bluuebunny/crossref_metadata_2025 huggingface dataset:
New Radio Observations Of ‘Old Faithful’
Authors: Porcas R.W. , Patnaik A.R. , Muxlow T.W.B. , Garrett M.A. , Walsh D.
Published: July 2016

We present new arcsecond-scale radio images of the gravitational lens system 0957+561 A, B. Observations at 1.6GHz were made in 1991 October with the VLA in A/B configuration with a resolution of 1.5 arcsec (Fig. 1, left). The lowest contour is 0.37 mJy/beam. In addition to the compact A and B image components, and the familiar NE/SW radio double-lobe structure surrounding image A, this map shows two interesting new features:

(a)

a long, thin feature extending south and west from the NE lobe, some 10 arcsec in extent, confirming the detection by Avruch et al. (1994). It is reminiscent of the ‘arc’ features seen in optical images of lensing clusters, and hopefully can be used to constrain models of the cluster mass distribution. (For the superstitious, one can note that the position angle of the arc, 17°, is identical to that of the VLBI jet in image B, a few arcseconds to the west.)

(b)

a low-level extension of the B image in the NW direction. We are not aware that this has been seen before. A possible interpretation of this feature is a continuation of the jet emission seen in VLBI images of B, whose counterpart in A is seen in higher resolution maps. The change of position angle between the VLBI and arcsec-scale jets would indeed have opposite parities in the A and B images.
A Gravitational Lens Candidate Behind The Fornax Dwarf Spheroidal Galaxy
Authors: Tinney C.G.
Published: July 2016

CCD astrometry makes possible milli-arcsecond precision relative astrometry at faint magnitudes (Tinney 1994a). The measurement of proper motions for the nearest galaxies is therefore a project requiring only years – not decades. A prerequisite for such measurements, however, is a set of unresolved, extragalactic reference objects – ie. QSOs. While searching for such objects behind the Fornax dSph galaxy, Tinney (1995b) discovered the QJ0240-343AB system as a pair of bright, UV-excess objects (U-B = −1.0, B = 19.0 & 19.8) with a separation of 6.1″. Spectra obtained with the 3.9 m Anglo-Australian telescope and the RGO+FORS spectrographs (Fig. 1) have shown both components of the pair to be at a redshift of z = 1.4, with a rest velocity difference consistent with zero at a 1-σ limit of 180 km/s. The spectra also show a definite metal-line absorption system at z = 0.543 and a possible system at z = 0.337. No bright lens is seen, but the strong similarities in the spectra suggest a gravitational lens nature.
Preliminary VLA Snapshots of Southern Radio Sources from the Parkes-MIT-NRAO (PMN) Survey
Authors: Fletcher A. , Burke B. , Conner S. , Herold L. , Cooray A. , Haarsma D. , Crawford F. , Cartwright J.
Published: July 2016

Selection criteria for 1800 MIT-VLA snapshots of PMN radio sources are described, and 6 new MG & PMN lens candidates are presented.
Summary of Data on Secure Multiply Imaged Systems
Authors: Keeton C.R. , Kochanek C.S.
Published: July 2016

We present an extensive summary of the position, redshift, and flux data on the secure, multiply imaged, quasar and radio lenses. It includes neither the less-promising (in the opinion of the author) lens candidates nor the cluster lenses (which are too hard to reduce to short tables of numbers). A broader listing of suggested lenses and also of the cluster lenses is available at (see Pospieszalskia-Surdej et al. in this volume): http://www.stsci.edu/ftp/stsci/library/grav_lens/grav_lens.html
The Stellar Population of the Galactic Bulge
Authors: Rich R. Michael
Published: July 2016

How old is the bulge? Are bulges in general as old as halos? Do bulges form rapidly or slowly? Are they formed from disks via dynamical instabilities, or perhaps by starbursts? In general, do luminous spheroids form at the same time as the oldest stars?
Chemo-Dynamical Models and the Star Formation History of Galaxies
Authors: Samland M. , Hensler G.
Published: July 2016

Sandage (1986) showed what the star formation rate (SFR) of galaxies of different Hubble type might look like. His curves are based on the study of Gallagher et al. (1984), who determined the SFR at three different epochs of galactic evolution. Sandage's figure establishes a connection of SFR and Hubble type but, as was already mentioned by Sandage, it “contains no physics”. In order to explore the background of this connection, however, it is necessary either to improve the observations or to model the evolution of galaxies self-consistently. However, the results of modelling the SFR are not reliable, if simplified models are used, which only describe some structural properties of galaxies. It is necessary to apply self-consistent models which take into consideration all relevant interaction processes between the gaseous and stellar components of a galaxy. Such models can be checked by comparison with observations like density and abundance distributions, star-gas content, velocities, velocity dispersions, mass-luminosity relations and age distributions of stars. A detailed model will show, whether the initial conditions, the feedback mechanisms during the evolution or the environment determine the evolution of a galaxy.
Hot Gas Flows in Elliptical Galaxies
Authors: Renzini Alvio
Published: July 2016

Stars in elliptical galaxies lose mass at an overall present rate Ṁ∗ ≃ 1.5 × 10−11LBM⊙yr−1 (e.g., Faber & Gallagher 1976; Renzini & Buzzoni 1986). When allowing for the predicted increase back with cosmological time it turns out that over one Hubble time the stellar population of an elliptical galaxy has cumulatively lost 20-50% of its initial mass, the precise value depending on the IMF. This review focuses on two simple questions: what happens to the gas being lost by the stars? Where is it ultimately disposed?
Mergers and the Formation of Massive Ellipticals
Authors: Bender Ralf
Published: July 2016

Many nearby luminous elliptical galaxies exhibit counter-rotating cores, minor axis rotation or peculiar velocity fields. These phenomena require that merging and accretion events played a major role in the formation of ellipticals and, equally important, that stars dominated significantly over gas in the merger progenitors. Low redshift analogues to the last stages in the formation of massive ellipticals can be observed in ultraluminous IRAS mergers. However, this does not imply that ellipticals generally formed in spiral-spiral mergers. Mergers can also occur as a consequence of inhomogenous collapse or hierarchical bottom-up structure formation and it is actually more likely that the progenitors of present-day ellipticals did not resemble present-day spirals.

Although some ellipticals most certainly were and still are formed at low redshift, the general formation epoch of massive ellipticals is likely to be found at redshifts > 1. The evidence for this is threefold: (a) the homogenous stellar populations of ellipticals, most notably the tight correlation between colors/absorption linestrengths and velocity dispersion, (b) the high overabundance of light elements relative to iron and (c) the very weak evolution of colors and linestrengths of ellipticals with redshift.
Dynmamical Effects on Galaxies in Clusters
Authors: Moore Ben , Katz Neal , Lake George
Published: July 2016

For nearly 20 years, we've known that clusters at z≳0.3 have a substantial population of “blue galaxies” seen only as fuzzy blobs in ground based images (Butcher & Oemler 1978, 1984). Hubble Space Telescope (HST) images reveal that these “fuzzy blue blobs” are low luminosity, often disturbed, spiral galaxies “Sp” (Dressier et al 1994a,b, Couch et al 1994). Today, rich galaxy clusters are dominated by elliptical “E” and lenticular “S0” galaxies (Dressier 1980), mostly low luminosity dwarfs.
The Evolution of Field Galaxies
Authors: Lilly S.J. , Le Fevre O. , Hammer F. , Crampton D. , Schade D.J. , Hudon J.D. , Tresse L.
Published: July 2016

During the late 1980's, successively deeper redshift surveys carried out with
multi-object spectrographs on 4-m class telescopes produced growing evidence for evolution in the galaxy population. While some evolution had been expected from analysis of the galaxy number counts, the surprising indication from the first deep redshift surveys was that this appeared to involve moderate luminosity galaxies lying at moderate redshifts (Broadhurst et al. 1988, Colless et al. 1990, Cowie et al. 1991). However, while the results were suggestive, these early surveys suffered a number of significant problems that hampered their interpretation:

(a)

the samples were small, especially at the faintest levels, so the statistical weight was limited and analysis was based on crude parameterizations of the data such as the median redshift of samples;

(b)

the typical redshifts were small (z << 0.5), so that evolutionary effects could only be seen against “local” populations whose selection was often quite different - indeed the local luminosity function of galaxies is still poorly defined (Loveday et al. 1992, Marzke et al. 1994);

(c)

the samples were selected in the observed B-band, so that comparison with local samples was based on the poorly constrained ultraviolet properties and relative numbers of galaxies of different types.
A Glimpse of Field Galaxies at Redshifts z ∼ 1 using HST and the Keck Telescope
Authors: Koo D. C.
Published: July 2016

Data from the Keck and Hubble Space Telescopes have been combined to explore the nature of very faint I > 22 field galaxies. At a redshift z ∼ 1, such galaxies have luminosities similar to that of typical galaxies today. Though small, our sample of 33 redshifts already suggest that the median redshift for I > 22 galaxies is higher than the z = 0.6 expected for the “maximum merger model” of Carlberg (1995). At redshifts z > 0.8, mergers, interactions, and infall of minor galaxies into larger hosts appear to be common events; a wide diversity of morphological types existed; and some stellar populations were already so red that their major formation epoch occurred at redshifts z > 2.
Faint Galaxy Number-Counts
Authors: Metcalfe N. , Shanks T. , Fong R. , Gardner J. , Roche N.
Published: July 2016

Observers studying the cosmology and evolutionary history of our Universe through the statistical properties of ‘normal’ galaxies have four main tools at their disposal. (1) The number-redshift relation. Although a very powerful diagnostic, spectroscopic surveys are currently limited to B < 24m and significantly incomplete in the range, 23m< B < 24m. (2) Galaxy number-magnitude counts. Although by themselves, they cannot constrain models as tightly as spectroscopy, they can be measured ∼ 4m fainter, where cosmological effects are expected to be significant. (3) Galaxy colours over a wide wavelength range, which provide additional constraints. (4) The dependence of galaxy clustering with magnitude. ω(θ) can be measured to the limit of the counts.

Here we report on the latest Durham count and clustering work.
The Quest for Protogalaxies
Authors: Djorgovski S.G.
Published: July 2016

The current state and the future prospects of searches for protogalaxies (PGs) are reviewed. Many high-redshift objects are now known, mostly associated in some way with AGN, and at least some of them may be young galaxies. Quasars at z > 4 and high-z quasar pairs may mark galaxy formation sites. Deep field surveys for Lyα luminous galaxies powered by star formation alone have failed so far to reveal a large population of such objects, and the observed limits are in conflict with simple model predictions by three orders of magnitude. Some extinction by dust can account for this. However, strong limits from COBE place severe constraints on models of completely obscured PGs. New searches in the near IR are now beginning to probe the relevant line flux and number density regime, and first interesting PG candidates are being discovered. Searches from mid-IR to mm wavelengths would complement these efforts.
Search for Primeval Galaxies with the “Calar Alto Deep Imaging Survey”
Authors: Hippelein H. , Meisenheimer K. , Thommes E. , Fockenbrock R. , Röser H.-J.
Published: July 2016

Understanding the formation of galaxies is certainly one of the major challenges in astrophysics. Observationally, the most important insight will be provided by the detection and study of primeval galaxies. With the large telescopes and the efficient detectors available today, it seems feasible to observe those early stages of galaxy evolution directly. Despite considerable efforts with different techniques (Cowie et al. 1990; De Propris et al. 1993; Pritchet & Hartwick 1990; Thompson et al. 1995; Djorgovski et al. 1993) no primeval galaxy is found yet, in contradiction with predictions by model calculations (e.g. Baron & White 1987). What could be the reason for this lack of sucess?
Results from Searches for High-Redshift Galaxies around Damped Lyα Systems
Authors: Warren S. J. , Møller P.
Published: July 2016

There was not much said at this conference about the damped Lyα absorbers, yet locally and at high redshift nearly all the neutral hydrogen in the Universe lies in the damped systems, so they may have much to tell us about when and how galaxies formed. This talk is concerned with the results of narrow-band imaging searches for Lyα emission from, and around, damped Lyα absorbers. There have been many such searches, but very few detections. Here we concentrate on two groups of galaxies at high redshift, z > 2, found by this technique. One of these is a recent discovery (Francis et al. 1995), and for the other we discuss some new observations (Warren and Møller 1995). A study of these two groups provides some clues to the nature of the damped absorbers at high redshift, and the rôle they play in the formation of galaxies.
Galaxy Evolution from QSO Absorption-Line Selected Samples
Authors: Dickinson Mark , Steidel Charles C.
Published: July 2016

Although a connection between certain classes of QSO absorption line systems and gas associated with galaxies was hypothesized long ago, the first systematic evidence supporting this was provided by Bergeron & Boissé (1991). Observing QSOs with known Mgll absorption lines at zabs < zQSO, they identified galaxies near the QSO sightline and spectroscopically confirmed that their redshifts matched those of the MgII absorption doublet.
The host Galaxies of z ≈ 2 Radio-Quiet QSOS
Authors: Aretxaga Itziar , Boyle B.J. , Terlevich R.J.
Published: July 2016

Based on an R-band imaging survey of high-redshift (z ≈ 2) QSOs with the 4.2m WHT, we report the detection of extensions to the nuclear PSFs of two radio-quiet and one radio-loud QSO. The extensions are most likely host galaxies, with luminosities of at least 3 – 7% of the QSO luminosity. The most likely values for the luminosities lie in the range 6 – 18% of the QSO luminosity (R ∼ 19.8 – 20.9 mag). Our observations show that, if the extensions we have detected are indeed galaxies, extraordinary massive and luminous galaxies are not only characteristic of radio-loud objects, but of QSOs as an entire class. For a detailed description of this work, see Aretxaga, Boyle & Terlevich (1995) MNRAS, 275, L27.
Starburst Cycle in Distant Clusters
Authors: Barger A.J. , Aragón-Salamanca A. , Ellis R.S. , Couch W.J. , Smail I. , Sharples R.M.
Published: July 2016

A major puzzle in observational cosmology is the physical origin of a significant excess population of blue galaxies in the cores of distant rich galaxy clusters. This ‘Butcher-Oemler’ effect is now known to be a widespread starburst-related phenomenon. We test whether various spectral and photometrically-defined galaxy classes might represent different stages within a single cycle of star-formation. We compare the numbers of galaxies in various categories for three z = 0.31 clusters, AC103, AC114, and AC118, with evolutionary models generated according to the Bruzual & Chariot (1993) isochrone spectral synthesis code, assuming that some fraction of the model cluster population is viewed either before or during a secondary burst of star formation. We find good agreement between the model predictions and the number density of spectroscopically-confirmed members in the H δ versus B – R plane for a cluster population in which 30 per cent of the member galaxies have undergone secondary bursts of star formation within the last ∼ 2 Gyr prior to observation. As an additional check, we analyse a larger Kn–limited sample from newly-acquired infrared images and find good agreement between the models and the data in the U – I versus I – Kn plane for the same active cluster fraction. We conclude that the unusual galaxy population in distant clusters can be explained by a single cycle in which about 30 per cent of the cluster population experienced a secondary burst of star-formation within the last ∼ 2 Gyr.
HI in HII–Galaxies and their Companions
Authors: Brinks E. , Taylor C. L. , Thomas D. L. , Skillman E. D.
Published: July 2016

HII galaxies are dwarf galaxies which are currently actively forming stars. We speculated that an interaction with an optically faint, but gas-rich object might be responsible for their enhanced star formation. This prompted us to search for companions with the VLA in the 21–cm line of HI. This has several advantages over optical searches (Campos–Aguilar et al. 1991, AJ, 106, 1784; Telles & Terlevich 1995, MNRAS, 275, 1), e.g., the direct availability of redshifts.
Isophotal Effects in Faint Galaxy Samples
Authors: Bristow P. , Philllipps S.
Published: July 2016

Using Monte Carlo style simulations of galaxy populations we create artificial faint galaxy samples which mimic those obtained by actual observational techniques. By comparison of samples selected according to total luminosity or luminosity within an isophote we are able to estimate the extent to which isophotal effects could cause number magnitude counts of faint galaxies to appear artificially steep (cf. McGaugh 1994, Phillipps 1993). We find that, if we assume a ‘standard’ non-evolving galaxy population (essentially that used by Broadhurst, Ellis & Shanks 1988 amongst others) then isophotal effects alone cannot account for the discrepancy between the observed steepness and no-evolution models, though they could significantly reduce the amount of evolution required and alter the median redshifts. Modifying the underlying galaxy population by the addition of a bivariate brightness dwarf component as observed in clusters (e.g. Irwin et al 1990) increases the significance of the isophotal effects, though only fractionally, despite the fact that such effects would be highly important for such a population considered on its own.
Towards a Complete Library of Stellar Spectra for Evolutionary Synthesis
Authors: Cuisinier F. , Lejeune Th. , Buser R.
Published: July 2016

The population and evolutionary synthesis of the integrated light of clusters and galaxies requires a good knowledge of the underlying stellar spectra. Libraries of observed stellar spectra can be used, but they have several disadvantages, e.g. uneven sampling — which causes problems in the integration phase. Furthermore, no comprehensive library of low– or high–metallicity stars does exist, which would be required to model chemical evolution. Libraries of synthetic spectra could — and should — solve these problems. Using Kurucz and more recent libraries dedicated to cool stars, we constituted a library covering the whole range of Teff: 50 000 – 2500 K.
Bars in Cusps
Authors: Dehnen Walter
Published: July 2016

In order to investigate the stability properties of galaxy models with central density cusps, TV-body simulations of oblate models with density ρ ∝ m–1 (m+a)–3 where m2=R2+[z/q]2 and distribution functions f(E, Lz) (computed as in Dehnen, 1995) have been performed with the following results.

1.

An E7 model with identical amounts of stars of either sense of rotation was stable over 30 tdyn(r=a). This is interesting for the bending instability has been argued to set in at about this flattening and be responsible for the absence of flatter elliptical galaxies (Merritt & Sellwood, 1994).

2.

Rapidly rotating E≳E5 models quickly form weak bars inside the cusp, which are stronger for the more flattened, faster rotating initial configurations. The bars grow in a self similar fashion from inside out: the pattern speed decreases with increasing bar length and time. This process is initiated at the origin, where, because of finite AT, the actual density no longer follows the power law, and stops when the edge of the cusp is reached. A typical example is given in the figure showing the z-y-coordinates of particles with |z|<0.1a after ≃20tdyn(r=a) for an initially rapidly rotating E7-model. The bar has axis ratios of about 5:3:1, and extends almost to corotation. However, it has no sharp edge, but an inhomogenous density with a cusp steeper than the initial model. No sign of a buckling insta-bility has been observerd.
Colour (≈Age?) Gradients in Spiral Galaxies
Authors: de Jong Roelof S.
Published: July 2016

A sample of 86 galaxies was imaged in the B, V, R, I, H and K passbands to study their light and colour distribution as function of radius (de Jong & van der Kruit 1994). The radial colour gradients were compared with new dust models, which included both absorption and scattering, and with the stellar population synthesis models of Bruzual & Chariot (1993) and Worthey (1994). By requiring that the models had to fit all six passband photometry at the same time, the relative effects of dust, stellar age and stellar metallicity could be seperated (de Jong 1995a, 1995b). The main results from this investigation are:

–

All galaxies become bluer with increasing radius. The colour at each radius correlates strongly with the average surface brightness at that radius, with Hubble type being an additional effect. Late type galaxies are bluer at the same surface brightness than early type galaxies.

–

The reddening profiles predicted by the dust models are incompatible with the data when all colours have to be fitted at the same time. Dust cannot be the major cause of the colour gradients.

–

The population synthesis models by Worthey (1994) indicate that the colour gradients cannot be caused by metallicity gradients alone.

–

The best fit to the data is reached in a model where the colour gradients are mainly caused by an age gradient across the disk, with an additional metallicity gradient to explain the very red central colours. The colours of galaxies of type later than Sc indicate that they have in general a lower metallicity at all radii than the earlier types.
On the Dynamics of very Flattened Ellipticals
Authors: Dejonghe H. , de Bruyne V. , Vauterin P. , Zeilinger W.W.
Published: July 2016

Our aim is to study the generic phase-space structure of flattened ellipticals by investigating a few typical cases. Here we report on the E4 elliptical NGC 4697.

The construction of 2-integral and 3-integral distribution functions asks for photometry and kinematic data. In the course of the data analysis, we additionally detected a nuclear dust lane at 3.4″ or 0.4 kpc from the centre, which could be confirmed with HST data. This was put to good use to constrain the inclination.
The Ultraviolet Spectra of Old Stellar Populations
Authors: Dorman Ben , O'Connell Robert W.
Published: July 2016

We investigate the utility of UV spectra of old stellar populations as diagnostics of galaxy properties. For λ < 3800 Å, the integrated light of old stellar populations is dominated by two components: the hot stars which give rise to the UV upturn phenomenon at far-UV wavelengths, and the stars (i.e. main sequence, and subgiants) that lie closest to the turnoff. The mid-UV radiation from the turnoff varies strongly with metallicity, and less so with age; mid-UV light must be correct for the effect of the independent far-UV upturn component, but this is straightforward. Population synthesis models that account for the flux from the UV upturn can therefore determine the characteristics of the underlying stellar content from the mid-UV spectral region. The age & metallicity dependence of the far-UV 1550 Å is not well understood (see Dorman, O'Connell & Rood 1995, ApJ 442,105) since the mass loss mechanism on the RGB that produces very blue HB stars has no physical model. In contrast mid-UV indicators derive from the turnoff population which best represents the quantities we wish to measure, and are in addition visible at favourable optical wavelengths for z ≲ 1.
UV to NIR Galaxy Evolution and Galaxy Counts
Authors: Fioc Michel
Published: July 2016

We have improved in the NIR the model of galaxy evolution developed by Guiderdoni & Rocca-Volmerange (A&A 186, 1) in the UV and the visible, allowing thus a multispectral analysis of the evolution of galaxies and of faint galaxy counts. Since evolutionnary effects should be low in the near-infrared, cosmological ones might be put in evidence.
Dust VS. Color Gradients in Elliptical Galaxies
Authors: Goudfrooij Paul
Published: July 2016

Color gradients in elliptical galaxies are commonly interpreted as being due to stellar population gradients (e.g., Davies et al. 1993, MNRAS 262, 650). Here, I show that elliptical galaxies should generally contain a diffusely distributed component of dust, in addition to the “visible” component which is in the form of dust lanes or patches (see Fig. 1a). Employing a multiple scattering model for the dust, the presence of this newly postulated dust component is found to imply significant radial color gradients (see Fig. 1b). This should be taken seriously in the interpretation of color gradients in elliptical galaxies. This poster paper is based upon a (much!) more elaborate article by Goudfrooij & de Jong (1995, A&A 298, 784).
Constraints on Galaxy Evolution from Faint Redshift Surveys, Keck, and HST
Authors: Gronwall Caryl
Published: July 2016

The nature of faint field galaxy evolution remains controversial. While many workers advocate exotic theories, such as rapid merging or disappearing populations, we have found that it is possible to explain the published counts and redshift data with traditional luminosity evolution models which derive an optimal set of local luminosity functions for different galaxy types (Gronwall & Koo 1995). Recently, there has been a tremendous amount of new data addressing this question, including 1) the measurement of the galaxy luminosity function vs. redshift from faint redshift surveys down to B = 24 and I = 22 (Colless 1995; Lilly et al. 1995), 2) morphological and angular size data from the HST Medium Deep Survey (Driver et al. 1995; Phillips et al. 1995), and 3) redshift measurements with Keck for a small sample of galaxies with I > 22 (Koo 1995). We have explored these new data and have found that while our model continues to provide an excellent match to the faintest observed redshift and angular size distributions, it underpredicts the faint counts and luminosity function evolution for very blue late-type galaxies. Since our current model includes only minimal evolution of these galaxies, the new observations suggest a need for additional evolution, perhaps through a starbursting or mild merging component.
Anisotropy and Mass in Elliptical Galaxies
Authors: Jeske G. , Gerhard O.E. , Saglia R.P. , Bender R.
Published: July 2016

Changes in the anisotropy of the stars and changes in the galaxy potential due to dark matter manifest themselves differently in the observable line (velocity) profile shapes (VPs) of elliptical galaxies (Gerhard 1993, MNRAS 265, 213). In Fig. 1, this is illustrated for a set of realistic spherical models (Jeske et al. 1995, preprint).
Near-Infrared Spectroscopy of NGC 253: Starburst and Surroundings
Authors: Lutz D. , Prada F.
Published: July 2016

Near-infrared longslit spectra of NGC 253 obtained with IRSPEC at the ESO NTT are presented. By analysis of the 12CO 2.29μm bandhead we find that the stellar population in the central starburst region (r ∼ 150 pc) rotates more slowly than the gas, but has a velocity dispersion of 128 km/s, about twice the value found for emission lines from the gas in this region. This implies an about five times higher dynamical mass than previously derived (Rieke et al. 1980), removing the need to invoke a lower mass cutoff in the starburst initial mass function. The peak of near-infrared emission is displaced from the dynamical center.
Probing the Halo of Centaurus A: A Merger Dynamical Model for the PN Population
Authors: Mathieu A. , Dejonghe H. , Hui X.
Published: July 2016

We use planetary nebulae observations (Hui et al. 1995) to build dynamical models of the dust-lane elliptical galaxy NGC 5128 (Centaurus A). The PN photometric and kinematical data extend out to 20 kpc (∼ 4re) along the major axis and 10 kpc along the minor axis. Our models are built using a Quadratic Programming technique (Dejonghe 1989). The method produces fits to the data set, which consists of the photometry field (E2, well fitted by a r1/4-law) together with the major- and minor- axis rotation curves and velocity dispersion profiles. Assuming the merger hypothesis for Cen A, we describe its kinematics in a spherical potential by two sub-systems, one rotating about the intrinsic short axis and the other about the intrinsic long axis of the galaxy.
Anisotropic Distribution Functions for the Elliptical Galaxy NGC 1600
Authors: Matthias Michael , Gerhard Ortwin
Published: July 2016

Three-integral (3I) dynamical models for NGC 1600 were constructed as follows: (i) Lucy-inversion of CCD photometry and gravitational potential as in Binney, Davies, Illingworth (ApJ 361, 78, 1990), assuming axisymmetry. (ii) Third integral by perturbation theory as in Gerhard & Saha (MN 261, 311, 1991). (iii) Two- and three-integral distribution functions as in Dehnen & Gerhard (MN 261, 311, 1993), assuming various anisotropy patterns. The kinematic results from these models are presented in Fig. 1. The best-fitting 3I model (solid line, right panels) has outward-increasing radial anisotropy on the major axis and is nearly isotropic on the minor axis. The M/L of the various 3I-models varies only slightly around M/L=6.2.
Searching the Continuum for Primeval Galaxies
Authors: McCall Marshall L. , Derobertis Michael M.
Published: July 2016

A population of primeval galaxies (PG's) should be detectable by directly imaging with two intermediate-band filters tuned to either side of the Lyman break (DeRobertis, M. M., and McCall, M. L. 1995, A.J., 109, 1947). In the figure below, the solid and short-dashed curves show the flux (left scale) as a function of redshift from a PG 0.7 Gyr old with a total stellar mass of as seen through filters with rest-frame passbands 890 ± 30 Å (‘β’) and 1010 ± 30 Å (‘ρ’), respectively, moved to redshift 5. The upper curves depict the colour β – ρ (right scale); the dotted line is for the 0.7 Gyr population, and the dot-dashed line is for a 7.5 Gyr model. A source can be identified as a PG if it can be clearly detected in the ρ filter and if it has a colour greater than +0.75 mag. Confusion with any old stellar systems at lower redshifts can be eliminated by supplementing observations with Gunn r and i. The colour condition selects Lyman break objects between redshifts 4.7 and 5.4, a range over an order of magnitude greater than is achievable through an emission line survey. The discriminatory power of the technique is not affected by internal dust.
Properties of E & S0 Galaxies in the Coma Cluster
Authors: Mehlert Dörte , Bender Ralf , Saglia Roberto , Wegner Gary , Jørgensen Inger
Published: July 2016

As one of the richest nearby clusters, Coma is the ideal place to study the structure of galaxies as a function of environmental density, thus to constrain the theories of galaxy formation and evolution. For a magnitude limited sample of ≈ 40 E and S0 galaxies we want to obtain spectra with sufficient S/N and spatial resolution, that we can derive the rotation curves, the velocity dispersions profiles and the radial gradients of the line indices of Mg, Fe and Hβ. Following questions will be addressed:

•

Are the radial velocity dispersion profiles and the rotation of galaxies in high density environments similar to those in low density environments? Data for galaxies in low density environment are available from Bender et al. (1994, MNRAS, 269, 785). Are the centrally measured velocity dispersions representative for the mean kinetic energy of the galaxy?

•

Can the scatter in the Fundamental Plane (FP) - which tightly correlates the radii, surface brightnesses and (central) velocity dispersions (Djorgovski & Davis, 1987, ApJ, 313, 59; Dressier et al. 1987, ApJ, 313, 42) - for the Coma cluster be reduced if the mean kinetic energy is used instead of the central velocity dispersion? Can we derive stronger constraint on the variations in the M/L ratio than already implied by the FP?

•

The radial gradients of the line indices can be used to test the hypothesis that the metallicity gradient depends on the so-called “escape velocity” of the stars introduced by Franx & Illingworth (1990, ApJ, 359, L41). Also we can check whether the age of the stellar population varies with radius. Ages and metallicities can be estimated from the data with the use of stellar population models (Worthey 1994, ApJS, 95, 105; Bruzual & Chariot 1993, ApJ, 405, 538).

•

How does the radial variation of stellar populations and kinematics within the galaxies vary as a function of the clusters density profile?
The Central Bar in M 94
Authors: Möllenhoff C. , Matthias M. , Gerhard O.E.
Published: July 2016

Surface photometry in I, J, K of the oval disk galaxy M 94 (NGC 4736) reveal a weak central stellar bar of 0.7 kpc semi-major axis length, comprising ≈ 14% of the total light within 20″. By stellar kinematics the existence of a small spheroidal bulge with v/à ≈ 0.8 was discovered. The ionized gas (Hα) in this region shows global and local deviations from the stellar kinematics. Model calculations of closed orbits for the cold gas in the combined potential of bar, disk, and bulge predict large non-circular motions in equilibrium flow. However, these do not fit the observed gas kinematics; obviously hydrodynamical forces play a role in the central region of M 94.
Old Starbursts in Active Nuclei: The Connection between Starburst and Seyfert Activity
Authors: Origlia L. , Moorwood A.F.M. , Oliva E.
Published: July 2016

Infrared spectra of selected stellar absorption features (CO 2.29, 1.62 and Si 1.59 μm) of a sample of Seyferts and many calibrators (stellar clusters, normal galaxies and well known starbursters) are presented. For HII and Seyferts we also report Brγ measurements.
Multiple Gaseous Disks in NGC 1052
Authors: Plana H. , Boulesteix J.
Published: July 2016

We present detailed velocity field of NGC 1052 in [NII]6583Å line obtained with scanning Perot-Fabry. Extended ionized gas was studied by Davies et al. (1986) showing a clear counter-rotation between ionized gas and stars. It is an E4 galaxy type with ‘Boxy’ isophotes (Nieto et al. 1991). Taking benefit from high spectral resolution and 2D mapping of Scanning PF, we have discovered several components in our profiles (Plana 1995). Their study shows two main gaseous components: a first one with a Major Axis at PA=45° and a second one at PA=30°. The ionized gas extension is approximately 40″ for the first component and 20″ for the second. The main component contains 100 times more gas than the second one.
Galaxies and Photometric Signature of Starburst
Authors: Rakos K.D. , Maindl T.I. , Schombert J.M.
Published: July 2016

In a series of papers (see Rakos & Schombert 1995, ApJ 439, 47), we have carried out CCD photometry of galaxies in rich clusters at various redshifts. We use a modified Strömgren system, modified in the sense that the filter set is “redshifted” to the cluster of galaxies in consideration (i.e., λobs = λ(1 + z), therefore no k-correction). We call it uz, vz, bz, yz to distinguish it from the original zero redshift system.
Isolating Red Giants in M31's outer Spheroid: The Metallicity Gradient
Authors: Reitzel D. , Guhathakurta P. , Gould A.
Published: July 2016

The aim of our project is to measure the metallicity gradient in the spheroid of the Andromeda galaxy (M31). Deep KPNO 4-m UBRI images of a 15′ × 15′ field in the outer spheroid of M31 are being used to isolate a sample of red giant branch (RGB) stars. These stars are distinguished from the more numerous distant field galaxies on the basis of broadband colors and image morphology. The color technique uses UBRI photometry for isolating faint stars while rejecting 97% of the background galaxies (Gould et al. 1992). This yields a sample of candidate RGB stars in M31's spheroid, located about 20 kpc from its center (in projection). The shape of the M31 RGB will be compared to those of Galactic globular clusters spanning a wide range of (known) metallicities. The metallicity of the M31 outer spheroid will be derived by interpolation. Combined with the metallicity measurement at 8.6 kpc in M31's spheroid (Pritchet & van den Bergh 1988), our new measurement will permit determination of the metallicity gradient of M31. This quantity is important for understanding galactic evolution as it provides a means to distinguish between the dissipational collapse model (Larson 1974) and the accretion model (Searle & Zinn 1978).
The HI Halo of NGC 891
Authors: Swaters R.A. , Sancisi R. , van Der Hulst J.M.
Published: July 2016

NGC 891 is a spiral galaxy very similar to our Galaxy, almost perfectly edge-on (i ≃ 89°) and nearby (D = 9.5 Mpc). For these reasons it has become a key system for the study of the vertical distribution of the interstellar medium in a spiral disk.
The X-Ray Emitting Galaxy Group SHKH 360
Authors: Tiersch H. , Oleak H. , Stoll D. , Schwope A.D. , Neizvestny S. , Böhringer H. , Cordis L.
Published: July 2016

Shkh 360 has the characteristic signature of a strongly interacting group. Seven galaxies are embedded in a common extended halo and the isophotes indicate clear signs of alignment in B,V, and R. The parameters of the group as the red shift, z, the distance, d, the projected diameter, D, (basing on H = 55 km/s/Mpc), the virial radius, Rvir, the velocity dispersion, σv, the virial mass, the crossing time, τ, and the space density of galaxies, n, are given in the Table.
Nuclear Disks Embedded in Elliptical Galaxies
Authors: van den Bosch Frank C. , de Zeeuw Tim
Published: July 2016

The Hubble Space Telescope has discovered a number of ellipticals and S0's with small nuclear, stellar disks (eg. van den Bosch et al. 1994, AJ, 108, 1579). The kinematics of these disks may allow a derivation of the central mass density of the host galaxy, in much the same way as is possible with ionized gas disks (e.g. M87; Harms et al. 1994, ApJ, 435, L35). In order to understand the kinematic signatures of these disks, we have constructed two-integral, axisymmetric models of ellipticals with nuclear stellar disks. We use the method developed by Hunter & Qian (1993, MNRAS, 262, 401) to calculate f(E, Lz), from which we derive the velocity profiles (VPs). Depending on the choice of the odd part of the DF, one can construct a large variety of models including some with counter-rotating cores.
Molecular Hydrogen at z = 2.8108
Authors: Williger G.M. , Lanzetta K.M. , Carswell R.F. , Baldwin J.A.
Published: July 2016

The Lyman and Werner bands of H2 in interstellar gas provide information about gas temperature, density and the ultraviolet radiation field, and possibly about dust content. This is especially useful for high redshift QSO absorption systems, where usually the only data available arise from absorption lines. We present 25 – 50 km s−1 resolution data taken with the CTIO 4m telescope plus echelle spectrograph of the Lyα forest region of 0528–250, which has a damped Lyα absorption system at z = 2.81. Using a χ2 profile fitting routine (Lanzetta & Bowen 1992. ApJ, 391, 48), we find an H2 fraction of ∼ 10−2, an order of magnitude below that of Galactic diffuse interstellar clouds. This may be caused by some combination of a less efficient H2 formation rate or an increased H2 dissociation rate. Using the relative populations of the J″ = 0, 1 rotational levels, we derive a kinetic temperature of TK = 136 ± 16 K. The total velocity spread as traced by sensitive metal transitions is 250 km s−1, consistent with a highly inclined, rotating ensemble of clouds associated with a luminous spiral galaxy. A representative section of the spectrum is shown below, binned at roughly the Nyquist rate with the χ2 fit to H2 of the z = 2.8108 absorption system.
CO and the Multiphase ISM
Authors: Mckee Christopher F.
Published: July 2016

CO observations indicate that molecular clouds have a complex multiphase structure, and this is compared with the multiphase structure of the diffuse interstellar medium. The trace ionization within the molecular gas is governed primarily by UV photoionization. Magnetic fields contribute a significantly larger fraction of the pressure in molecular clouds than in the diffuse interstellar medium. Observations suggest that the total Alfvén Mach number, mAtot, of the turbulence in the diffuse ISM exceeds unity; Zeeman observations are consistent with mAtot ≲ 1 in molecular clouds, but more data are needed to verify this. Most molecular clouds are self-gravitating, and they can be modeled as multi-pressure polytropes with thermal, magnetic, and wave pressure. The pressure and density within self-gravitating clouds is regulated by the pressure in the surrounding diffuse ISM.
Magnetic Structure Responsible for Coronal Disturbances: Theory
Authors: Pneuman G. W.
Published: July 2016

Due to the strong coupling between the coronal material and magnetic fields, magnetic structures are probably intimately involved, either actively or passively, in virtually all coronal disturbances. The purpose of this paper is to put into perspective the various roles magnetic fields can play in both exciting and guiding these observed transient phenomena. A discussion of our present theoretical concepts relevant to this subject can be conveniently divided into four categories.

We begin by discussing our present understanding of how the gross magnetic structure of the corona is determined. Important considerations here are the tendency for the coronal field to seek its lowest energy state, the effect of convection on the field, and the influence of the solar wind. Secondly, we investigate magnetic structures which reside in elevated energy states (higher than the energy of an equivalent potential field) as well as disturbances which appear to be related to changes in these configurations. Thirdly, the role of the field in guiding coronal disturbances is considered. This is evident for bulk motions (sprays, surges, flare loops, green line events, etc.), wave motions (flare associated waves, Alfvén waves), as well as for individual particle phenomena. Lastly, a special class of magnetic structures which seem to be constantly associated with coronal activity are discussed. These are the magnetic discontinuities such as neutral sheets and current sheets. In this context, the magnetic neutral point and associated reconnection phenomena are considered.
Coronal Magnetic Field Structure Derived from Two-Frequency Radioheliograph Observations
Authors: Kai K. , Sheridan K. V.
Published: July 2016

(Solar Phys.). An exceptional variety of positions and polarizations was found for two type I storms and numerous sporadic bursts observed during 15 consecutive days with the Culgoora radio-heliograph at 80 and 160 MHz.
Multiple Hard X-Ray Bursts and Associated Emissions
Authors: Vorpahl J.
Published: July 2016

Multiple hard X-radiation, along with associated emission at optical and radio wavelengths, is discussed for three events in particular: December 13, 1970–1832 UT; December 12, 1970–1843 UT; June 28, 1970–2001 UT. Characteristics of these events as well as other multiple hard X-ray bursts observed by the author (e.g., Vorpahl, J.: Solar Phys.29, 447, 1973) are given at the end. Data originated from hard X-ray experiments on the OGO-5 (Kinsey Anderson) and OSO-5 (Ken Frost) satellites and were compared so that the effect of pulse pile-up in the OGO-5 data could be observed. The two December flares occurred in different active regions separated by about 100000 km yet both produced hard X-ray bursts with similar structure. This suggests that the two regions were joined by extended field lines with the acceleration mechanism somewhere in between. Although nothing was visible in Hα (such as surges or post flare ejections) that would indicate connecting field lines, higher coronal structures could explain the similarity in hard X-rays from two separate regions.
The Flash Phase of Solar Flares: Satellite Observations of Electrons
Authors: Lin R. P.
Published: July 2016

Satellite observations of solar electrons bearing on flare particle acceleration and the generation of radio and X-ray emission are reviewed. The observations support a two stage acceleration process for electrons, one stage commonly occurring at the flare flash phase and accelerating electrons up to ~ 100 keV, and a second stage occurring only in large proton flares and accelerating electrons up to relativistic energies. The location of the acceleration region appears to be no lower than the lower corona.

The accelerated non-relativistic electrons generate type III radio burst emission as they escape from the Sun. Direct spacecraft observations of the type III emission generated near 1 AU and the energetic electrons, provide quantitative information on the characteristics of the electrons exciting type III emission, the production of plasma waves, and the conversion from plasma waves to electromagnetic radiation.
Meter and Decameter Wavelength Positions of Solar Radio Bursts of July 31–August 7, 1972
Authors: Kundu M. R. , Erickson W. C.
Published: July 2016

(Solar Phys.). The positional analysis of solar bursts at meter and decameter wavelengths during the period July 31–August 7, 1972 is presented. The observations were taken with two arrays – a log periodic array of 16 elements situated on an E–W base line of 3.3 km and portions of the new Clark Lake array in the form of a Tee (an E–W arm of 32 log spiral antennas and a N–S arm of 16 similar antennas). The new array operates over the frequency range 10–120 MHz and has angular resolutions of approximately 3.′5 at 100 MHz and 8.′5 at 40 MHz in the E–W direction.
Source Structure in Metre-Wave Type V Solar Bursts
Authors: Labrum N. R. , Duncan R. A.
Published: July 2016

(Astrophys. Letters). The type V burst has been defined as a wideband continuum which sometimes appears for a minute or so following a type III burst (Wild et al., 1959b). It is now generally accepted that type III bursts arise from plasma waves set up by electrons escaping with velocity ~c/3 along open magnetic field lines (Wild et al., 1959a; Stewart, 1965); the most widely accepted explanation of type V continua is that they arise from plasma waves set up by electrons of similar velocity which have become trapped in a coronal magnetic loop (Weiss and Stewart, 1975). On this hypothesis the plasma waves are set up by two opposing electron streams in the trapping region, and from this consideration Zheleznyakov and Zaitsev (1968) have concluded that type V emission should be predominantly at the second harmonic of the local plasma frequency. In this paper we describe and discuss some two-dimensional observations of source positions of type III–V events which were obtained at 80 MHz on the Culgoora radioheliograph.
A Relationship Between the Brightness Temperatures for Type III Bursts
Authors: Melrose D. B.
Published: July 2016

(Solar Phys.). The widely accepted emission mechanisms for type III bursts involve at least two stages. The first stage is the generation of Langmuir waves by the inferred stream of electrons. Emission at the fundamental frequency arises when these waves are scattered by thermal ions. Emission at the second harmonic arises when two Langmuir waves coalesce; however, the coalescence is possible only after an intermediate stage in which the distribution of Langmuir waves evolves towards isotropy due to scattering by thermal ions.