with the latest predictions of the semi - analytic galaxy formation models of de lucia & blaizot ( 2007 ) and bower et al . 8 . based on our stellar mass function estimates we calculate that the stellar mass in place at @xmath9 and @xmath12 is @xmath225 mpc@xmath17 and @xmath226 mpc@xmath17 respectively . although uncertain , these independent estimates of the integrated stellar mass density are consistent with the results of studies utilising the ultra - deep spitzer irac data in the goods fields ( stark et al . 2007 ; yan et al . 2006 ) .

we present the results of a study of a large sample of luminous ( ) lyman break galaxies ( lbgs ) in the redshift interval , selected from a contiguous 0.63 square degree area covered by the ukidss ultra deep survey ( uds ) and the subaru xmm - newton survey ( sxds ) . utilising the large area coverage and the excellent available optical+nearir data , we use a photometric redshift analysis to derive a new , robust , measurement of the bright end ( ) of the uv - selected luminosity function at high redshift . a maximum likelihood analysis returns best - fitting schechter function parameters of and for the luminosity function at , and and at . in addition , an analysis of the angular clustering properties of our lbg sample demonstrates that luminous lbgs are strongly clustered (mpc ) , and are consistent with the occupation of dark matter halos with masses of .

we present the results of a study of a large sample of luminous ( ) lyman break galaxies ( lbgs ) in the redshift interval , selected from a contiguous 0.63 square degree area covered by the ukidss ultra deep survey ( uds ) and the subaru xmm - newton survey ( sxds ) . utilising the large area coverage and the excellent available optical+nearir data , we use a photometric redshift analysis to derive a new , robust , measurement of the bright end ( ) of the uv - selected luminosity function at high redshift . when combined with literature studies of the fainter lbg population , our new sample provides improved constraints on the luminosity function of redshift lbgs over the luminosity range 0.1l ll . a maximum likelihood analysis returns best - fitting schechter function parameters of and for the luminosity function at , and and at . in addition , an analysis of the angular clustering properties of our lbg sample demonstrates that luminous lbgs are strongly clustered (mpc ) , and are consistent with the occupation of dark matter halos with masses of . moreover , by stacking the available multi - wavelength imaging data for the high - redshift lbgs it is possible to place useful constraints on their typical stellar mass . the results of this analysis suggest that luminous lbgs at have an average stellar mass of , consistent with the results of the clustering analysis assuming plausible values for the ratio of stellar to dark matter . finally , by combining our luminosity function results with those of the stacking analysis we derive estimates of mpc and mpc for the stellar mass density at and respectively . # 1to 0pt#1 # 1 # 1 to size # 1 to size = cmr10 scaled2 = cmbx10 scaled2 = cmti10 scaled2 ps . 2 = 6truein galaxies : high - redshift - galaxies : evolution - galaxies : formation

astro-ph0602091

i

cyg x-1 is one of the brightest high - energy sources in the sky , with an average 1 - 200 kev energy flux of @xmath4 ergs @xmath5s@xmath6 . its optical companion is an o9.7 iab supergiant hde 226868 . estimates of the mass , m , of the x - ray star , @xmath7 [ e.g. , @xcite ] strongly suggest the presence of a black hole . observed spectral and temporal x - ray characteristics are extensively studied based on the large amount of data collected in the _ rxte _ archive ( see 2 for the data description ) . our analysis includes @xmath0 2.2 ms of rossi x - ray time explorer ( _ rxte _ ) archival data from cyg x-1 to study the spectral and timing properties of this classical bhc source . one of the basic questions addressed in many observational and theoretical studies concerning relativistic compact objects is how to observationally distinguish between a neutron star ( ns ) and a black hole ( bh ) . cyg x-1 , being extensively studied , has often been used as the prototypical example of a bh . the different patterns , for example correlations between spectral and timing characteristics of bh and ns sources , has been proposed as a criteria for determination of the nature of the compact object . recently belloni ( 2005 ) and @xcite published a concise review of the observational features of the spectral states in bh sources where they also point out a link between timing and spectral properties of x - ray radiation and plasma ejection leading to radio jets . @xcite , hereafter tf04 , and @xcite , hereafter tsh05 , present theoretical and observational arguments how to distinguish between bh and ns binaries . tf04 present observational evidence that in bhs two distinct phases occur : one of them , the steep power - law phase ( so `` called '' high / soft state ) , is the signature of a bh . in the soft state of bh the spectral index - quasiperiodic oscillation ( qpo ) frequency correlation shows a flattening , or `` saturation '' of the photon index @xmath8 at high values of the low frequency @xmath9 . this saturation effect was identified as a bh signature . tsh05 demonstrate that this saturation is not present in at least one ns source . they show that for 4u 1728 - 34 the index @xmath10 increases monotonically with @xmath9 . we show here that cyg x-1 is a perfect example of a bh source as the suggested bh index - qpo frequency correlation is observed with clear features of the saturation at high and low frequencies . long - term monitoring of cyg x-1 has revealed two distinct spectral states and transitions between them [ see a review of cyg x-1 early observations in @xcite ] . simultaneous , low- and high energy x - ray observations during interstate transitions have been obtained by several groups in 1996 [ see references in @xcite and @xcite ] . in the low / hard state , the power - law portion of the spectrum is relatively flat with a photon index @xmath10 of about 1.5 . they found that a majority of the time cyg x-1 stayed in the low / hard with an occasional transition ( during their observations , duty cycle of this state was about 90 % ) to the soft state where the power - law spectrum became significantly steeper ( with @xmath11 ) . also , one or two times per year cyg x-1 exhibited so called `` failed state transitons '' , when it started to transition but did not reach a soft state , stopping at some intermediate state and their falling back . thus one can claim that the source was predominantly in a hard state in 90s . however wilms et al . ( 2005 ) have recently shown that since 2000 the source spent @xmath12 of the time in the intermediate and the soft state . we came to the same conclusion as a result of our analysis of the source spectral transition ( see more discussion of this phenomenon in 4 , the last paragraph ) . as @xcite pointed out there is strong evidence that the observed qpo characteristics are related to spectral properties : the qpo amplitude increases as the energy spectrum becomes harder . they also discovered qpo low - frequencies varying in the range of 4 - 10 hz during the spectral transition . in fact , using these observations di matteo & psaltis ( 1999 ) , hereafter dp99 , found that the photon index can be correlated with the qpo frequency . one can see a few points of this correlation in the frequency range from 1 to 10 hz in their figure 1 . this behavior was later confirmed by @xcite , hereafter p03 , using observations of the cyg x-1 spectral transition in 2000 - 2001 . it is worth noting that dp99 also suggested that the index - qpo frequency correlation can be a common phenomenon for black hole sources . in this paper we present a detailed study of spectral transitions in cyg x-1 and demonstrate how the energy spectra are related to the power density spectra ( pdss ) , in particular the qpo features . we find that the index - qpo correlation is similar to previous findings for bh sources , e.g. dp99 , @xcite and tf04 , where the qpo frequency - index correlation is presented for large samples of bh sources . in pdss observed by _ rxte _ for cyg x-1 , we show that these qpo low frequencies tightly correlate with the break frequency @xmath13 . @xcite presented a model for the radial oscillations and diffusion in the transition layer ( tl ) surrounding the bh and ns . using dimensional analysis , they identified the corresponding radial oscillation and diffusion frequencies in the tl with the low - lorentzian @xmath2 and break frequencies @xmath13 for 4u 1728 - 34 . they predicted values for @xmath13 related to the diffusion in the transition layer , that are consistent with the observed @xmath13 . both the keplerian and radial oscillations , along with diffusion in the transition layer , are controlled by the same parameter : the reynolds number @xmath14 ( inverse of @xmath15-viscosity parameter ) , which in turn is related to the accretion rate [ see also @xcite , hereafter tlm98 ] . it is worth noting that the identification of the break frequency as a diffusion effect ( the inverse of time of the diffusion propagation in the bounded configuration ) was later corroborated by both @xcite and @xcite . particularly , wood et al . demonstrated that the black hole candidate ( bhc ) xte 1118 + 480 x - ray light curves with fast rise / exponential decay profile are a consequence of the diffusion matter propagation in the disk . on the other hand , gilfanov & arefiev ( 2005 ) studied x - ray variability of persistent lmxbs in the @xmath16 hz frequency range aiming to detect pds features associated with the diffusion time scale of the accretion disk @xmath17 . as this is the longest intrinsic time scale of the disk , the power spectrum is expected to be independent of the frequency below @xmath18 . they found that the break frequency correlates very well with the binary orbital frequency in a broad range of binary periods from @xmath19 min to 33.5 days , in accord with theoretical expectations for the diffusion time scale of the disk . @xcite found while the low - energy x - ray ( 1.3 - 12 kev ) and high - energy x - ray ( 20 - 200 kev ) fluxes strongly anticorrelate during the spectral transition , the bolometric luminosity in the soft states may only be 50%-70% greater than the hard state luminosity . on the other hand , @xcite found that the increase of the bolometric flux in the high / soft state with respect to that in the low / hard state is about s factor of @xmath20 . in this paper we further explore this issue of the bolometric luminosity using the data collected from the pca and hexte detectors of _ rxte_. in fact , we confirm zhang s et al . finding that the bolometric luminosity slightly increases when cyg x-1 undergoes transition from the low / hard to the soft states . we also comment on the issue of how the wind in cyg x-1 affects the bolometric luminosity . @xcite and @xcite argue that the x - ray source in cyg x-1 is powered mainly by accretion from the strong stellar wind of the supergiant star . cyg x-1 probably represents a situation intermediate between pure , spherical wind accretion and accretion by roche lobe overflow . as @xcite pointed out the density of the wind determines the size of x - ray ionization zone surrounding the black hole . this in turn controls the acceleration of the wind in the direction of the black hole . during the low / hard state , the strong wind is fast and accretion rate is relatively low , while during the soft state , the weaker , ionized wind attains only a moderate velocity and the accretion rate increases . it is evident that the thomson optical depth of the wind increases in spectral transition because of decrease of the wind velocity ( even if outflow mass rate is constant through the state transition ) . we further investigate the effects of the wind in cyg x-1 in terms of power and energy spectra , bolometric luminosities and the strength of k@xmath3 iron line emission . the iron line observed in cyg x-1 is the strongest among the galactic black holes . @xcite discovered the broad fe k@xmath3 line , with equivalent width @xmath21 ev and fwhm=1.2 kev in an _ exosat _ spectrum of cyg x-1 . because of these features are broad one should be concerned that the profiles are artifacts of inadequate continuum models or instrumental effects . miller et al . ( 2002 ) argue that an fe k@xmath3 line is required to obtain statistically acceptable fits to spectra observed from cyg x-1 with a number of instruments , for a variety of continuum models and source luminosities [ see @xcite , and @xcite for _ asca _ results , and see @xcite and @xcite for _ bepposax _ results ] . it is important to emphasize that most of the observations indicate that the relatively strong broad fe k@xmath3 line emission which ew is within a range of 100 - 300 ev while miller et al . claim their best - fit model for chandra spectrum includes a broad line ( @xmath22 kev , fwhm@xmath23 kev , @xmath24 ev ) component along with a narrow gaussian emission line ( @xmath25 kev , fwhm@xmath26 ev , @xmath27 ev ) component . it is clear that the inferred values of line energy e , fwhm and ew are affected by the energy resolution of a given instrument and by the continuum model applied [ see e.g. @xcite ] . recently @xcite revealed a strong and broad fe k@xmath3 line in another black hole source , grs 1915 + 105 ( @xmath28 ev ) . they suggest that there should be a link between ews and qpo frequencies in bh sources . here we show that indeed there are correlations between the strength of the iron line , qpo frequency and the spectral index . the observational signature of the mass accretion rate @xmath29 is the qpo low frequency as it has been shown for bh sources by tf04 . the qpo frequency is related not only to @xmath29 but also to the size of the comptonizing region , @xmath30 , i.e. @xmath31 . the behavior of @xmath32 with respect to spectral index @xmath10 connects the characteristics of the comptonization and spectral state with @xmath29 . this is graphically represented for bhs in the observations of @xcite . we similarly employ this type of analysis to compare cyg x-1 spectral states with other bhs to show their qualitative differences . in 2 we present the details of the our spectral and timing data analysis of archival rxte data from the bh source cyg x-1 . in 3 we present and discuss the results of the data analysis and we compare them to that presented by tf04 for other bh sources . in 3 we also offer an explanation various correlations found in cyg x-1 . discussion and conclusions follow in 4 .

we present timing and spectral analysis of 2.2 ms of rossi x - ray time explorer ( _ rxte _ ) archival data from cyg x-1 . using a generic comptonization model we find a strong correlation between the 0.1 - 20 hz frequencies of quasiperiodic oscillations ( qpos ) and the spectral index . presence of two spectral phases ( states ) are clearly seen in the data when the spectral indices saturate at low and high values of qpo frequencies . this saturation effect was discovered earlier in a number of black hole candidate ( bhc ) sources and now we strongly confirm this phenomenon in cyg x-1 . in the soft state this index - qpo frequency correlation shows a saturation of the photon index at high values of the low frequency . we also present the spectral state ( power - law index ) evolution for eight years of cyg x-1 observations by _

we present timing and spectral analysis of 2.2 ms of rossi x - ray time explorer ( _ rxte _ ) archival data from cyg x-1 . using a generic comptonization model we reveal that the spectrum of cyg x-1 consists of three components : a thermal seed photon spectrum , a comptonized part of the seed photon spectrum and the iron line . we find a strong correlation between the 0.1 - 20 hz frequencies of quasiperiodic oscillations ( qpos ) and the spectral index . presence of two spectral phases ( states ) are clearly seen in the data when the spectral indices saturate at low and high values of qpo frequencies . this saturation effect was discovered earlier in a number of black hole candidate ( bhc ) sources and now we strongly confirm this phenomenon in cyg x-1 . in the soft state this index - qpo frequency correlation shows a saturation of the photon index at high values of the low frequency . the saturation level of is the lowest value found yet in bhcs . the bolometric luminosity does not show clear correlation with the index . we also show that fe k emission line strength ( equivalent width , ew ) correlates with the qpo frequency . the ew increases from 200 ev in the low / hard state to 1.5 kev in the high / soft state . the observational correlations revealed compel us to propose a scenario for the spectral transition and iron line formation which occur in bhc sources . we also present the spectral state ( power - law index ) evolution for eight years of cyg x-1 observations by _

astro-ph0602091

r

the evolution of spectral properties of the source during the transition from the low / hard to the soft states is shown on figure [ spevol ] and in table [ statestab ] . the temperature profile of the thermal ( blackbody ) component is plotted versus the index @xmath10 in figure [ kt ] . this temperature is presumably related to the disk . it changes only slightly in the narrow range of 0.5 -0.6 kev and is nearly independent of the spectral state . when the source is in the low / hard state the emerging radiation spectrum is presumably formed as a result of comptonization of soft photons generated in the disk . we present a @xmath49- diagram for the low / hard state in upper left hand panel of figure [ spevol ] ( @xmath50 is the energy flux ) . as a source progresses to higher luminosity states the spectrum becomes softer , the power - law part of the spectrum becomes steeper and the contribution of the blackbody ( thermal ) component increases . the strength of the iron line also increases ( see the right upper panel in figure [ spevol ] ) . one can explain this evolution of the spectrum by an increasingly efficient deposition of the gravitational energy in the disk which becomes stronger towards the soft states ( see e.g. * ? ? ? * ; * ? ? ? the luminosity reaches the highest level in the soft state when the spectral index @xmath10 is about 2 . the power - law plateau is clearly seen in @xmath49- diagram presented in the lower left hand panel of figure [ spevol ] . then , as the spectral index increases we observe a slight decrease in flux . we identify this phase as a very soft state ( the so called thermal dominated state " ) , in addition to the canonical low / hard , intermediate and soft states . the energy spectrum is dominated by thermal component ( more than 70% of total flux ) and the maximum observed spectral index is @xmath51 . it is important to emphasize that , typically , the high / soft state in the bh sources is observed when an extended power - law component has index @xmath52 [ see e.g. @xcite , @xcite , hereafter brt99 , tf04 ] . this relatively low index for cyg x-1 soft state can be explained by a higher temperature of the converging flow than that for the high / soft state of other bh sources ( see * ? ? ? * hereafter lt99 , and also tf04 ) . the main reason for this may be the fact that in the soft state of cyg x-1 , the energy release in the disk and in the compton cloud are comparable while in the typical lmxb bh sources , like grs 1915 + 105 , xte j1550 - 564 , gro 1655 - 40 , in the high / soft state the energy release in the disk is much greater . when spectral index progresses to values higher than @xmath53 the luminosity decreases ( see the lower right hand panel of figure [ spevol ] ) . it is worth noting that we use a terminology for the spectral states in cyg x-1 based on our physical scenario of the spectral evolution there ( see more of the details in the discussion section ) . in our classification the difference between soft and very soft states corresponds to the difference in the spectral indices . in soft state when the saturation of the spectral index @xmath10 vs qpo frequency @xmath9 occurs , @xmath10 is about 2 ( see 3.4 ) . whereas in the very soft state the spectra become softer and @xmath10 increases to the values of 2.7 . no qpo frequencies are observed in this state . in the scheme of mcclintock and remillard ( 2004 ) ( and every other `` high '' or `` very high state '' bhc sources ) this classification can look different . one should be careful in applying the definition of spectral states ( particularly soft states ) for some particular source . the next important question is how this spectral evolution is related to the timing characteristics of the source . in our study of the power density spectrum ( pds ) , we reveal that the pds features , break frequency @xmath13 , and lorentzian low - frequency @xmath9 and q - value of the qpo frequency evolve and increase while the source progresses toward the soft state . but the qpo frequencies are completely washed out in the very soft state . @xcite , hereafter tcw02 , predicted that when the source is embedded in the optically thick medium the qpo features must be absent in the pds of the source because of photon scattering . when the radiation from the central source passes through the surrounding cloud of optical depth @xmath54 and of radius @xmath30 the direct ( unscattered ) and scatterred fractions of the radiation are @xmath55 and [ @xmath56 respectively . consequently the rms amplitude of the direct component decreases exponentially with @xmath54 . tcw02 show that the rms amplitude of the scattered component @xmath57 for a given rotational frequency @xmath58 decreases as @xmath59 where @xmath60 ^ 4 + ( 3r\tau_0\omega/4c)^2\}^{1/2}$ ] . as seen from equation ( [ bomega ] ) , the qpo amplitude of the radiation scatterred in the wind ( cloud ) decreases very rapidly with @xmath54 and with @xmath61 ( @xmath62 ) , namely @xmath63 a radius r of @xmath64 cm was chosen as a typical radius of the wind inferred from the observations [ @xcite ] and theoretically inferred using luminosity and spectrum as observable characteristics of the source [ @xcite ] . thus we can conclude that the variability of the scatterred part of radiation is completely washed out in the wind of radius of order @xmath64 cm even for @xmath65 . the variability of the direct ( unscattered ) component is preserved but its rms amplitude decreases as @xmath55 with @xmath54 . the power spectrum analysis of cyg x-1 data confirms this expectation ( see pottschmidt et 2003 ; axelsson , borgonovo & larsson 2005 and our results in this paper ) . the power spectrum in the very soft state is featureless ( see fig . [ power ] ) . the emission of the central source is presumably obscured by the optically thick wind and consequently all photons emanating from the central source are scattered . the direct component of the central source radiation that carries information about the variability is suppressed by scattering . @xcite argue that there is a particular state of cyg x-1 when the wind velocity is very low and thus one can expect high accumulation material in the wind and high optical depth of the wind . the wind downscattering of the photons emanating from the inner compton cloud leads to the softening of spectrum @xcite and consequently to a decrease in x - ray luminosity of the source . the softening of the spectrum can also be a result of effective cooling the compton cloud by the disk soft photons . if the power law component of the soft state is formed in the converging flow , then the high indices are a result of the low flow temperature ( lt99 ) . the index increases and saturates to the critical value about 2.8 with the mass accretion rate for the low temperatures of the flow ( see lt99 and titarchuk & zannias 1998 , hereafter tz98 ) . to calculate the power spectrum of the central source emission affected by scattering one should present the quantitative model of the resulting pulse affected by scattering @xmath66 which can be written as follows : @xmath67 where @xmath68 is the input pulse of the central source oscillations and @xmath69 is the response pulse of the scattering medium . the power spectrum of @xmath66 is a product of the power spectrum of @xmath68 and @xmath69 , i.e. @xmath70 where @xmath71 @xmath72 @xmath73 are fourier transforms of @xmath74 respectively . the time response of the innermost part of the source @xmath68 can be considered in terms of diffusion propagation of perturbation in the disk transition layer ( tl ) . any local perturbation in tl ( bounded medium ) would propagate diffusively outward over time scale ( see tl99 ) @xmath75 where @xmath76 is the characteristic thickness of the tl , @xmath77 is the mean free perturbation path related to the turbulent mhd viscosity @xmath78 , the matter density @xmath79 , the number density @xmath80 and the perturbation interaction cross - section @xmath81 in the tl and @xmath82 . even though the specific mechanism providing this viscosity needs to be understood , this time scale @xmath83 apparently `` controls '' the diffusion supply of the matter into the innermost region of the accretion disk ( tl ) . the response function @xmath68 is a solution the time - dependent problem for perturbation diffusion that mathematically is formulated as an initial value problem for the diffusion equation in the bounded medium ( see more details of the diffusion theory in st80 , st85 , t94 ) . this solution is a linear combination @xmath84 where @xmath85 is a free path crossing time , @xmath86 is kth eigen diffusion time , @xmath87 , @xmath88 is expansion coefficient of the source perturbation function @xmath89 @xmath90 that is related to eigenvalues @xmath91 and eigen functions @xmath92 of the appropriate space diffusion operator and @xmath93 is the operator weight function . if @xmath94 then the response function as a solution of the diffusion problem can be presented by a single exponent , namely @xmath95 because in this case @xmath96 and @xmath97 , for @xmath98 , where @xmath99 ( st80 , st85 , t94 ) . the scattering response function @xmath69 is a solution of the diffusion problem for the photon scattering in the extended envelope ( wind ) that surrounds the central source . the formula for the photon diffusion time @xmath100 is very similar to formula ( [ cstime ] ) , i.e. @xmath101 where @xmath102 is the envelope thickness and the thomson optical depth of the envelope @xmath103 . when @xmath104 ( similarly that for the perturbation diffusion ) the scattering diffusion function @xmath69 can be presented by the exponent @xmath105 it is worth noting that @xmath106 , because @xmath107 by definition of @xmath108 and @xmath109 . for these particular response functions ( see eqs . [ xtdiff ] , [ gtdiff0 ] ) the power spectra are @xmath110 @xmath111 and @xmath112 because @xmath106 we have the following asymptotics for the power spectrum @xmath113 as a function of @xmath114 ) @xmath115 one can clear see the change of the power - law index of the @xmath116power diagram from @xmath117 to @xmath118 about 0.08 , 0.5 , 3 hz in the low / hard , intermediate and the soft states respectively . thus one conclude that the perturbation diffusion times in the tl ( compton cloud ) @xmath119 hz ) are about @xmath120 s in these states . the change of the power - law index of the diagram from ( 1 ) to ( -1 ) [ that corresponds to 0 -(-2 ) changes of that in the power spectrum ( eqs . [ pwasym1 ] , [ pwasym2 ] ) ] takes place in the low - frequency parts of the diagrams for the low / hard , intermediate and soft states ( black , blue , red respectively ) . the power at high frequencies decays very fast and the corresponding power - law index of pds is about 4 ( see eq . [ pwasym3 ] ) . however in the @xmath116power diagram for the very soft state the index changes from 0 to ( -1 ) at low - frequency ( about 0.2 hz ) but this change is not described by aforementioned formulas ( [ power0 ] , see also [ pwasym1 ] , [ pwasym2 ] ) . we argue this particular power - law index transition occurs in the source when the optical depth of the wind @xmath121 . in order to demonstrate this effect one must calculate the power spectrum of the scattering response function @xmath69 for @xmath121 . the derivation of these formulas are out of scope of the paper and we shall present these results elsewhere . it is worth commenting that we have already shown here , the resulting power spectrum is a product of two power spectra related to the disk pds and another one to compton cloud ( scattering ) pds ( see eq . [ pwsp ] ) . in the general case , each of these spectra is a power spectrum of the series of eigen exponential shots [ see for example , formula [ xtdiff ] for @xmath68 ] . for frequencies much less than the characteristic scattering frequency , @xmath123 the resulting spectrum is represented by a power - law red noise component . in our simple treatment of this problem considered here and applicable to the hard and intermediate states only ( see eq . [ power0 ] ) the low - frequency power - law index of pds is zero . in fact , the index and power - law cuttoff frequency increases with mass accretion rate when the source undergoes transition to a soft state . we shall provide all details of this correlation in a future publication . another observational appearance of the wind is the strong broad feature of k@xmath3 line in the spectrum that is present in all spectral states of cyg x-1 ( see fig . [ spevol ] ) . in figure [ line_index ] ( upper panel ) we demonstrate how equivalent width ew of the k@xmath3 line increases with the photon index @xmath10 from about 150 ev in the low / hard state to about 1.3 kev in the high / soft and very soft states . one can see signs of saturation of the ew at about 1.3 kev for indices above 2.1 when no qpo is present in the power spectrum . wilms et al . ( 2005 ) have also found that one needs a strong k@xmath3 line for fitting data with a comptonization model ( comptt ) . the strength of the line increases almost linearly with a accretion disk flux until it satures at the values of @xmath124 kev . the x - ray photons presumably originated in the innermost part of source , in an area less than 40 schwarzschild radii , illuminate the wind . in this case the wind gas is heated by compton scattering and photoionizations from the central object . it is cooled by radiation , ionization , and adiabatic expansion losses ( lat04 ) . the photons above the k - edge energy are absorbed and ionize iron atoms that leads to the formation of the strong k@xmath3 line . lat04 calculated ionization , temperature structure and the equivalent widths of fe k@xmath3 line formed in the wind . for the wide set of parameters of the wind ( velocity , the thomson optical depth @xmath125 ) and the incident comptonization spectrum ( the index and the compton cloud electron temperature ) they established that ew of the line should be about 1 kev and less for the line to be observed . lat04 also predicted that for this case the inner radius of the wind should be situated at @xmath126 schwarzschild radii away from the central object . in the framework of the wind model we can inferred the optical depth of the outer shield ( wind ) as a function of the index using the ew of k@xmath3 line [ see @xcite , ct95 ] : @xmath127\}de . \label{ew_tau}\ ] ] where @xmath128 is the fluorescence yield , @xmath129 is the k shell ionization threshold energy , @xmath130 and @xmath131 are the abundances of elements ( in units of the cosmic abundances ) with a charge @xmath132 and the iron abundance , respectively . this integral can easy be calculated using the following formula @xmath133^m}{(3m+\alpha-1)m!}\left(\frac{7.8~{\rm kev } } { e_{th}}\right)^{3m-1}. \label{ew_tau_form}\ ] ] we apply the value of @xmath134 kev [ see @xcite ] , and @xmath135 [ see @xcite ] . in figure [ line_index ] ( lower panel ) we present the inferred dependence of @xmath136 on the photon index . to obtain a description of the x - ray photon spectrum of cyg x-1 many authors ( see e.g. gilfanov , churazov & revnivtsev 1999 , hereafter gcr99 ; p03 ) used an empirical model in which each source spectrum is a sum of power law spectrum with photon index @xmath10 and a multi - temperature disk blackbody ( makishima et al . 1986 ) . to this continuum , a reflection spectrum after mz95 was added . gcr99 emphasized that this empirical model is obviously oversimplified and therefore the best - fit parameter values do not necessarily represent physically meaningful quantities . particular problems arise with the values of the reflection factor @xmath137 and the equivalent width of the iron line . the best - fit values of @xmath137 for the soft state exceed the unity considerably @xmath138 , which is physically meaningless in the geometry of the reflection . in fact , lapidus , sunyaev & titarchuk ( 1985 ) , showed that the maximum reflection factor for geometrically thin infinite disk illuminated by isotropic radiation from the central object is 0.25 . the values of the ew of k@xmath3 inferred by gcr99 vary from 80 to 300 ev . these ews are related to the line component included in the spectrum in addition to the refelection component . because the reflection model includes its own iron line component ( mz95 ) thus the actual strength of the line is much higher in cyg x-1 than that presented in gcr99 . one can determine that the total iron line strength strongly increases with photon index because of the power of the so called `` reflection component '' r , which also strongly increases with the index ( see figs 5 , 8 in cgr99 ) . in this sense our inferred strong lines in the soft states of cyg x-1 agree with those in gcr99 . in figure [ ind_qpo ] we present the correlation of photon index @xmath10 versus low qpo frequency @xmath9 ( orange points in the upper panel ) and the correlation of @xmath10 versus break frequency @xmath13 ( the lower panel ) observed in cyg x-1 . we compare the index - qpo correlation with those observed in grs 1915 + 105 , xte j1550 - 564 . one notices similar properties for all of these sources : i. when qpo is detected the photon index does not go above 3 , ii . the index saturates . at low and high values of the qpo frequencies . in cyg x-1 the saturation level of the index for high values of low qpo frequency is remarkably lower than for the other two sources . tf04 argues that the index saturation level is determined by the temperature of the converging flow where the soft ( disk ) photons are upscattered by electrons to the energy of falling electrons ( lt99 ) . in principle , one can evaluate the mass of the central bh using the index - qpo relation because qpo frequencies are inversely proportional mass ( tf04 ) . the simple slide of the index - qpo correlation for xte j1550 - 564 ( pink line ) over the frequency axis gives us the index - qpo correlation for grs 1915 + 105 ( blue line ) . the shifting factor is 10/12 which gives the relative bh mass in xte j1550 - 564 with respect to that in grs 1915 + 105 . but one caveat should be taken into account : this sliding method works if the index - qpo relations are self - similar with respect to each other as occurs for grs 1915 + 105 and xte j1550 - 564 . in figure [ flux - index ] we show how the 1 - 30 kev flux ( black crosses ) varies during the spectral transition from the low / hard state ( l / h ) to very soft ( vs ) state . we use joint pca / hexte spectral fits for bolometric corrections for high energies . we extracted hexte spectra from cluster a and cluster b using the same screening criteria that we obtained for pca spectra . to fit pca / hexte data we apply the model obtained for pca multiplied by high energy cutoff ( _ highecut _ ) component to account for high energy turnover in the hard tail of the x - ray spectrum . the flux is then calculated by integrating the best - fit model spectrum over the energy interval from 1 kev to 300 kev . absolute normalization of hexte data for both clusters were allowed to change free with respect to pca normalization . the resulting fits show the hexte normalization consistently less than the normalization for pca by 15 - 20% as expected . resulting values of bolometric flux are shown on figure [ flux - index ] ( red circles ) . we confirmed zhang s et al . ( 1997 ) claims that the bolometric flux remains almost unchanged ( within 50% , almost ) during l / h to vs transition . this phenomenon can be explained as a combined effect of the mass accretion rate increase and the comptonization enhancement decrease when the system undergoes the spectral transition . in the low / hard state the relative small energy release ( low mass accretion rate ) in the disk is compensated by high comptonization efficiency in the corona while in the very soft ( thermal dominated ) state the situation is opposite . sunyaev & titarchuk ( 1980 ) , hereafter st80 , and sunyaev & titarchuk ( 1985 ) , hereafter st85 , derive the asymptotic form of the comptonization enhancement factor @xmath139 for both regimes of the energy spectral index ( @xmath140 and @xmath141 ) . chakrabarti & titarchuk ( 1995 ) , hereafter ct95 , provides the general formula for @xmath139 ( ct95 , formula 14 ) which combines these two asymptotic . in order to infer the bolometric flux dependence @xmath142 on the photon index using the observable thermal ( disk ) flux @xmath143 one should multiply @xmath143 by @xmath144 $ ] and apply formula ( 14 ) in ct95 for @xmath139 , namely @xmath145 , \label{flux_bol}\ ] ] where @xmath146 , @xmath40 is a color temperature of disk radiation ( see fig [ kt ] ) and @xmath147 is electron temperature of compton cloud . the enhancement factor @xmath139 depends on @xmath147 only for @xmath140 ( @xmath148 ) ( see formula 14 in ct95 ) . in order to infer @xmath147 we apply use the same pca / hexte data . to calculate the electron temperature @xmath147 we use the _ highecut _ parameter , @xmath149 and well - known relation between the electron temperature and the high energy cutoff of the comptonization spectrum , namely @xmath150 ( see e.g. st80 and t94 ) . we present the results of calulations of @xmath151 as a function of @xmath152 for different values of @xmath153 ( see fig . [ ecomp ] ) . in figure [ flux - index ] we demonstrate a dependence of @xmath142 on the photon index @xmath152 ( blue triangles ) . the theoretically predicted and observed flux values are in good agreement along . thus _ the inferred luminosty - index relation supports the idea that the variation of luminosity with index is due to the combined effect of the disk mass accretion rate and comptonization of the disk photons in the corona_. the soft photon radiation is completely comptonized in the low / hard state while the relative contribution of the comptonized radiation decreases toward the very soft ( thermal dominated ) state . in figure [ comp_ratio ] we present the observed correlation between the ratio of the comptonized flux to the bolometric flux and the index . the comptonized spectrum is a convolution of the soft photon spectrum with the upscattering comptonization green s function . this component of the observable spectrum and consequently the related flux can be obtained using the bmc model . the inferred comptonized fraction of the spectrum helps us to reveal the relative size of the corona ( compton cloud ) with respect to the disk emission region . one can see that in the soft states the coronal region becomes more compact . this effect is also confirmed by the observed index - qpo correlations ( see fig . [ ind_qpo ] ) . the qpo frequencies increases with the index as a result of the mass accretion rate increase . in fact , the coronal region is pushed close to bh when mass accretion rate goes up ( see tlm98 and tf04 ) . in the soft states ( when the compton cloud is relatively cold ) the converging flow site ( @xmath154 ) is only the place where the soft ( disk ) photons get scattered due to the dynamical comptonization . in figure [ br_lowfr ] we present the observed correlation between the break frequency @xmath13 and the low frequency @xmath9 . we fit this correlation by the broken power law of the form @xmath155 the best - fit parameters : the normalization @xmath156 , the `` low''-frequency index @xmath157 and the `` high '' frequency index @xmath158 and the `` boundary '' index @xmath159 hz . titarchuk , osherovich & kuznetsov ( 1999 ) found that the `` high '' frequency index @xmath160 is a canonical index of break - low frequency correlation for a quite a few bh and ns sources . in fact , titarchuk & osherovich ( 1999 ) identified using dimensional analysis the corresponding radial oscillation and diffusion frequencies in the transition layer ( tl ) with the low - lorentzian @xmath2 and break frequencies @xmath13 for 4u 1728 - 34 . they predicted values for @xmath13 related to the diffusion in the transition layer , that are consistent with the observed @xmath13 . to99 argue that @xmath2 is the inverse of the oscillation time of the tl radial mode , @xmath161 and @xmath162 is the inverse of the diffusion time of the perturbation propagation in the tl @xmath163 where @xmath109 is the tl radial size ( see definition of @xmath164 in the text after eq . [ cstime ] ) . @xmath165 is the coefficient which depends on the specific outer and inner boundary conditions imposed in the tl ( see , titarchuk , bradshaw & wood 2001 , for details of the boundary problem of the diffusion and oscillations in tl ) . diffusion time @xmath83 is related to the diffusion length @xmath166 where @xmath167 is a free propagation path of the perturbation in the tl , @xmath168 is a number of matter interactions , related to the effective viscosity in the tl . factor @xmath169 is related to the source distribution of the perturbation in the tl ( see sunyaev & titarchuk 1985 for details ) . thus the relation between @xmath13 and @xmath9 reads as follows @xmath170 because the perturbation dimensionless depth @xmath171 is related to @xmath109 then @xmath172 thus one can find taking into account eqs.([lowfr ] , [ break - low2 ] ) that @xmath13 should not be a linear function of @xmath9 if @xmath173 . to99 found that @xmath174 when @xmath175 . the number of interactions in the tl hydrodynamical flow @xmath33 and the perturbation depth @xmath176 depends strongly on the mass accretion rate . for relatively high rates one should expect that @xmath177 and @xmath178 while these values are about one for relatively small mass accretion rates that occur in the low / hard state . in the latter case the dependence of @xmath13 on @xmath9 is almost linear . this diffusion effect is confirmed by the correlation of @xmath13 and @xmath9 observed in cyg x-1 ( see fig [ br_lowfr ] ) . for higher values of frequencies @xmath13 ans @xmath9 ( which correspond to higher values of mass accretion rate ) @xmath174 while for lower values @xmath179 . the low frequency @xmath9 is inversely proportional to the tl size which its turn is proportional to the mass of the central object @xmath180 ( bh or ns ) . thus one can conclude that @xmath9 and @xmath13 are inversely proportional to m when mass accretion rate in a source is relatively small . this inverse proportionality of @xmath13 vs @xmath181 can be used for the mass determination of the objects that mass differs by order of magnitude from galactic bhs for example , of the supermassive or intermediate bhs provided the break frequency is detected there . recently , fiorito & titarchuk ( 2004 ) applied rescaling of qpo frequency @xmath9 to evaluate a bh central mass in ultraluminous source m82 x-1 while mchardy et al . ( 2005 ) and dewangan , titarchuk & griffiths ( 2006 ) applied rescaling of @xmath13 for the bh mass determination in agn and ulx respectively .

we reveal that the spectrum of cyg x-1 consists of three components : a thermal seed photon spectrum , a comptonized part of the seed photon spectrum and the iron line . the saturation level of is the lowest value found yet in bhcs . the bolometric luminosity does not show clear correlation with the index . the ew increases from 200 ev in the low / hard state to 1.5 kev in the high / soft state . the observational correlations revealed compel us to propose a scenario for the spectral transition and iron line formation which occur in bhc sources .

we present timing and spectral analysis of 2.2 ms of rossi x - ray time explorer ( _ rxte _ ) archival data from cyg x-1 . using a generic comptonization model we reveal that the spectrum of cyg x-1 consists of three components : a thermal seed photon spectrum , a comptonized part of the seed photon spectrum and the iron line . we find a strong correlation between the 0.1 - 20 hz frequencies of quasiperiodic oscillations ( qpos ) and the spectral index . presence of two spectral phases ( states ) are clearly seen in the data when the spectral indices saturate at low and high values of qpo frequencies . this saturation effect was discovered earlier in a number of black hole candidate ( bhc ) sources and now we strongly confirm this phenomenon in cyg x-1 . in the soft state this index - qpo frequency correlation shows a saturation of the photon index at high values of the low frequency . the saturation level of is the lowest value found yet in bhcs . the bolometric luminosity does not show clear correlation with the index . we also show that fe k emission line strength ( equivalent width , ew ) correlates with the qpo frequency . the ew increases from 200 ev in the low / hard state to 1.5 kev in the high / soft state . the observational correlations revealed compel us to propose a scenario for the spectral transition and iron line formation which occur in bhc sources . we also present the spectral state ( power - law index ) evolution for eight years of cyg x-1 observations by _

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compton - thick agn ( ctagn ) are expected to constitute a significant fraction of the overall agn population in the local universe , accounting for @xmath02030@xmath10 of agn according to multiwavelength studies ( e.g. @xcite ; @xcite ; @xcite ) . many studies also predict that ctagn provide a substantial contribution to the cosmic x - ray background ( cxb ) , responsible for 1025@xmath10 of the flux at the peak energy , @xmath0 30 kev ( e.g. @xcite ; @xcite ; @xcite ; @xcite ; @xcite ) . yet , their census is still far from complete . the high line - of - sight column density in ctagn ( @xmath2 @xmath11 1/@xmath12 @xmath13 1.5 @xmath3 10@xmath4 @xmath5 , where @xmath12 is the thomson scattering constant ) , generally attributed to the parsec - scale circumnuclear torus of agn unification schemes , as well as larger - scale molecular clouds and dust lanes , results in severe attenuation of the direct x - ray emission from ctagn at energies below 10 kev . this is why observations at higher energies are needed to probe this direct component and provide unambiguous identification of ctagn . however , even at @xmath9 @xmath14 10 kev , the remaining flux that we observe in the most extreme ctagn will be from photons scattered or reflected from the back - side of the torus , and will comprise just a few percent of the intrinsic agn power ( e.g. @xcite ; @xcite ; @xcite ) . this makes the identification and characterization of ctagn a challenging task . to date , only @xmath020 agn within @xmath15 200 mpc have been confirmed as ct based upon detailed x - ray spectral characterization ( @xcite ; @xcite ; @xcite ) . this corresponds to a fraction of @xmath16 1@xmath10 of the _ total _ agn population expected within that volume , suggesting that the vast majority of ctagn are yet to be found even in the local universe . these _ bona - fide _ ctagn were unambiguously identified based upon a detection at energies above 10 kev and the presence of a fe k@xmath17 line at 6.4 kev with high equivalent width , ew @xmath1 1 kev . the identification and characterization of all the ctagn is important in order to form an accurate census of accretion in the local universe , since much of the growth of supermassive black holes is thought to occur in such heavily obscured phases ( e.g. @xcite ; @xcite ) . therefore , an accurate local benchmark is important for extrapolating the results to higher redshifts . we have started a program to study a complete , volume - limited ( @xmath18 @xmath19 15 mpc ) , mid - infrared ( mir ) selected agn sample from @xcite , with the main goal of constraining the population of ctagn and the @xmath2 distribution of agn in the local universe . ctagn candidates from the sample were identified using multiwavelength selections , such as x - ray spectroscopy , and intrinsic 210 kev luminosity indicators from high spatial resolution mir 12@xmath20 m continuum and [ o]@xmath215007 line luminosity corrected for the balmer decrement . one of the candidates that stands out in the sample as being ct based on these analyses is ngc 5643 . ngc 5643 is a nearby face - on ( _ i _ @xmath15 30@xmath22 ) sab(rs)c galaxy hosting a low - luminosity seyfert 2 nucleus ( @xcite ) . it has a redshift of @xmath23 @xmath13 0.0040 , corresponding to a metric / proper distance of @xmath18 @xmath13 13.9 mpc under the assumption of the @xcite cosmic attractor model @xcite . ngc 5643 features a compact radio core with two - sided , kiloparsec - scale lobes in an east - west orientation @xcite , and a cospatial one - sided h@xmath17 and [ o ] emission line region extending east - ward of the nucleus for at least 1.8 kpc @xcite . despite the intense star formation episodes occuring in the spiral arm , mir diagnostics suggest that the agn still dominates the overall ir ( 81000@xmath20 m ) energy budget @xcite . comparisons of optical spectra with synthesis models , however , are consistent with a starburst / seyfert 2 composite " spectrum @xcite . using br@xmath24 emission , @xcite found no on - going star formation activity in the nucleus , although the possibility of a recent ( terminated ) starburst can not be excluded . this source also shows spatially resolved molecular gas flowing out from the agn at a rate of 10 m@xmath25 yr@xmath8 @xcite . although water maser emission associated with the agn has been detected in ngc 5643 , a corresponding spatially resolved map , which would allow for a direct measurement of the supermassive black hole mass ( _ _ m__@xmath26 ) , is not yet available @xcite . however , an indirect _ _ m__@xmath26 measurement from the galaxy stellar velocity dispersion ( @xmath27 ) provides an estimated black hole mass of _ _ m__@xmath26 @xmath13 10@xmath28 m@xmath25 @xcite . estimate is obtained using an updated value of @xmath27 derived from the [ o ] @xmath215007 emission line width from @xcite and the latest _ _ m__@xmath26@xmath27 correlation by @xcite . ] in x - rays , ngc 5643 has been observed by _ asca _ @xcite , _ bepposax _ @xcite , _ rosat _ @xcite , _ chandra _ @xcite and _ xmm - newton _ ( @xcite ; @xcite ) . dramatic spectral changes were observed between the _ xmm - newton _ observation carried out in 2003 , and the _ asca _ and _ bepposax _ observations performed earlier . however , the point spread function ( psf ) of _ asca _ and _ bepposax _ were not sufficient to separate the emission of the nucleus from that of a nearby x - ray source ( at an angular separation of @xmath050@xmath29 ) , ngc 5643 x1 , which was found to be very bright at the time of the _ xmm - newton _ observation ( g04 ) . therefore , it remained unclear which source was responsible for the spectral variability observed . comparisons of the _ xmm - newton _ observations in 2003 and 2009 showed that there is no significant variation in the spectrum of the agn ( @xcite ; hereafter m13 ) . however , the off - nuclear source was found to be more than a factor of two fainter in flux in 2009 ( m13 ) than in 2003 ( g04 ) . the _ chandra _ image of the agn shows that the soft x - ray emission ( @xmath9 @xmath30 2 kev ) of the nucleus is spatially correlated with the [ o ] emission @xcite , consistent with what is commonly observed for many seyfert 2 galaxies . the dominant power source of this soft x - ray emission appears to be photoionization from the agn , although it is still unclear how much collisional ionization contributes to the overall x - ray emission ( m13 ) . above 2 kev , the x - ray spectra from these various observations show indications of the nucleus being absorbed by ct material . the evidence for this are the detection of a prominent fe k@xmath17 line ( ew @xmath14 1 kev ) and a flat photon index below 10 kev ( @xmath31 1 ) , which are characteristics of a reflection - dominated spectrum . analysis of the low signal - to - noise ratio ( s / n ) _ bepposax _ spectrum where ngc 5643 was detected only up to 10 kev , combined with an upper limit for the 15100 kev band , suggested a tentative lower limit to the column density of @xmath2 @xmath14 10@xmath32 @xmath5 @xcite . the true nature of the off - nuclear x - ray source , ngc 5643 x1 , is still uncertain . it is located in the outskirts of the host galaxy optical emission and identification of counterparts at other wavelengths has been ambiguous ( g04 ) . it is highly likely that the source is located inside the galaxy and therefore would be a powerful ultraluminous x - ray source ( ulx ) with _ _ l__@xmath33 @xmath15 1.7 @xmath3 10@xmath34 erg s@xmath8 based on the flux observed in 2003 ( g04 ) . this is comparable to the observed luminosity of the agn itself ; i.e. , _ _ l__@xmath33 @xmath15 1.9 @xmath3 10@xmath34 erg s@xmath8 ( g04 ) . lccccc instrument & obsid & date & energy band & net exposure time & net count rate + & & & ( kev ) & ( ks ) & ( 10@xmath35 cts s@xmath8 ) + ( 1 ) & ( 2 ) & ( 3 ) & ( 4 ) & ( 5 ) & ( 6 ) + _ chandra _ acis - s & 5636 & 2004 - 12 - 26 & 0.58 & 7.63 & 4.96 + _ xmm - newton _ pn / mos1 + 2 & 0601420101 & 2009 - 07 - 25 & 0.510 & 45.4/53.4 & 14.6/3.76 + _ swift_-bat & - & 2004 - 2010 & 14100 & 7340 & 0.00223 + _ swift_-xrt & 00080731001 & 2014 - 05 - 24 & 0.510 & 3.96 & 0.472 + _ nustar _ fpma / fpmb & 60061362002 & 2014 - 05 - 24 & 350 & 22.5/22.4 & 2.44/1.94 + _ nustar _ fpma / fpmb & 60061362004 & 2014 - 06 - 30 & 350 & 19.7/19.7 & 2.32/2.36 + in this paper , we present new _ nustar _ observations of ngc 5643 in which the agn and the off - nuclear source , ngc 5643 x1 , are clearly resolved and detected at hard x - ray energies ( @xmath14 10 kev ) for the first time . this allows us to provide the most accurate spectral analysis of the agn to date . the aim of this paper is to characterize the broadband spectrum of the agn by combining our _ nustar _ data with existing data from _ chandra _ , _ xmm - newton _ and _ swift_-bat . we also present the _ nustar _ data for ngc 5643 x-1 , which is detected above 10 kev for the first time . the paper is organized as follows : we describe details of the x - ray observations and data reduction of the agn in section 2 , followed by the spectral fitting procedures and results in section 3 . in section 4 , we present the data analysis and results on ngc 5643 x1 . this is followed by a discussion in section 5 . the paper concludes with a summary in section 6 .

we present two _ nustar _ observations of the local seyfert 2 active galactic nucleus ( agn ) and an ultraluminous x - ray source ( ulx ) candidate in ngc 5643 . together with archival data from however , the lack of high - quality 10 kev observations , together with the presence of a nearby x - ray luminous source , ngc 5643 x1 , had left significant uncertainties in the characterization of the nuclear spectrum . _ nustar _ now enables the agn and ngc 5643 x1 to be separately resolved above 10 kev for the first time and allows a direct measurement of the absorbing column density toward the nucleus . we also study the _ nustar _

we present two _ nustar _ observations of the local seyfert 2 active galactic nucleus ( agn ) and an ultraluminous x - ray source ( ulx ) candidate in ngc 5643 . together with archival data from _ chandra _ , _ xmm - newton _ and _ swift_-bat , we perform a high - quality broadband spectral analysis of the agn over two decades in energy (.5100 kev ) . previous x - ray observations suggested that the agn is obscured by a compton - thick ( ct ) column of obscuring gas along our line - of - sight . however , the lack of high - quality 10 kev observations , together with the presence of a nearby x - ray luminous source , ngc 5643 x1 , had left significant uncertainties in the characterization of the nuclear spectrum . _ nustar _ now enables the agn and ngc 5643 x1 to be separately resolved above 10 kev for the first time and allows a direct measurement of the absorbing column density toward the nucleus . the new data show that the nucleus is indeed obscured by a ct column of 5 10 . the range of 210 kev absorption - corrected luminosity inferred from the best fitting models is _ _ l__ ( 0.81.7 ) 10 erg s , consistent with that predicted from multiwavelength intrinsic luminosity indicators . we also study the _ nustar _ data for ngc 5643 x1 , and show that it exhibits evidence for a spectral cut - off at energy , 10 kev , similar to that seen in other ulxs observed by _ nustar_. along with the evidence for significant x - ray luminosity variations in the 38 kev band from 20032014 , our results further strengthen the ulx classification of ngc 5643 x1 .

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we observed the agn and ulx candidate in ngc 5643 using _ nustar _ on two occasions conducted at about a month separation . a summary of our main results is as follows : 1 . using the combined data from _ nustar _ , _ chandra _ , _ xmm - newton _ and _ swift_-bat , we have extended the broadband spectral analysis of the ctagn candidate in ngc 5643 to high energies ( @xmath00.5100 kev ) . using physically motivated toroidal obscuration models , we showed that the source is indeed ct with a column density of @xmath2(los ) @xmath1 5 @xmath3 10@xmath4 @xmath5 . 2 . the absorption - corrected 210 kev luminosity measured by these models is _ _ l__@xmath6 ( 0.81.7 ) @xmath3 10@xmath7 erg s@xmath8 , consistent with that predicted from multiwavelength intrinsic luminosity indicators . the luminosity inferred is at the lower end of the luminosity range of the local ctagn population . the _ nustar _ spectra of the off - nuclear source , ngc 5643 x-1 , shows evidence for a spectral cut - off at @xmath9 @xmath0 10 kev , similar to that observed in other ulxs observed by _ nustar_. combining this information with the evidence for x - ray luminosity variations observed between different observations , along with the absence of unambiguous counterparts at other wavelengths , we concluded that the source is consistent with being a ulx . future simultaneous low and high energy x - ray observations of this field are needed in order to provide higher quality data to confirm the spectral cut - off that we observed , and to better characterize the broadband spectrum of the source .

_ chandra _ , _ xmm - newton _ and _ swift_-bat , we perform a high - quality broadband spectral analysis of the agn over two decades in energy (.5100 kev ) . the new data show that the nucleus is indeed obscured by a ct column of 5 10 . the range of 210 kev absorption - corrected luminosity inferred from the best fitting models is _ _ l__ ( 0.81.7 ) 10 erg s , consistent with that predicted from multiwavelength intrinsic luminosity indicators . data for ngc 5643 x1 , and show that it exhibits evidence for a spectral cut - off at energy , 10 kev , similar to that seen in other ulxs observed by _

we present two _ nustar _ observations of the local seyfert 2 active galactic nucleus ( agn ) and an ultraluminous x - ray source ( ulx ) candidate in ngc 5643 . together with archival data from _ chandra _ , _ xmm - newton _ and _ swift_-bat , we perform a high - quality broadband spectral analysis of the agn over two decades in energy (.5100 kev ) . previous x - ray observations suggested that the agn is obscured by a compton - thick ( ct ) column of obscuring gas along our line - of - sight . however , the lack of high - quality 10 kev observations , together with the presence of a nearby x - ray luminous source , ngc 5643 x1 , had left significant uncertainties in the characterization of the nuclear spectrum . _ nustar _ now enables the agn and ngc 5643 x1 to be separately resolved above 10 kev for the first time and allows a direct measurement of the absorbing column density toward the nucleus . the new data show that the nucleus is indeed obscured by a ct column of 5 10 . the range of 210 kev absorption - corrected luminosity inferred from the best fitting models is _ _ l__ ( 0.81.7 ) 10 erg s , consistent with that predicted from multiwavelength intrinsic luminosity indicators . we also study the _ nustar _ data for ngc 5643 x1 , and show that it exhibits evidence for a spectral cut - off at energy , 10 kev , similar to that seen in other ulxs observed by _ nustar_. along with the evidence for significant x - ray luminosity variations in the 38 kev band from 20032014 , our results further strengthen the ulx classification of ngc 5643 x1 .

1205.4717

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the modelling of the spectral energy distribution ( sed ) of galaxies and its interpretation in terms of stellar population parameters ( e.g. age , star formation history , metallicity ) via stellar population synthesis ( sps ) is a fundamental tool to understand the properties and evolution of galaxies . yet , we are far from a complete comprehension and a reliable modelling of some stellar evolutionary phases which strongly affect the energy output of stellar populations . among them , the so - called thermally pulsing - asymptotic giant branch ( tp - agb ) phase has been the focus of debate among modellers for several years ( e.g. @xcite ) . this late stage of the agb phase for low and intermediate mass stars ( @xmath4 57 m@xmath5 ) culminates in stellar populations of ages between 0.5 and 1.5 gyr . tp - agb stars emit mainly in the near infrared ( nir ) spectral range given the low temperatures of these stars . quantitative predictions of the lifetimes , luminosities and spectral shapes and features of these stars as well as of their impact on the integrated spectra of even `` simple '' stellar populations , are still very uncertain and strongly model - dependent ( e.g. * ? ? ? one further complication derives from the fact that tp - agb stars are likely to be embedded in envelopes of dust produced by themselves ( e.g. * ? ? ? * ; * ? ? ? * ) , which attenuates the emerging optical and nir radiation by a substantial fraction @xcite . the seminal work of ( * ? * ma05 hereafter ) , who adopted the `` fuel consumption theorem '' approach and calibrated the flux contribution of this phase against optical and nir photometry of magellanic clouds globular clusters , dramatically pointed out how large the impact of tp - agb stars on galaxy seds may possibly be . the ma05 models make two clear and testable predictions in contrast to `` classical '' models ( such as * ? ? ? * bc03 hereafter ) , which rely on standard , less extreme prescriptions for the tp - agb phase : in particular , _ i ) _ the nir flux of stellar populations of ages between @xmath60.5 and @xmath7 gyr is enhanced by a factor up to 3 ( as a function of age and metallicity ) ; in addition , _ ii ) _ strong , sharp absorption features appear in the spectrum , especially at nir wavelengths ( and most notably at 1.1 , 1.41 and 1.77 @xmath2 m ) . these features correspond to the band - heads of carbon composite molecules and should depend on metallicity . they represent the undebatable fingerprints of tp - agb stars as predicted by ma05 models . this can be clearly seen in fig . [ fig : ma05vsbc03 ] , where we confront the optical - nir spectra of simple stellar populations ( ssp ) of three ages ( 0.5 , 1 and 1.5 gyr ) at three different metallicities ( 0.5 , 1 and 22.5 @xmath8 ) as derived from the ma05 models ( black lines ) and the bc03 models ( red lines ) respectively . observationally , detections of near - infrared cn absorption bands have been reported in the integrated spectra of only a few seyfert galaxies @xcite and globular clusters dominated by the stochastic presence of bright carbon stars @xcite . in fact , from a theoretical point of view , carbon absorption features are not a required signature of agb - star populations . sophisticated models of agb stellar evolution predict that convective dredge - up of carbon produced by nuclear fusion during the envelope thermal pulses will increase the abundance of carbon relative to oxygen near the surface , which can eventually lead to the production of a carbon star ( e.g. * ? ? ? * ) . while the efficiency of this process is expected to increase as the metallicity decreases , the integrated spectrum of most intermediate - age stellar populations could well be dominated oxygen - rich agb stars without strong carbon absorption features . the largely different nir flux predictions for tp - agb stars by different models have strong implications in terms of sed interpretation , leading to substantially lower stellar mass and age estimates ( by up to a factor 2 or more ) when rest - frame nir bands are included in the analysis of galaxies with ages around 1 gyr ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? the popularity of nir passbands as tracers of stellar mass , both at low and high redshift , thanks to their ( generally ) low sensitivity to age , metallicity and dust in terms of mass - to - light ratio ( m / l ) ( e.g. * ? ? ? * ; * ? ? ? * ) , clearly calls for a proper assessment of the models in this respect ( see also * ? ? ? verifying the reliability of sps models in the regime of ages around 1 gyr is therefore of paramount relevance for studies of galaxy properties and their evolution . since 2005 , a number of contrasting results and claims have been produced about the appropriateness of the ma05 predictions . @xcite showed that the ma05 models fit the seds of high - z ( @xmath9 ) galaxies better than bc03 models . however the same work shows that the performance of the two models differ only marginally in terms of goodness of fit if one allows for dust reddening , although the inferred stellar mass is substantially different . a better agreement of ma05 models with the observed optical - nir colours is also reported by @xcite , who used combined optical spectroscopy and optical - nir photometry to constrain the star formation history of two galaxies . @xcite also report detections of the 1.77 @xmath2 m feature in two magellanic clouds globular clusters , in agreement with ma05 predictions . on the other hand , studies of magellanic clouds globular clusters found significant discrepancies between observations and ma05 predictions . @xcite found that the co line strength ( in the nir k band ) is much weaker than predicted by ma05 in clusters of age @xmath6 1 gyr . @xcite studied the colours of magellanic clouds globular clusters as a function of their age and showed that ma05 models predict optical and nir colours that are too red . moreover the predicted age dependence of these colours does not agree with the data . as opposed , a substantial agreement with models based on much less extreme tp - agb prescriptions is found . as already pointed out by @xcite , post - starburst galaxies ( psb hereafter ) are the best galaxies to look at in order to find the fingerprints of ( tp-)agb stars on their sed . psbs have a star formation history dominated by a burst in the exact age range when tp - agb stars are expected to have the strongest impact , i.e. between 0.5 and 1.5 gyr prior to the epoch of observation . their optical spectrum is characterised by a well developed balmer / d4000 break , the lack of strong emission lines ( which testify a substantial cessation of star formation activity ) and by the very strong balmer absorption lines typical of a stars ( hence the alternative denomination of e+a or k+a galaxies ) . @xcite compared the optical - nir colours of the sample of psbs spectroscopically selected by @xcite to the colours of different sps models . they showed ( see their fig . 16 ) that @xmath10 , @xmath11 colours are not reproduced by ma05 models : not only would the blue portion of this colour plane be only explained by unrealistically low metallicities , but also the age sequences in ma05 models produce trends that are orthogonal to the observed age trends . @xcite performed another photometric test , in which they fitted the stacked ( rest - frame ) uv - optical - nir sed of 62 psbs at @xmath12 , colour selected from the _ newfirm _ medium band survey ( nmbs ) to have ages around 1 gyr , according to both bc03 and ma05 models . also in this case it is found that bc03 models can reproduce the observed seds much better , in particular the observed blue optical - nir colours , which are not reproduced by ma05 . in this paper we present the results of the experiment that we designed to test for the two main predictions of ma05 models , namely the presence of sharp nir spectral features and the boosted nir flux , on a sample of psbs carefully selected from optical spectroscopy and newly observed in nir spectroscopy ( h and k band ) with isaac at the eso - vlt . the selection criteria and properties of the sample are fully detailed in section [ sec : sample_obs ] . here we would like to stress the uniqueness of this work . _ i ) _ for the first time we cover both the optical and the nir range of psbs with flux calibrated spectra to look directly for the nir spectral features at 1.41 and 1.77 @xmath2 m predicted by the ma05 models and resulting from the large impact of tp - agb c - rich stars . these features are unaccessible or extremely difficult to measure from the ground as they roughly coincide with the atmospheric gaps between j and h , and between h and k bands , respectively , for nearby objects . therefore we observed psbs in the redshift range 0.150.25 so that the c - features move well into the observable windows and are minimally affected by uncertain telluric corrections , as shown in fig . [ fig : ma05vsbc03 ] . _ ii ) _ contrary to previous works based either on colour selection @xcite or on a purely phenomenological spectroscopic selection @xcite , the selection of our sample is based on both phenomenological criteria ( high balmer line strength and low emission lines , * ? ? ? * ) and bayesian estimates of light weighted ages from optical spectral indices as in @xcite . this allows us to focus our observations and analysis on the _ precise _ range of stellar ages where tp - agb stars are expected to contribute the most , for a variety of stellar metallicities . the paper is organised as follows . in section [ sec : sample_obs ] we present the sample , the new isaac nir spectroscopic observations and the data reduction , including spectrophotometric calibrations and integration with optical data . in section [ sec : analysis ] we present the results and discuss possible spurious effects and contaminations that might affect our conclusions . a comparison with the analysis of @xcite is also presented . finally , in section [ sec : summary ] we summarise our findings and propose our conclusions and future developments .

, we explore the parameter space over which the relative energy output of tp - agb stars peaks . our main results are : _ the optical - nir seds of most of our post - starburst galaxies can be consistently reproduced with bruzual & charlot ( 2003 ) models , using either simple stellar populations ( ssp ) of corresponding light - weighted ages and metallicities , or a more realistic burst plus an underlying old population containing up to approximately 60% of the total stellar mass .

we present vlt - isaac near infrared ( nir ) spectro - photometric observations of 16 post - starburst galaxies aimed at constraining the debated influence of tp - agb stars on the spectral energy distribution ( sed ) of galaxies with stellar ages between 0.5 and 2 gyr , hence critical for high - redshift studies . post - starburst galaxies are characterised by negligible on - going star formation and a sed dominated by the stellar population formed in a recent ( gyr ) burst . by selecting post - starburst galaxies with mean luminosity - weighted ages between 0.5 and 1.5 gyr and a broad range of metallicities ( based on sdss optical spectroscopy ) , we explore the parameter space over which the relative energy output of tp - agb stars peaks . a key feature of the present study is that we target galaxies at , so that two main spectral features of tp - agb stars ( c - molecule band - head drops at 1.41 and 1.77 m , blended with strong telluric absorption features , hence hardly observable from the ground , for targets at ) move inside the h and k atmospheric windows and can be constrained for the first time to high accuracy . our observations provide key constraints to stellar population synthesis models . our main results are : _ i ) _ the nir regions around 1.41 and 1.77 m ( rest - frame ) are featureless for all galaxies in our sample over the whole range of relevant ages and metallicities at variance with the maraston ( 2005 ) `` tp - agb heavy '' models , which exhibit marked drops there ; _ ii ) _ no flux boosting is observed in the nir . the optical - nir seds of most of our post - starburst galaxies can be consistently reproduced with bruzual & charlot ( 2003 ) models , using either simple stellar populations ( ssp ) of corresponding light - weighted ages and metallicities , or a more realistic burst plus an underlying old population containing up to approximately 60% of the total stellar mass . in contrast , all combinations of this kind based on the maraston ( 2005 ) models are unable to simultaneously reproduce the smoothness of the nir spectra and the relatively blue optical - nir colours in the observations . the data collected in this study appear to disfavour `` tp - agb heavy '' models with respect to `` tp - agb light '' ones . [ firstpage ] galaxies : stellar content stars : agb and post - agb infrared : stars infrared : galaxies galaxies : general galaxies : photometry

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we have presented the first spectroscopic study of post - starburst galaxies covering both the optical ( sdss ) and nir ( our new vlt - isaac observations ) wavelength ranges , which was specifically designed to detect the two main signatures of the presence of tp - agb stars predicted by the @xcite models in contrast to `` tp - agb light '' models ( such as bc03 ) : _ i ) _ the strong nir absorption features caused by carbon composite molecular band - heads ; and _ ii ) _ the boosting of the nir flux . to this goal , we have carefully selected a sample of 16 galaxies with post - burst ages corresponding to the peak contribution by tp - agb stars to the nir flux ( 0.51.5 gyr ) , in a broad range of stellar metallicities ( @xmath1042.5 @xmath8 ) . these galaxies are at high enough redshift ( 0.150.25 ) to allow clean measurements of the nir features at rest wavelengths 1.41 and 1.77 @xmath2 m through the atmospheric h and k windows . despite these ideal conditions for the detection of the characteristic signatures of tp - agb stars predicted by the ma05 models , the 16 galaxies in our sample all display smooth , featureless nir spectra and blue optical - nir colours . interestingly , these observed spectral properties are generally well reproduced using the bc03 models assuming simple ( i.e. single - age ) stellar populations . we have investigated whether the observations could be reproduced with ma05 models as well , by combining stellar populations of different ages . we find that diluting the light of a young ( i.e. a few 100 myr old ) starburst with that of a massive old component allows the ma05 models to reproduce the typical `` e+a '' optical spectra of post - starburst galaxies characterised by strong balmer absorption lines and a well developed d4000 break . at the same time , such models exhibit very weak nir features , in agreement with the observations , because tp - agb stars from the young component have not developed yet , while the nir emission from old stellar populations is smoother . however , these models still can not account for the data , because the predicted ratio of nir to optical flux is significantly larger than observed at the metallicity of our galaxies . hence , the observed lack of deep nir absorption features and the modest ratio of nir to optical flux in our data can not be simultaneously accounted for by a simple `` light dilution '' effect . we note that the observation of metal absorption lines at optical wavelength does not support the idea that the faint nir continuum ( and the consequent dilution and/or absence of strong nir absorption features ) could arise from extremely low metallicities . the ma05 models predict too red optical - nir colours for any choice of ratio between the old and the young component . on the contrary , models based on bc03 fail for `` old '' mass fractions as high as 90% , but produce colours that are consistent with ( most of ) the observations for `` old '' mass fractions up to 6070% , which leaves enough space to accommodate more reasonable sfhs than a ( possibly unrealistic ) single burst . we note that the work of @xcite indicates old fractions close to 90% for their seven psb galaxies , which would be inconsistent with our seds . however , this estimate might be biased by their assumption of fixed solar metallicity . moreover , and probably more importantly , it is possible that our objects are somehow more extreme in terms of burst fraction , because , due to our redshift constraints , we select objects close to the faintest limit of the spectroscopic sample of the sdss . in this way we would select the intrinsically most luminous psb galaxies at @xmath103 , hence those with the largest burst fraction ( i.e. with the lowest `` old '' fraction ) : in fact , for a given total mass , a higher burst fraction yields higher luminosity . the lack of strong colour gradients in most of our psb galaxies lends support to this hypothesis , suggesting that the starburst substantially affected the full extent of the galaxy , rather than the centre only . finally , @xcite point out that their sample is less extreme than typical samples of psb galaxies in the literature due to the small physical size of the spectroscopic fiber ( few hundred parsecs ) , which bias their selection towards central rather than extended starbursts . in conclusion , the consistency of our seds with bc03-based csps and `` old '' mass fractions up to 6070% does not raise any problem for the physical interpretation of our psb galaxies using the bc03 models . we also find that attenuation by interstellar dust , using standard prescriptions , can only worsen the disagreement ( when present ) between spectral evolution models and the observed optical - nir colours of post - starburst galaxies in our sample . this is particularly true for the ma05 models , which predict systematically redder colours than observed . we note that heavier - than - implemented attenuation by _ circumstellar _ dust of the most luminous c stars about to eject their envelopes could potentially reduce the contribution by these stars to the integrated spectrum and perhaps improve the agreement of the ma05 models with observations . a more accurate theoretical and empirical assessment of the effects of circumstellar dust absorption is definitely key to make progress in the sed modelling of the stellar population affected by tp - agb stars ( e.g. * ? ? ? * ; * ? ? ? the results presented in this work confirm the previous claim by @xcite that bc03 , and more generally `` tp - agb light '' models , provide a better agreement with the spectral properties of galaxies hosting a stellar population at the peak of the tp - agb phase than ma05 models . the important novelty of our work is to base these conclusions on a higher - resolution , high - quality spectrophotometric dataset and an optimal spectroscopic sample selection . somehow in contrast with these studies and our work in particular , @xcite have detected the 1.77 @xmath2 m feature in a couple of magellanic cloud s globular clusters and found them in agreement with ma05 predictions . this result calls for more observations in order to obtain a representative sample of globular clusters over a broader range of metallicities ( the two in which the detection was obtained are both at metallicity between 0.2 and 0.6 solar ) and beat down stochasticity effects : in fact , a single ( tp-)agb star can produce a substantial fraction of the total cluster nir luminosity in the mass range explored . one further possibility to reduce the apparent disagreement between the @xcite results and ours might reside in a technical aspect of their challenging observations : the addition of targeted agb stars outside of the central region to integrate the central spectrum and obtain full spatial coverage of the globular clusters might lead to agb stars being over - represented with respect to the stars that contribute the bulk of the diffuse emission . in the light of this complex and partly controversial observational framework , the apparent agreement of the bc03 models ( of either simple or composite stellar populations ) with the observations presented in this paper should not be necessarily interpreted as an indication that the description of the tp - agb phase in these models is adequate . new models incorporating more recent developments in the theory and observation of tp - agb stars ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) are being assembled ( charlot & bruzual , in preparation ) . by providing a better account of observations , new models of this type will allow deeper insight into the physical properties of galaxies from spectral interpretations , especially at high redshift , where a large number of galaxies is going through the evolutionary phase affected by tp - agb stars . in this perspective , the present work provides key and very stringent constraints for the new generation of stellar population synthesis models .

we present vlt - isaac near infrared ( nir ) spectro - photometric observations of 16 post - starburst galaxies aimed at constraining the debated influence of tp - agb stars on the spectral energy distribution ( sed ) of galaxies with stellar ages between 0.5 and 2 gyr , hence critical for high - redshift studies . post - starburst galaxies are characterised by negligible on - going star formation and a sed dominated by the stellar population formed in a recent ( gyr ) burst . by selecting post - starburst galaxies with mean luminosity - weighted ages between 0.5 and 1.5 gyr and a broad range of metallicities ( based on sdss optical spectroscopy ) our observations provide key constraints to stellar population synthesis models . i ) _ the nir regions around 1.41 and 1.77 m ( rest - frame ) are featureless for all galaxies in our sample over the whole range of relevant ages and metallicities at variance with the maraston ( 2005 ) `` tp - agb heavy '' models , which exhibit marked drops there ; _ ii ) _ no flux boosting is observed in the nir . in contrast , all combinations of this kind based on the maraston ( 2005 ) models are unable to simultaneously reproduce the smoothness of the nir spectra and the relatively blue optical - nir colours in the observations . the data collected in this study appear to disfavour `` tp - agb heavy '' models with respect to `` tp - agb light '' ones . [ firstpage ] galaxies : stellar content stars : agb and post - agb infrared : stars infrared : galaxies galaxies : general galaxies : photometry

we present vlt - isaac near infrared ( nir ) spectro - photometric observations of 16 post - starburst galaxies aimed at constraining the debated influence of tp - agb stars on the spectral energy distribution ( sed ) of galaxies with stellar ages between 0.5 and 2 gyr , hence critical for high - redshift studies . post - starburst galaxies are characterised by negligible on - going star formation and a sed dominated by the stellar population formed in a recent ( gyr ) burst . by selecting post - starburst galaxies with mean luminosity - weighted ages between 0.5 and 1.5 gyr and a broad range of metallicities ( based on sdss optical spectroscopy ) , we explore the parameter space over which the relative energy output of tp - agb stars peaks . a key feature of the present study is that we target galaxies at , so that two main spectral features of tp - agb stars ( c - molecule band - head drops at 1.41 and 1.77 m , blended with strong telluric absorption features , hence hardly observable from the ground , for targets at ) move inside the h and k atmospheric windows and can be constrained for the first time to high accuracy . our observations provide key constraints to stellar population synthesis models . our main results are : _ i ) _ the nir regions around 1.41 and 1.77 m ( rest - frame ) are featureless for all galaxies in our sample over the whole range of relevant ages and metallicities at variance with the maraston ( 2005 ) `` tp - agb heavy '' models , which exhibit marked drops there ; _ ii ) _ no flux boosting is observed in the nir . the optical - nir seds of most of our post - starburst galaxies can be consistently reproduced with bruzual & charlot ( 2003 ) models , using either simple stellar populations ( ssp ) of corresponding light - weighted ages and metallicities , or a more realistic burst plus an underlying old population containing up to approximately 60% of the total stellar mass . in contrast , all combinations of this kind based on the maraston ( 2005 ) models are unable to simultaneously reproduce the smoothness of the nir spectra and the relatively blue optical - nir colours in the observations . the data collected in this study appear to disfavour `` tp - agb heavy '' models with respect to `` tp - agb light '' ones . [ firstpage ] galaxies : stellar content stars : agb and post - agb infrared : stars infrared : galaxies galaxies : general galaxies : photometry

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figure [ fig9_cont ] maps the spatial distributions of gc candidates ( left panel ) and foreground / background objects ( right ) . the color - filled contours show the distribution of surface number density . the black crosses mark the positions of the optical centers of galaxies ( from top , ngc 1399 , ngc 1387 , ngc 1404 , and ngc 1389 ) . in the left panel , three gc systems are clearly visible around ngc 1399 , ngc 1404 , and ngc 1387 . the number of gcs around ngc 1389 is too small , so we omit the galaxy from the following analysis . in the right panel , the distribution of foreground / background objects appears fairly uniform . the slight overdensity in the region between ngc 1399 and ngc 1387 is likely due to the presence of a distant galaxy cluster , given that many objects in this region are bluer than 0.3 in @xmath46 . another overdense region is right on the center of ngc 1399 , which indicates that gcs in highly dense regions can be misclassified as foreground / background objects in our gc selection procedure , as mentioned in section 3 . note that the residuals of the mosaic ccd gaps are discernible as a vertical feature in the middle of the panel . it is noteworthy that the gc distribution around ngc 1399 shows interesting features . on the one hand , there is an overabundance of gcs in the outer region of ngc 1399 toward ngc 1404 and ngc 1387 . this was also pointed out by @xcite , and it may indicate interactions of ngc 1399 with ngc 1404 and ngc 1387 in the recent past ( @xcite ) . on the other hand , a @xmath505 displacement is found between ngc 1399 s optical center and the center of the gc distribution in the inner region of the galaxy as denoted by a red contour in the density map . @xcite reported an asymmetric x - ray halo for ngc 1399 , consisting of three components with different centers ; a central component , a galactic component centered 1@xmath12 southwest of ngc 1399 , and a cluster component centered @xmath556 northeast of the galaxy . while the center of the gc distribution does not coincide with the x - ray centers , the asymmetric distribution of the gcs may suggest that the ngc 1399 is not yet dynamically relaxed and may be undergoing merger events . figure [ fig10_rden ] presents the surface number densities against the galactocentric radius for the three galaxies . in order to examine the radial extent of each gc system , we calculated the surface gc number density as a function of the distance from the galaxy center . we first set up a series of radial bins ( annulus ) , each containing approximately equal numbers of gcs ( @xmath5100 gcs for ngc 1399 ; @xmath540 gcs for ngc 1404 ; @xmath525 gcs for ngc 1387 ) . the number of gcs in each bin was then corrected using the corresponding completeness function of the bin . we finally divided the corrected numbers of gcs by the area of annuli to get surface densities . the surface density profile of each galaxy is well described by de vaucouleurs @xmath58 fits ( dashed lines ) . we determine the limiting radii of gc systems of ngc 1404 ( 34 ) and ngc 1387 ( 37 ) as the radial points where the density profiles begin to depart from de vaucouleurs law . since the gc system of ngc 1399 is extended ( @xmath545 ; @xcite ) well beyond the field of view ( @xmath59 ) of our mosaic observations , we regard the entire gcs in the images as ngc 1399 s gc system , except for the regions inside the limiting radii of ngc 1404 and ngc 1387 . figure [ fig11_cmd ] presents the cmds for all point - sources . magnitudes and colors were corrected for the galactic extinction , as mentioned in section 2.3 . the black and gray dots represent the gc candidates and foreground / background objects , respectively . the dashed lines indicate the limiting magnitude of 50% completeness . the tilt of the limiting magnitude lines results from lower detection efficiency of red gcs than blue gcs in the @xmath0 band . the @xmath46 colors corresponding to gcs , background galaxies , and foreground stars can be determined both by the @xmath46 versus @xmath47 diagram ( the bottom panel of figure [ fig6_twocol ] ) and by the @xmath4@xmath46 cmd ( the left panel of figure [ fig11_cmd ] ) . gcs are placed at @xmath60 , while most background galaxies are bluer at @xmath46 @xmath61 @xmath62 and foreground stars are at @xmath63 and 1.1 close to both ends of the gc range . the @xmath4@xmath44 cmd ( right panel ) shows that many of the background galaxies have similar colors to the gcs , making it difficult to discriminate gcs from galaxies in this color . the foreground star sequences , particularly on the red side , are more clearly separated from gcs than in @xmath46 . this comparison corroborates that the use of various color combinations including @xmath0-band colors provides a powerful tool for discriminating gcs from other objects . it is interesting to note that the cmds do not show bimodality for gcs brighter than @xmath64 . the disappearance was previously reported for ngc 1399 ( @xcite ) , a few galaxies in the virgo cluster ( @xcite ) , and other giant galaxies ( @xcite ) . the unimodal distribution is often explained by merging of blue and red sequences at the highest luminosities as a result of the blue tilt phenomenon @xcite , which is a trend for the blue gcs to have redder colors at higher luminosities . however , @xcite and @xcite have reported that there is no blue tilt in the gc system of ngc 1399 . interestingly , our data reveal that the number of blue gcs rapidly drops at the brightest magnitudes ( @xmath4 @xmath39 21.5 ) . this suggests that the unimodal distribution of brightest gcs is not the consequence of the blue tilt , but instead owing to the relative scarcity of blue , brightest gcs . figure [ fig12_colhist ] shows three representative color histograms of the entire gc system within the limiting radius in ngc 1399 ( top ) , ngc 1404 ( middle ) , and ngc 1387 ( bottom ) . the gcs fainter than the limiting magnitudes and/or the ones located in the innermost region of each galaxy , where the completeness test is unreliable ( see section 2.3 ) , are taken out from the subsequent analysis . the thick solid lines are smoothed histograms with gaussian kernels . the filled histograms in the top row are for the brightest gcs , as mentioned in the previous section . for ngc 1399 ( top row ) , gcs show bimodal distributions for all colors considered in agreement with previous findings in @xmath11 ( @xcite ) . for ngc 1404 ( middle ) and ngc 1387 ( bottom ) , the dotted histograms are for all gcs within the limiting radii of the galaxies . the solid histograms represent `` corrected '' distributions , for which the contribution of ngc 1399 gcs is statistically subtracted from the original distributions and will be used in the further analysis . ngc 1404 gcs exhibit pronounced bimodality with an evident dip between two groups in all colors , consistent with the previous studies for ngc 1404 s inner gcs by @xcite and @xcite . the clear separation between blue and red gcs for ngc 1387 gcs is also consistent with what was found in @xmath11 by @xcite . blue gcs are much less abundant in ngc 1404 and ngc 1387 than in ngc 1399 . a closer scrutiny of figure [ fig12_colhist ] reveals that the exact morphologies of the gc color distributions change depending on colors considered . the most distinctive case is given by the @xmath46 distribution of ngc 1399 . compared to the @xmath44 and @xmath65 histograms , the @xmath46 distribution exhibits more prominent blue gc peak and have red gcs with weaker peak and larger dispersion in color . the @xmath46 distribution shows spread in colors of red gcs that is nearly a factor of two larger than that of blue gcs , while the @xmath44 and @xmath65 histograms have similar variances for the red and blue gcs . the histograms for ngc 1404 and ngc 1387 also show changes in their shape depending on colors . to be more quantitative in the bimodality analysis , we used the gaussian mixture modeling ( gmm ) code by @xcite . table [ tbl - gmm ] presents the results of the gmm analysis for six color combinations ( @xmath46 , @xmath45 , @xmath66 , @xmath44 , @xmath47 , and @xmath65 ) for the three galaxies . it gives the color index , the mean ( @xmath67 , and the standard deviation ( @xmath68 ) of blue and red gc colors , the red gc fraction ( @xmath69 ) , and the ratio of the standard deviations between blue and red gcs ( @xmath70/@xmath71 ) . the last three columns summarize the probabilities of preferring a unimodal distribution over a bimodal distribution ( @xmath72-values ) derived based on the likelihood ratio test ( lrt ; @xmath73 ) , on the separation of the means relative to their variances ( @xmath74 ) and on the kurtosis of a distribution ( @xmath75 ) . from the lrt is @xmath76 in all colors , indicating the bimodal distributions are preferred over the unimodal ones . the @xmath77 values lead to the same conclusion in all cases . the @xmath78 values support the bimodal distributions in most cases , but favor a unimodal distribution for @xmath46 of ngc 1399 with @xmath79 . ] figure [ fig13_tab4 ] presents the results from the gmm analysis for all six color combinations . to quantify the shape of histograms , we use the red gc fractions ( left ) and the ratios of standard deviations between blue and red gc colors ( right ) . ngc 1399 gc sample ( black solid lines ) does not include gcs around ngc 1404 and ngc 1387 , and the gc sample of ngc 1404 ( red dashed lines ) and ngc 1387 ( blue dotted ) is corrected for ngc 1399 gc contribution . for ngc 1399 , we find that both the numbers and dispersions of blue and red gcs change significantly depending on colors that are used . the trend is more evident when comparing the @xmath0-band colors with the rest . for ngc 1404 and ngc 1387 , the interesting features emerge after the correction for the contribution of ngc 1399 gcs . first , the red gc fractions in all colors remain constant regardless of the colors , as expected in figure [ fig12_colhist ] showing distinct separation between blue and red gcs . it is plausible that the early interactions of the galaxies with ngc 1399 have preferentially left the central , red gcs and later blue gcs have been accreted from outer region of ngc 1399 . second , the color dispersions vary significantly depending on colors , following a similar pattern to the case of ngc 1399 for @xmath16 , @xmath28 , and @xmath15 . for @xmath0-band colors , however , the patterns are different in the sense that they tend to be constant within the errors . the variation of dispersion as a function of colors is not expected if the metallicity - to - color converting relations are straight . instead , the slopes seem different between the blue and red parts of the metallicity color relations and such an effect varies systematically from color to color ( @xcite ) . figure [ fig14_n1399h ] displays the color distributions as a function of galactocentric radius for gcs in ngc 1399 . the subsequent analysis is only valid for ngc 1399 because small number statistics prohibit us making any firm statement on the radial variations of gc colors for the two fainter galaxies after the correction for the ngc 1399 gc contamination . in order to investigate the radial variation of color bimodality , we set up a series of radial bins containing approximately equal number ( @xmath5300 ) of gcs and perform the gmm analysis for each bin . we focus particularly on three main parameters of the gmm analysis that characterize the bimodal distributions ; the number ratio between blue and red gcs , the mean colors of the groups , and their color dispersions . figure [ fig15_n1399r ] shows the variations of color bimodality properties as a function of galactocentric radius . there is an obvious radial trend for the mean colors of both blue and red gcs getting bluer with increasing radius in all colors . the radial color gradient of red gcs is steeper than that of blue gcs . the red gc fraction in each color rapidly decreases with increasing galactocentric radius out to @xmath80 @xmath61 @xmath81 , and it remains fairly constant beyond the point . there is a weak radial trend in gc color dispersions , in that the ratio between dispersions of blue and red gcs increases with radius .

the main results based on some 2000 gc candidates around ngc 1399 , ngc 1404 , and ngc 1387 are as follows : ( 1 ) the gc system in each galaxy exhibits bimodal color distributions in all colors examined , but the shape of color histograms varies systematically depending on colors ; ( 2 ) ngc 1399 shows that the mean colors of both blue and red gcs become bluer with increasing galactocentric radius ; ( 3 ) ngc 1399 shows overabundance of gcs in the directions of ngc 1404 and ngc 1387 , indicating their ongoing interactions ; and ( 4 ) ngc 1399 also exhibits a offset between the center of the inner gc distribution and the galaxy s optical center , suggesting that ngc 1399 is not yet dynamically relaxed and may be undergoing merger events .

we present wide - field multiband photometry of globular cluster ( gc ) systems in ngc 1399 , ngc 1404 , and ngc 1387 located at the central region of the fornax galaxy cluster . observation was carried out through , , , and bands , which marks one of the widest and deepest-band studies on extragalactic gc systems . the present-band photometry enables us to significantly reduce the contamination by a factor of two for faint sources (.5 ) . the main results based on some 2000 gc candidates around ngc 1399 , ngc 1404 , and ngc 1387 are as follows : ( 1 ) the gc system in each galaxy exhibits bimodal color distributions in all colors examined , but the shape of color histograms varies systematically depending on colors ; ( 2 ) ngc 1399 shows that the mean colors of both blue and red gcs become bluer with increasing galactocentric radius ; ( 3 ) ngc 1399 shows overabundance of gcs in the directions of ngc 1404 and ngc 1387 , indicating their ongoing interactions ; and ( 4 ) ngc 1399 also exhibits a offset between the center of the inner gc distribution and the galaxy s optical center , suggesting that ngc 1399 is not yet dynamically relaxed and may be undergoing merger events .

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we have performed wide - field @xmath30 photometry of gcs in the central region of the fornax cluster of galaxies with the mosaic ii ccd imager on the 4 m blanco telescope at ctio . this is one of the widest and deepest @xmath0-band studies on extragalactic gc systems . the reduction was carried out with the daophot ii / allframe package . using two - color diagrams and the magnitude cut of @xmath82 , a total of 2037 gc candidates were selected among 12,134 objects detected in all four bands . our estimate of the contamination by background galaxies and foreground stars in our sample is in the range of 9%16% . the sample is @xmath0-band limited , and the completeness of our photometry is 50% at @xmath83 according to our artificial star tests . we provide the @xmath30 photometric catalog of the gc candidates online . for the gc systems of ngc 1399 , ngc 1404 , and ngc 1387 , we have investigated the spatial distributions , cmds , and color distributions . for ngc 1399 gcs , the radial variations in the properties of bimodality were examined as well . the main results are summarized as follows . 1 . we find an asymmetric distribution of gc candidates around ngc 1399 . the overabundance of gcs at the southeast side of the inner region and toward the directions of ngc 1404 and ngc 1387 in the outer region suggests that there were recent interactions of ngc 1399 with the galaxies and that ngc 1399 is not yet dynamically relaxed . we specify the radial extent of each gc system at the radius where the surface density profile begins to depart from the de vaucouleurs fit . the limiting radii are @xmath534 for ngc 1404 and @xmath537 for ngc 1387 . the gc system of ngc 1399 is spatially extended beyond the field of view of our observation . we show that the gc systems in the three galaxies exhibit bimodal color distributions in all the colors considered in this study . for the brightest gcs in ngc 1399 , the bimodality becomes weak or disappear depending on colors . we find with gmm that the morphology of the color histograms changes significantly , depending on the colors used . the color dispersion of red gcs is larger than that of blue gcs in @xmath0-band colors by more than a factor of two , while the red and blue gcs show similar dispersions in @xmath44 and @xmath65 . the number ratios between blue and red gcs vary depending on colors used as well . when corrected for the contribution of ngc 1399 gcs , the red gc fractions of ngc 1404 and ngc 1387 remain constant regardless of the colors used . we suggest a possible scenario that could explain the presence of two discrete gc populations in ngc 1404 and ngc 1387 : ( 1 ) the central , red gcs have been preferentially left through the early interactions of the galaxies with ngc 1399 and ( 2 ) later blue gcs have been accreted from outer region of ngc 1399 . we confirmed that the mean colors of blue and red gcs in ngc 1399 show a radial trend of becoming bluer with increasing galactocentric radius . the gradient of red gcs is steeper than that of blue gcs . acknowledges support from international exchange program for university researchers ( nrf-2011 - 013-c00031 ) and from mid - career research program ( no . 2012r1a2a2a01043870 ) through the national research foundation ( nrf ) of korea grant funded by the ministry of education , science and technology ( mest ) , and support by the nrf of korea to the center for galaxy evolution research ( no . 2012 - 8 - 1743 ) and by the korea astronomy and space science institute research fund 2011 and 2012 . this work is partially supported by the kasi - yonsei joint research program ( 20112012 ) for the frontiers of astronomy and space science funded by the korea astronomy and space science institute . this material is based upon work supported by aura through the nsf under aura cooperative agreement ast 0132798 , as amended . bassino , l. p. , faifer , f. r. , forte , j. c. , et al . 2006 , , 451 , 789 bassino , l. p. , richtler , t. , & dirsch , b. 2006 , , 367 , 156 bekki , k. , forbes , d. a. , beasley , m. a. , & couch , w. j. 2003 , , 344 , 1334 blakeslee , j. p. , cho , h. , peng , e. w. , et al . 2012 , , 746 , 88 blakeslee , j. p. , jordn , a. , mei , s. , et al . 2009 , , 694 , 556 bridges , t. j. , hanes , d. a. , & harris , w. e. 1991 , , 101 , 469 cantiello , m. , & blakeslee , j. p. 2007 , , 669 , 982 cardelli , j. a. , clayton , g. c. , & mathis , j. s. 1989 , , 345 , 245 chies - 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we present wide - field multiband photometry of globular cluster ( gc ) systems in ngc 1399 , ngc 1404 , and ngc 1387 located at the central region of the fornax galaxy cluster . the present-band photometry enables us to significantly reduce the contamination by a factor of two for faint sources (.5 ) .

we present wide - field multiband photometry of globular cluster ( gc ) systems in ngc 1399 , ngc 1404 , and ngc 1387 located at the central region of the fornax galaxy cluster . observation was carried out through , , , and bands , which marks one of the widest and deepest-band studies on extragalactic gc systems . the present-band photometry enables us to significantly reduce the contamination by a factor of two for faint sources (.5 ) . the main results based on some 2000 gc candidates around ngc 1399 , ngc 1404 , and ngc 1387 are as follows : ( 1 ) the gc system in each galaxy exhibits bimodal color distributions in all colors examined , but the shape of color histograms varies systematically depending on colors ; ( 2 ) ngc 1399 shows that the mean colors of both blue and red gcs become bluer with increasing galactocentric radius ; ( 3 ) ngc 1399 shows overabundance of gcs in the directions of ngc 1404 and ngc 1387 , indicating their ongoing interactions ; and ( 4 ) ngc 1399 also exhibits a offset between the center of the inner gc distribution and the galaxy s optical center , suggesting that ngc 1399 is not yet dynamically relaxed and may be undergoing merger events .

hep-th0207057

i

we address the question of how the dynamics of quantum systems on curved space times can be described in a physically motivated and mathematically useful manner in the special case of a class of robertson walker space times . in the literature known to us , the general question is broached either for free fields or in some quasi - classical approximation . we would like to give a purely quantum field - theoretic treatment which is valid also for interacting quantum fields . we do so in the language of algebraic quantum field theory@xcite , which , though not widely known , has the advantages of being conceptually broad enough to subsume within it most approaches to quantum field theory and yet being mathematically rigorous . corresponding to the operationally motivated nature of algebraic quantum field theory , we begin our considerations with the worldline of an observer . this moving observer is subject to various forces if his worldline is a geodesic , these forces are purely gravitational ; otherwise , he is subject to acceleration due to non - gravitational causes . the same is true if the worldline is that of a quantum system , subject now to forces on the quantum level . what would be a suitable , mathematically rigorous description of the attendant dynamics of this system ? we propose an answer to that question , at least for quantum systems on a large class of robertson walker space times , which includes de sitter space . in section 2 , we shall specify the class of robertson walker space times we shall be considering . for all of these space times , the local conformal group is @xmath0 . we show that given an arbitrary worldline in such a space time , two physically motivated assumptions allow us to find a unique curve in @xmath0 which generates the worldlines of the given system and neighboring systems . these considerations are purely geometrical in nature . quantum theory enters for the first time in section 3 , where we describe quantum systems on our class of robertson walker space times using nets of local observable algebras supplied with a state . we define there what we mean by covariant , respectively quasi - covariant , dynamics of such systems . this will involve continuous 2-parameter families of automorphisms of the global observable algebra satisfying canonical propagator identities , which implement the action of the curve in @xmath0 associated with the evolution of the initial worldline , and which act locally on the observables in a well motivated manner . in section 4 , we shall use results from a previous paper @xcite to construct nets and states on the specified robertson walker space times which admit dynamics in the sense of section 3 . we provide examples which admit covariant dynamics , as well as examples which only admit quasi - covariant dynamics . the transplanted state will be shown to be passive in an appropriate sense for this dynamics , so that for this dynamics the state behaves like a local equilibrium state from which cyclic processes can not extract energy . in the final section , we shall discuss the relation between our work and an alternate proposal for dynamics of quantum systems on curved space times made by keyl@xcite . we shall also make some remarks about the further outlook of this program . an appendix contains proofs of a more technical nature .

we propose a canonical description of the dynamics of quantum systems on a class of robertson walker space times . we show that the worldline of an observer in such space times walker space that there exist quantum systems on robertson the transplanted state is locally passive , in an appropriate sense , with respect to this dynamics .

we propose a canonical description of the dynamics of quantum systems on a class of robertson walker space times . we show that the worldline of an observer in such space times determines a unique orbit in the local conformal group of the space time and that this orbit determines a unique transport on the space time . for a quantum system on the space time modeled by a net of local algebras , the associated dynamics is expressed via a suitable family of `` propagators '' . in the best of situations , this dynamics is covariant , but more typically the dynamics will be `` quasi - covariant '' in a sense we make precise . we then show by using our technique of `` transplanting '' states and nets of local algebras from de sitter space to robertson walker space that there exist quantum systems on robertson walker spaces with quasi - covariant dynamics . the transplanted state is locally passive , in an appropriate sense , with respect to this dynamics .