bluuebunny/crossref_metadata_2025 huggingface dataset:
Triggered star formation in OB associations
Authors: Chen W. P. , Lee H. T. , Sanchawala K.
Published: April 2007

We present causal and positional evidence of triggered star formation in bright-rimmed clouds in OB associations, e.g., Ori OB1, and Lac OB1, by photoionization. The triggering process is seen also on a much larger scale in the Orion-Monoceros Complex by the Orion-Eridanus Superbubble. We also show how the positioning of young stellar groups surrounding the H II region associated with Trumpler 16 in Carina Nebula supports the triggering process of star formation by the collect-and-collapse scenario.
Molecular cloud turbulence and the star formation efficiency: enlarging the scope
Authors: Vázquez-Semadeni Enrique
Published: April 2007

We summarize recent numerical results on the control of the star formation efficiency (SFE), addressing the effects of turbulence and the magnetic field strength. In closed-box numerical simulations, the effect of the turbulent Mach number ${\cal M}_{\rm s}$ depends on whether the turbulence is driven or decaying: In driven regimes, increasing ${\cal M}_{\rm s}$ with all other parameters fixed decreases the SFE, while in decaying regimes the converse is true. The efficiencies in non-magnetic cases for realistic Mach numbers ${\cal M}_{\rm s}$ 10 are somewhat too high compared to observed values. Including the magnetic field can bring the SFE down to levels consistent with observations, but the intensity of the magnetic field necessary to accomplish this depends again on whether the turbulence is driven or decaying. In this kind of simulations, a lifetime of the molecular cloud (MC) needs to be assumed, being typically a few free-fall times. Further progress requires determining the true nature of the turbulence driving and the lifetimes of the clouds. Simulations of MC formation by large-scale compressions in the warm neutral medium (WNM) show that the generation of the clouds' initial turbulence is built into the accumulation process that forms them, and that the turbulence is driven for as long as accumulation process lasts, producing realistic velocity dispersions and also thermal pressures in excess of the mean WNM value. In simulations including self-gravity, but neglecting the magnetic field and stellar energy feedback, the clouds never reach an equilibrium state, but rather evolve secularly, increasing their mass and gravitational energy until they engage in generalized gravitational collapse. However, local collapse events begin midways through this process, and produce enough stellar objects to disperse the cloud or at least halt its collapse before the latter is completed. Simulations of this kind including the missing physical ingredients should contribute to a final resolution of the MC lifetime and the origin of the low SFE problems.
The global star formation law: from dense cores to extreme starbursts
Authors: Gao Yu
Published: April 2007

Active star formation (SF) is tightly related to the dense molecular gas in the giant molecular clouds' dense cores. Our HCN (measure of the dense molecular gas) survey in 65 galaxies (including 10 ultraluminous galaxies) reveals a tight linear correlation between HCN and IR (SF rate) luminosities, whereas the correlation between IR and CO (measure of the total molecular gas) luminosities is nonlinear. This suggests that the global SF rate depends more intimately upon the amount of dense molecular gas than the total molecular gas content. This linear relationship extends to both the dense cores in the Galaxy and the hyperluminous extreme starbursts at high-redshift. Therefore, the global SF law in dense gas appears to be linear all the way from dense cores to extreme starbursts, spanning over nine orders of magnitude in IR luminosity.
Galactic-scale star formation by gravitational instability
Authors: Low Mordecai-Mark Mac , Li Yuexing , Klessen Ralf S.
Published: April 2007

We present numerical experiments that demonstrate that the nonlinear development of the Toomre instability in disks of isothermal gas, stars, and dark matter reproduces the observed Schmidt Law for star formation. The rate of gas collapse depends exponentially on the (minimum) value of the Toomre parameter in the disk. We demonstrate that spurious fragmentation occurs in the absence of sufficient resolution in our SPH model. Our models also reproduce observed star formation thresholds in disk galaxies. We finally briefly discuss the application of our models to the study of globular cluster formation in merging galaxies.
Cloud formation from large-scale instabilities
Authors: Kim Woong-Tae
Published: April 2007

We discuss recent advances in cloud formation via gravitational instability under the action of self-gravity, magnetic fields, rotational shear, active stars, and/or stellar spiral arms. When shear is strong and the spiral arms are weak, applicable to flocculent galaxies at large, swing amplification exhibits nonlinear threshold behavior such that disks with a Toomre parameter Q < Qc experience gravitational runaway. For most realistic conditions, local models yield Qc ~ 1.4, similar to the observed star formation thresholds. When shear is weak, on the other hand, as in galactic central parts or inside spiral arms, magneto-Jeans instability is very powerful to form spiral-arm substructures including gaseous spurs and giant clouds. The wiggle and Parker instabilities proposed for cloud formation appear to be suppressed by strong non-steady motions inherent in vertically-extended spiral shocks, suggesting that gravitational instability is a primary candidate for cloud formation.
Turbulent structure and star formation in a stratified, supernova-driven, interstellar medium
Authors: Joung M. K. Ryan , Low Mordecai-Mark Mac
Published: April 2007

We report on a study of interstellar turbulence driven by both correlated and isolated supernova explosions. We use three-dimensional hydrodynamic models of a vertically stratified interstellar medium run with the adaptive mesh refinement code Flash at a maximum resolution of 2 pc, with a grid size of 0.5 × 0.5 × 10 kpc. Cold dense clouds form even in the absence of self-gravity due to the collective action of thermal instability and supersonic turbulence. Studying these clouds, we show that it can be misleading to predict physical properties such as the star formation rate or the stellar initial mass function using numerical simulations that do not include self-gravity of the gas. Even if all the gas in turbulently Jeans unstable regions in our simulation is assumed to collapse and form stars in local freefall times, the resulting total collapse rate is significantly lower than the value consistent with the input supernova rate. The amount of mass available for collapse depends on scale, suggesting a simple translation from the density PDF to the stellar IMF may be questionable. Even though the supernova-driven turbulence does produce compressed clouds, it also opposes global collapse. The net effect of supernova-driven turbulence is to inhibit star formation globally by decreasing the amount of mass unstable to gravitational collapse.
Cold H I in turbulent eddies and galactic spiral shocks
Authors: Gibson Steven J. , Taylor A. Russell , Stil Jeroen M. , Brunt Christopher M. , Kavars Dain W. , Dickey John M.
Published: April 2007

H I 21cm-line self-absorption (HISA) reveals the shape and distribution of cold atomic clouds in the Galactic disk. Many of these clouds lack corresponding CO emission, despite being colder than purely atomic gas in equilibrium models. HISA requires background line emission at the same velocity, hence mechanisms that can produce such backgrounds. Weak, small-scale, and widespread absorption is likely to arise from turbulent eddies, while strong, large-scale absorption appears organized in cloud complexes along spiral arm shocks. In the latter, the gas may be evolving from an atomic to a molecular state prior to star formation, which would account for the incomplete HISA-CO agreement.
Dense gas formation triggered by spiral density wave in M31
Authors: Tosaki T. , Shioya Y. , Kuno N. , Nakanishi K. , Hasegawa T. , Matsushita S. , Kohno K. , Miura R. , Tamura Y. , Okumura S. K. , Kawabe R.
Published: April 2007

We present the high-resolution 12CO(J = 1 − 0), 13CO(J = 1 − 0) and 12CO(J = 3 − 2) maps toward a GMA located on the southern arm region of M31 using Nobeyama 45 m and ASTE 10 m telescopes. The GMA consists of two velocity-components, i.e., red and blue. The blue component shows a strong and narrow peak, whereas the red one shows a weak and broad profile. The red component has a lower 12CO(J = 1 − 0)/13CO(J = 1 − 0) ratio (~ 5) than that of the blue one (~ 16), indicating that the red component is denser than the blue one. The red component could be the decelerated gas if we consider the galactic rotational velocity in this region. We suggest that the red component is “post shock” dense gas decelerated due to a spiral density wave. This could be observational evidence of dense molecular gas formation due to galactic shock by spiral density waves.

We also present results from on-going observations toward NGC 604, which is the supergiant HII region of M33, using Nobeyama 45 m and ASTE 10 m telescopes. The ratio of 12CO(J = 3 − 2) to 12CO(J = 1 − 0) ranges from 0.3 to 1.2 in NGC 604. The 12CO(J = 1 − 0) map shows the clumpy structure while 12CO(J = 3 − 2) shows a strong peak near to the central star cluster of NGC 604. The high ratio gas is distributed on the arc-like or shell-like structure along with Hα emission and HII region detected by radio continuum. These suggest that the dense gas formation and second generation star formation occur in the surrounding gas compressed by the stellar wind and/or supernova in central star cluster.
Triggered star formation in the Magellanic Clouds
Authors: Bekki Kenji
Published: April 2007

We discuss how tidal interaction between the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC), and the Galaxy triggers galaxy-wide star formation in the Clouds for the last ~0.2 Gyr based on our chemodynamical simulations on the Clouds. Our simulations demonstrate that the tidal interaction induces the formation of asymmetric spiral arms with high gas densities and consequently triggers star formation within the arms in the LMC. Star formation rate in the present LMC is significantly enhanced just above the eastern edge of the LMC's stellar bar owing to the tidal interaction. The location of the enhanced star formation is very similar to the observed location of 30 Doradus, which suggests that the formation of 30 Doradus is closely associated with the last Magellanic collision about 0.2 Gyr ago. The tidal interaction can dramatically compress gas initially within the outer part of the SMC so that new stars can be formed from the gas to become intergalactic young stars in the inter-Cloud region (e.g., the Magellanic Bridge). The metallicity distribution function of the newly formed stars in the Magellanic Bridge has a peak of [Fe/H] ~−0.8, which is significantly lower than the stellar metallicity of the SMC.
Turbulence, feedback, and slow star formation
Authors: Krumholz Mark R.
Published: April 2007

One of the outstanding puzzles about star formation is why it proceeds so slowly. Giant molecular clouds convert only a few percent of their gas into stars per free-fall time, and recent observations show that this low star formation rate is essentially constant over a range of scales from individual cluster-forming molecular clumps in the Milky Way to entire starburst galaxies. This striking result is perhaps the most basic fact that any theory of star formation must explain. I argue that a model in which star formation occurs in virialized structures at a rate regulated by supersonic turbulence can explain this observation. The turbulence in turn is driven by star formation feedback, which injects energy to offset radiation from isothermal shocks and keeps star-forming structures from wandering too far from virial balance. This model is able to reproduce observational results covering a wide range of scales, from the formation times of young clusters to the extragalactic IR-HCN correlation, and makes additional quantitative predictions that will be testable in the next few years.
Conference summary: triggered star formation in a turbulent ISM
Authors: Elmegreen Bruce G.
Published: April 2007

While the overall star formation rate in a galaxy appears to depend primarily on the gas mass and density, with the timescale for conversion of gas into stars given by the dynamical time, turbulence and explosions are still important for the process of star formation because they control the birth correlations in space and time. Most star formation appears triggered by some specific process, whether it is a galactic spiral shock, the expansion of a superbubble, the compression of a bright-rimmed globule, or some seemingly random compressive event in a supersonically turbulent flow. These processes give space and time sequences for star birth that are well observed. Many examples were given at this conference. Shocks are the link between large-scale but weak galactic processes and small-scale but strong final collapses. The rate limiting step is on the largest scale, where the dynamical time is slowest. Both gravitational instabilities and pressurized triggering seem to work on the same local dynamical time, making it difficult to tell that star formation is highly triggered when observing only galactic scales.
High supernova rate and enhanced star-formation triggered in M81-M82 encounter
Authors: Arbutina B. , Urošević D. , Vukotić B.
Published: April 2007

It is a general belief that the starburst activity of a nearby galaxy M82 was triggered in a close encounter with its massive companion M81, a few tens of million years ago. Despite the lack of supernovae observed, multiwavelength radio observations of M82 discovered a considerable number of compact supernova remnant candidates. We use these remnants to estimate the supernova rate (SNR) and the enhanced star-formation (SFR) rate in M82, and compare them with rates in normal galaxies.
An inventory of supershells in nearby galaxies: first results from THINGS
Authors: Bagetakos Ioannis , Brinks Elias , Walter Fabian , de Blok Erwin
Published: April 2007

The HI Nearby Galaxy Survey (THINGS), is a 21–cm HI line survey of a sample of 34 nearby (3–10 Mpc) galaxies (Walter et al. 2005). The observations were carried out with the VLA and have a velocity resolution of 5 km s−1 or better and an angular resolution of 7″ which at this distance range corresponds to a linear resolution of 100–300 pc. One of the primary goals of THINGS is to look at the fine–scale structure of the Interstellar Medium (ISM) and examine how it varies as a function of Hubble type, star formation rate, galaxy mass, metallicity, etc. We present one of the first science results from this project, an inventory of HI shells in the galaxies NGC 628, NGC 3184, and NGC 6946.
Fine–scale structure of the neutral ISM in M81
Authors: Bagetakos Ioannis , Brinks Elias , Walter Fabian , de Blok Erwin
Published: April 2007

We present an analysis of the fine–scale structure of the neutral ISM as traced via the 21-cm line of atomic hydrogen (HI) in the nearby galaxy M 81. The data show a stunning amount of detail in the form of 330 expanding shells and holes in the neutral ISM of M 81. A comparison with similar structures found in two other spirals and two dwarf galaxies (M 31, M 33, IC 2574 and Holmberg II) reveals that the ISM in M 81 shares a lot of similarities with the two spirals, whereas the structure of its ISM is different to that in dwarf galaxies. The sizes of the HI holes in M 81 range from 80 pc (close to the resolution limit) to 600 pc; the expansion velocities can reach 20 km s−1; estimated ages are 2.5 to 35 Myrs and the energies involved range from 1050 to 3.5 x 1052 ergs. The amount of neutral gas involved is of order 104 to 106 solar masses.
Sequential star formation in the Sh 254-258 molecular cloud: HHT maps of CO J=3-2 and 2-1 emission
Authors: Bieging J. H. , Peters W. L. , Vilaro B. Vila , Schlottman K. , Kulesa C.
Published: April 2007

The molecular cloud associated with the Sh 254-258 group of 5 small H II regions appears to be forming a (late)-OB association. We have mapped the associated molecular cloud in the J=2-1 line of the CO molecule over 0.75o × 1o, and the CO J=3-2 line toward the 2 main peaks, with the University of Arizona Heinrich Hertz Submm Telescope (HHT). We propose a scenario for sequential formation of the stars exciting the H II regions, triggered by the compression/heating of the molecular gas.
Star formation thresholds derived From THINGS
Authors: Bigiel F. , Walter F. , de Blok E. , Brinks E. , Madore B.
Published: April 2007

We present first results from THINGS (The HI Nearby Galaxy Survey), which consists of high quality HI maps obtained with the VLA of 34 galaxies across a wide range of galaxy parameters (Hubble type, mass/luminosity). We compare the distribution of HI to the UV emission in our sample galaxies. In particular we present radial profiles of the HI (tracing the neutral interstellar medium) and UV (mainly tracing regions of recent star formation) in our sample galaxies. The azimuthally averaged HI profiles are compared to the predicted critical density above which organized large-scale star formation is believed to start (this threshold is based on the Toomre-Q parameter, which in turn is a measure for local gravitational instability).
Intergalactic star formation around NGC 5291
Authors: Boquien Médéric , Duc Pierre-Alain , Braine Jonathan , Brinks Elias , Charmandaris Vassilis , Lisenfeld Ute
Published: April 2007

Numerous instances of intergalactic star forming regions have been recently reported (see Duc et al. in this proceedings book). They are fueled by gaseous material expelled from parent galaxies. One spectacular example is the HI ring-like structure around the interacting system NGC 5291 (Malphrus et al. 1997) which hosts numerous HII regions (Duc & Mirabel 1998). In order to study how star formation proceeds in this specific environment, we have combined ultraviolet (Galex), Hα, 8 μm (Spitzer) and HI (VLA B-array) images of this system.
Comparing the structure of three dark globules
Authors: Campeggio L. , Maiolo B. M. T. , Strafella F. , Elia D.
Published: April 2007

We present a comparative study of three dark globules CB52, CB107, and DC267.4-07.5. By means of an accurate photometry, near-IR two-colour diagrams were derived for the stellar backgrounds and used to determine the colour excesses of the reddened stars (Campeggio et al. 2004). By assuming a normal interstellar reddening law (Rieke & Lebofsky 1985), the visual extinction can be obtained as Av = 15.87 E(H–K).
A multifrequency study of the active star forming region NGC 6357
Authors: Cappa C. E. , Barbá R. H. , Arnal M. , Duronea N. , Lajús E. Fernández , Goss W. M. , Vasquez J.
Published: April 2007

To investigate the interaction of the massive stars with the gas and dust in the active star forming region NGC 6357, located in the Sagittarius spiral arm at a distance of 1.7-2.6 kpc (Massey et al. 2001), we analyzed the distribution of the neutral and ionized gas, and that of the dust, based on Hα, [OIII] and [SII] images obtained with the Curtis-Schmidt telescope at CTIO, radio continuum observations at 1.465 MHz obtained with the Very Large Array (NRAO) in the DnC configuration (synthesized beam = 38″), Hi data from the Parkes survey (angular resolution = 15′), CO(1-0) observations obtained with the Nanten radiotelescope at Las Campanas Observatory (angular resolution = 2.7′), and IR images in the four MSX bands (angular resolution = 18.3″).
Triggered massive star formation in the LMC HII complex N44
Authors: Chen C.-H. R. , Chu Y.-H. , Gruendl R. A. , Heitsch F.
Published: April 2007

We have used Spitzer IRAC and MIPS observations of N44 to identify young stellar objects (YSOs). Sixty YSO candidates with masses ≳4M are identified. We have compared the distribution of YSOs with those of the ionized gas, molecular clouds, and HI gas to study the properties of star formation.
The Parkes methanol multibeam survey
Authors: Cohen R. J. , Caswell J. L. , Brooks K. , Burton M. G. , Chrysostomou A. , Cox J. , Diamond P. J. , Ellingsen S. , Fuller G. A. , Gray M. D. , Green J. A. , Hoare M. G. , Masheder M. R. W. , McClure-Griffiths N. , Pestalozzi M. , Phillips C. , Thompson M. , Voronkov M. , Walsh A. , Ward-Thompson D. , Wong-McSweeney D. , Yates J. A.
Published: April 2007

A new 7-beam methanol multibeam receiver was successfully commissioned at Parkes Observatory in January 2006, and has begun surveying the Milky Way for newly forming massive stars, that are pinpointed by strong methanol maser emission at 6.7 GHz. The receiver was jointly constructed by Jodrell Bank Observatory and the Australia Telescope National Facility for use on the Parkes and Lovell Telescopes. The whole galactic plane is being surveyed within latitudes ±2°, with a velocity resolution of 0.1 km s−1 and a 5-σ sensitivity of ~0.7 Jy. Altogether 200 days of observing will be required.
The Mopra DQS survey of the G333 region
Authors: Cunningham M. R. , Bains I. , Lo N. , Wong T. , Burton M. G. , Jones P. A. ,   the DQS Team
Published: April 2007

Any successful model of star formation must be able to explain the low star forming efficiency of molecular clouds in our Galaxy. If the collapse of gas is regulated only by gravity, then the star formation rate should be orders of magnitude larger than the 1 M per year within our galaxy. The standard model invokes magnetic fields to slow down the rate of collapse, but does not explain star formation in cluster mode, or the lack of observed variations in the chemistry of molecular clouds if they are long-lived entities.
Studies of the Perseus Region.I.
Authors: Datta Srabani
Published: April 2007

Studies of molecular clouds have shown that they evolve from turbulent gas and dust to form coherent, dense and connected structures. We have conducted a multi-wavelength study of one such molecular cloud, the Perseus star-forming region, which includes Barnard 1 (B1), Barnard 3(B3), Barnard 5 (B5), NGC 1333, IC 348, L1455 and L1448. The data obtained using the Infrared Array Camera (IRAC), Multiple Imaging Photometer (MIPS), the Sub-mm Common User Bolometer Array(SCUBA) and the 2 Micron All Sky Survey (2MASS)provides information about the geometric structure of the dust and gas covering large areas around young stellar objects (YSO), dust temperatures, effect of turbulence and processes of molecule formation and their relevance in the chemical and physical evolution of the cloud. This paper presents our first results.
Evidence for triggered star formation in the Carina Flare supershell
Authors: Dawson Joanne , Kawamura A. , Mizuno N. , Onishi T. , Fukui Y.
Published: April 2007

Theory predicts the triggered formation of molecular clouds stars through the fragmentation and collapse of swept-up ambient gas. Yet the majority of Galactic HI shells show no more than a scattering of small molecular clouds. The Carina Flare supershell (Fukui et al. 1999) is a rare example of an HI shell with a striking molecular component. Here we present the large-scale morphology of the molecular and atomic gas and the location of YSO candidates. A detailed look at two molecular clumps in the shell walls reveals active, intermediate mass star forming regions at various stages of early evolution.
New insights into the nature of mid-infrared emission associated with massive star formation: disks and outflow
Authors: De Buizer James M.
Published: April 2007

Recent observations in the mid-infrared (5-25 μm) of massive young stellar sources have yielded a surprising result: many show evidence of mid-infrared emission from outflows and jets. These observations correlate well with other larger-scale outflow indicators and their geometries, such as what is seen in shock-excited H2 and CO emission. In some cases these mid-infrared observations identify the local maser emission as outflow or jet related.
From young massive star clusters to old globulars: long-term survival chances
Authors: de Grijs Richard
Published: April 2007

Young, massive star clusters (YMCs) are the most notable and significant end products of violent star-forming episodes triggered by galaxy collisions and close encounters. The question remains, however, whether or not at least a fraction of the compact YMCs seen in abundance in extragalactic starbursts, are potentially the progenitors of (≳10 Gyr) old globular cluster (GC)-type objects. If we could settle this issue convincingly, one way or the other, the implications of such a result would have far-reaching implications for a wide range of astrophysical questions, including our understanding of the process of galaxy formation and assembly, and the process and conditions required for star (cluster) formation. Because of the lack of a statistically significant sample of YMCs in the Local Group, however, we need to resort to either statistical arguments or to the painstaking approach of case-by-case studies of individual objects in more distant galaxies.
The virial balance of clumps and cores in molecular clouds
Authors: Dib Sami , Vázquez-Semadeni Enrique , Kim Jongsoo , Burkert Andreas , Shadmehri Mohsen
Published: April 2007

We study (i.e., Dib et al. 2006) the virial balance of clumps and cores (CCs) in a set of three-dimensional numerical simulations of driven, magnetohydrodynamical, isothermal molecular clouds (MCs). The simulations represent a range of magnetic field strengths in MCs from subcritical to non-magnetic regimes. We developed a clump-finding algorithm to identify CCs at different threshold levels in the simulation box, and for each object, we calculate all the terms that enter the virial theorem in its Eulerian form. We also calculate, other quantities commonly used to indicate the state of gravitational boundedness of CCs such as the Jeans number Jc, the mass-to magnetic flux ratio μc, and the virial parameter αvir. Our results suggest that a) CCs are dynamical out-of-equilibrium structures. b) The surface energies are of the same order than their volume counterparts and thus are very important in determining the exact energy balance in CCs. c) CCs can be either in the process of being compressed by the velocity field or of being dispersed. Yet, not all CCs that have a compressive velocity field at their boundaries are necessarily gravitationally bound. d) There is no one-to-one correspondence between the state of gravitational boundedness of a CC as described by the energy balance analysis (i.e., gravity versus other energies) or as implied by the classical indicators Jc, μc, and αvir. In general, from the energy analysis, we observe that only the inner regions of the objects (i.e., the dense cores selected at high threshold levels) are gravitationally bound, whereas Jc and αvir estimates tend to show that they are more gravitationally bound at the lowest threshold levels. g) We observe, in the non-magnetic simulation, the existence of a bound core with structural and dynamical properties that resemble those of the Bok globule Barnard 68 (B68). This suggests that B68 like cores can form in a larger molecular cloud and then be confined by the warm gas of a newly formed HII region, which can heat and rarefy the gas around the core, confine it, and extend its lifetime.
MHD simulations of supernova driven ISM turbulence
Authors: Gressel Oliver , Ziegler Udo
Published: April 2007

Large-scale magnetic fields, that can be observed in numerous galaxies, are most likely the outcome of a dynamic process, a so-called dynamo. The favoured mechanisms for driving such a process in the ISM are supernovae (SNe) and/or magneto-rotational instability (MRI). In this work we simulate the dynamic evolution of the turbulent ISM utilising a three-dimensional MHD model.
Bright knots along spiral arms in disk galaxies
Authors: Grosbøl P. , Dottori H.
Published: April 2007

Many spiral galaxies show bright knots along their arms on high resolution K-band images. Spectroscopy of such knots suggests that they are very young stellar clusters which formation was triggered by a large-scale front associated to a density wave. We have studied a sample of around 80 disk galaxies (with i < 65°) for which deep K-band maps with a resolution of <1″ are available and present preliminary statistics of such bright knots.
Young stellar clusters triggered by a density wave in NGC 2997
Authors: Grosbøl P. , Dottori H. , Gredel R.
Published: April 2007

Bright knots along the arms of grand-design spiral galaxies are frequently seen on near-infrared K-band images. To investigate their nature, low resolution K-band spectra of a string of knots in the southern arm of the grand design, spiral galaxy NGC 2997 were obtained with ISAAC/VLT. Most of the knots show strong Brγ emission while some have H2 and HeI emission. A few knots show indications of CO absorption. Their spectra and absolute K magnitudes exceeding -12 mag suggest them to be very compact, young stellar clusters with masses up to 5 × 104 M. The knots' azimuthal distance from the K-band spiral correlates well with their Brγ strength, indicating that they are located inside the co-rotation of the density wave, which triggered them through a large-scale, star-forming front. These relative azimuthal distances suggest an age spread of more than 1.6 Myr, which is incompatible with standard models for an instantaneous star burst. This indicates a more complex star-formation history, such as several bursts or continuous formation.
A method for detecting preferred scale sizes
Authors: Gustafsson Maiken , Lemaire Jean-Louis , Field David
Published: April 2007

Molecular clouds are usually thought to be dominated by turbulence where the structures are inherently self-similar and lack characteristic scale. However self-similarity must break down at scales associated with star formation which imposes a characteristic scale. The turbulence may be driven by energy injection at some larger scale which also imposes characteristic scale. In order to understand the evolution of molecular clouds it is important to identify the departures from self-similarity associated with the scales of self-gravity and the driving of turbulence.

We describe a method based on structure functions for determining whether a region of gas, such as a molecular cloud, is fractal or contains structure with characteristic scale sizes (Gustafsson, Lemaire & Field 2006). Using artificial data containing structure it is shown that derivatives of higher order structure functions provide a powerful way to detect the presence of characteristic scales should any be present and to estimate the size of such structures. The method is easy to implement and compared with other techniques such as Fourier transform or histogram techniques (Blitz & Williams), the method appears both more sensitive to characteristic scales and easier to interpret.

The method is applied to observations of hot H2 in the Kleinman-Low nebula, north of the Trapezium stars in the Orion Molecular Cloud, including both brightness and velocity data (Gustafsson, Kristensen, Clénet, et al. 2003). It is found that the density structure, represented by H2 emission brightness in the K-band (2-2.5μm), exhibits mean characteristic sizes of 110, 550, 1700 and 2700 AU. The velocity data show the presence of structure at 140, 1500 and 3500 AU. These scales are respectively disk scales (140 AU) and outflow scales (>1000 AU), the latter being associated with (re-)injection of energy.
HST emission line images of the Orion HII region: proper motions and possible variability
Authors: Gutiérrez Leonel , Giammanco Corrado , Beckman John E.
Published: April 2007

Using HST emission line images of the Orion Nebula, separated by 7 years in epoch, we have obtained evidence of localized temporal variability of both density and temperature during this period. Applying a digital filter to reduce high frequency noise, we used images in Hα and [OIII] to quantify separately the variability in these two parameters. We detected fractional temperature variations of order 0.4% on scales of 2′10−2 pc. The same images yielded proper motion information; using cross-correlation to optimize the accuracy of the differential measurements we produced velocity field maps across the nebula, with vectors ranging up to ~130kms−1 across the line of sight. It is notable that in zones of rapid proper motion we find by far the largest density variations, as would be expected. It is much easier to quantify the temperature variations, on the other hand, in zones with low or zero detectable proper motion (see the other figure here), though these temperature variations appear across the whole face of the nebula.
The high latitude low mass star forming region Cometary Globule 12: two compact cores and a C18O hot spot
Authors: Haikala L. K. , Juvela M. , Harju J. , Lehtinen K. , Mattila K. , Olberg M. , Dumke M.
Published: April 2007

Cometary globule CG 12 lies at the distance of 630 pc more than 200 pc above the Galactic plane. The cloud's structure could be due to the passage of a supernova blast wave. Curiously, the cometary tail points at the galactic plane which would put the putative supernova even farther above the Galactic plane than the globule. The globule contains a low/intermediate mass stellar cluster with at least 9 members (Williams et al. 1977). The head of CG 12 has been observed using NIR imaging (NTT SOFI), mm continuum (SEST SIMBA) and sub mm (APEX) and mm (SEST) spectroscopy (Haikala & Olberg 2006, Haikala et al.). The molecular material is distributed in a North-South 10' long elongated lane with two compact maxima separated by 3'. Strong C18O (3-2), (2-1) and (1-0) emission is detected in both maxima and both have an associated compact 1.2 mm continuum source. The Northern core, CG 12 N, is cold and is possibly still pre-stellar. A dense and compact core is observed in DCO+ and CS emission in the direction of the Southern core, CG 12 S. A remarkable C18O hot spot was detected in CG 12 S. This is the first detection of such a compact, warm object in a low mass star forming region. The hot spot can be modelled with a 60″ to 80″ diameter (~0.2 pc) hot (80 K ≲ Tex≲ 100 K) 1.6 solar mass clump (Haikala et al. 2006). The hot spot lies at the edge of a dense cloud core and on the axis of a highly collimated bipolar molecular outflow (White 1993). The driving source of the outflow is most probably embedded in the dense core. NIR imaging reveals a bright cone like feature with a faint counter cone in the centre of CG 12 S. The size of the CG 12 compact head, 1.1 pc by 1.8 pc, and the C18O mass larger than 100 solar masses are comparable to those of other nearby low/intermediate mass star formation regions.
Diffuse X-ray emission from the Carina Nebula observed with Suzaku
Authors: Hamaguchi K. , Petre R. ,   the Suzaku η Carina team
Published: April 2007

The Carina Nebula possesses the brightest soft diffuse X-ray emission among the Galactic giant HII regions, but the origin has not been known yet. The XIS1 back-illuminated CCD camera onboard the Suzaku X-ray observatory has the best spectral resolution for extended soft sources so far, and is therefore capable of measuring these key emission lines in the soft diffuse plasma. Suzaku observed the Carina nebula on 2005 Aug. 29. The XIS1 spectra of the Carina nebula clearly showed spatial variations in emission line strengths. In the south, the spectrum showed strong L-shell lines of iron ions and K-shell lines of silicon ions, while in the north these lines were much weaker. Fitting the spectra with an absorbed thin-thermal plasma model with kT ~ 0.2, 0.6 keV and NH ~ −2 × 1021 cm−2 showed that the silicon and iron abundance is about 2–3 times higher in the south than in the north. Because of its large size (~40 pc), the diffuse emission in the Carina nebula might have been produced by an old supernova, or a super shell produced by multiple supernovae.
Discovery of large-scale masers in W3(OH)
Authors: Harvey-Smith L. , Cohen R. J.
Published: April 2007

We report a vast filament of hydroxyl and methanol maser emission surrounding the ultra-compact HII region W3(OH). The filament stretches 3100 AU and has a linear velocity gradient. By studying the velocity structure, line profiles and extended methanol maser structures we believe we have located the position of the central star and detected around it a circumstellar disc with a large velocity gradient of 47 km s−1 arcsec−1.
IRSF/SIRIUS near-infrared survey of the Magellanic Clouds: triggered star formation in N11 in the Large Magellanic Cloud
Authors: Hatano H. , Kadowaki R. , Kato D. , Sato S. ,   the IRSF/SIRIUS group
Published: April 2007

A near-infrared survey of the Magellanic Clouds has been carried out with IRSF/SIRIUS. As a part of the results, we present a study of triggered star formation in N11 in the LMC.
A (Sub)Millimeter survey of massive star-forming regions identified by the ISOPHOT Serendipity Survey (ISOSS)
Authors: Hennemann Martin , Birkmann Stephan M. , Krause Oliver , Lemke Dietrich
Published: April 2007

A sample of potential massive starforming regions identified at 170 m by ISO was observed in the submillimeter and millimeter regime. These observations allow us to infer physical properties of the molecular cloud cores. Two sources are presented in detail: ISOSS J23053+5953 and J183640221 show viable candidates for massive protocluster cores. Our analysis shows very low temperatures and low levels of turbulence of the major mass fraction in the molecular cloud cores besides active star formation at an early evolutionary stage. These conditions seem similar to the low mass case and may precede phases of luminous infrared emission observed towards young massive protostars.
Non-symmetrical protoplanetary disks destroyed by UV photoevaporation
Authors: Hetem A. , Gregorio-Hetem J.
Published: April 2007

We have developed geometric disk models to study the circumstellar geometries by fitting the spectral energy distribution (SED) of T Tauri and Herbig Ae/Be stars. The simulations provide means to recognize the signatures of different disk structures, including the effects due to external UV photoevaporation.

Following Chiang & Goldreich (1997) and Dullemond et al. (2001), we used hydrostatic, radiative equilibrium models for passive, reprocessing flared disks. The grains in the surface of the disk are directly exposed to the radiation from the star and the interior of the disk is heated by diffusion from the surface. Adopting this two-layers disk structure, our disk model was improved in order to optimize the parameters estimated by using a calculation technique based on genetic algorithms presented by Bentley & Corne (2002).

In the present work, we apply the code to model the SED of protoplanetary disks, which have being destroyed by photoevaporation due to the presence of ionizing OB stars, as the example of Trapezium region in the Orion Nebula. We compare geometric disk characteristics and physical conditions evaluated by our method to those obtained to the “proplyds” studied by Scally & Clarke (2001), Robberto et al. (2002) and Smith et al. (2005), among others. We also conclude that the parameter estimation by genetic algorithms assures accurate and efficient calculations.
ASTE Submillimeter observations of a YSO condensation in Cederblad 110
Authors: Hiramatsu Masaaki , Kamegai Kazuhisa , Hayakawa Takahiro , Tatematsu Ken'ichi , Onishi Toshikazu , Mizuno Akira , Hasegawa Tetsuo
Published: April 2007

Outflow-cloud interaction is an important issue in discussions about star formation in clusters because it could generate turbulence and restrain star formation activities, as well as it causes outflow-triggered star formation.
Giant Molecular Associations in M51
Authors: Hitschfeld M. , Kramer C. , Schuster K. , Garcia-Burillo S. , Stutzki J.
Published: April 2007

We present a 12CO 2-1 map of M51 (Schuster et al. 2006) at 11″ resolution observed with HERA at the IRAM-30m telescope. The map covers the companion galaxy NGC5195 as well as the south-western arm out to 12 kpc. Using the IRAM-30m data and the clump finding procedure GAUSSCLUMPS (Stutzki et al. 1990), we obtain the masses, positions, peak temperatures and more intrinsic properties as i.e. deconvolved sizes of Giant Molecular Associations (GMAs) in M51 (Hitschfeld et al. 2007, in prep.).
Galaxy open clusters and associations: study of stellar population
Authors: Hojaev Alisher S.
Published: April 2007

Some results of Galaxy star clusters and associations observation are presented.
Turbulence in the G333 molecular cloud
Authors: Jones P. A. , Cunningham M. R. , Bains I. , Muller E. , Wong T. , Burton M. G. ,   the DQS Team
Published: April 2007

We are studying the molecular clouds in the region around G333.6-0.2 in a number of 3-mm transitions from different molecular species, to probe, among other things, the turbulent properties. The observations are being made by on-the-fly mapping with the 22-m diameter single-dish Mopra radio telescope. See Bains et al. (2006) and Cunningham et al. (2006 in these proceedings) for more details. During 2004 and 2005 we obtained 13 CO (1 – 0), C18O, CS (2 – 1) and C34S data. Using the different molecular tracers gives complementary information about the gas density structure, due to the different critical densities, and different isotopomers allows correction for optical depth effects.
High-resolution mapping of interstellar clouds with near-infrared scattered light
Authors: Juvela M. , Pelkonen V.-M. , Padoan P. , Mattila K.
Published: April 2007

We examine the intensity of scattered near-infrared (NIR) light in the case of interstellar clouds illuminated by the normal interstellar radiation field. We have developed a way to convert the observed surface brightness into estimates of the column density and have estimated the accuracy of the new method. The NIR intensities can be converted into reliable estimates of the column density in regions with AV up to almost 20 magnitudes. The errors can be further reduced with detailed radiative transfer modelling and by using the lower resolution information that is provided by the colour excess data of background stars. Therefore, NIR scattered light is a promising new way to map quiescent interstellar clouds at a high, even sub-arcsecond resolution.
The distribution of early-type stars in the Mon-CMa-Pup-Vel region of the Milky Way
Authors: Kaltcheva N. T.
Published: April 2007

An overall uvby β photometric survey of the structure of the star-forming fields located toward the Monoceros-Canis Major-Puppis-Vela region of the Milky Way is presented.
Submillimeter-wave observations of outflow and envelope around the low mass protostar IRAS 13036-7644
Authors: Kamegai Kazuhisa , Hiramatsu Masaaki , Hayakawa Takahiro , Tatematsu Ken'ichi , Hasegawa Tetsuo , Onishi Toshikazu , Mizuno Akira
Published: April 2007

The interaction between molecular outflow from a protostar and ambient molecular cloud would play an important role in dissipating circumstellar envelope, changing chemical composition, and triggering next generation star formation. In order to investigate the interaction in submillimeter wavelength, we have made line observations toward the low mass protostar IRAS 13036-7644 (Class 0/I) in the Cha II dark cloud. Although millimeter observations found CO outflow and evidence of mass infall toward the protostar (e.g. Lehtinen 1997), no submillimeter observation has been reported so far.
3D Spectroscopy of the Blue Compact Dwarf Galaxies IZw18 and IIZw70
Authors: Kehrig C. , Vílchez J. M. , Sanchez S. F. , Lopez-Martin L. , Telles E. , Martin-Gordón D.
Published: April 2007

Blue compact dwarf (BCD) galaxies are low-metallicity objects undergoing violent star formation (Searle & Sargent 1972). We present our ongoing work on integral field spectroscopy (IFS) of the two prototypical BCD galaxies IIZw70 and IZw18 (Papaderos et al. 2002). Two-dimensional spectroscopy allows us to collect simultaneously the spectra of many different regions of an extended object, combining photometry and spectroscopy in the same data set. The great advantage of using IFS for the investigation of galaxies is that it allows us to obtain data on the galaxies' positions, velocity fields and star-forming properties all in one data cube. The observations were taken with the instruments INTEGRAL/WYFFOS at the WHT (ORM, La Palma) and PMAS installed on the 3.5m telescope at the CAHA, covering a spectral range from λ 3600 to 6800 Å. The data are mainly used to study the ionized gas and stellar clusters. Our main goal is to investigate the presence of spatial variations in ionization structure indicators, physical conditions and gaseous metal abundances, in these galaxies (Vílchez & Iglesias-Páramo 1998). We also study the kinematical properties of the ionized gas, as well as systematic variations of ionization structure and physical-chemical parameters as a function of the surface-brightness in Hα emission. Maps of the relevant emission lines are presented.
HI clouds in the Large Magellanic Cloud
Authors: Kim S.
Published: April 2007

We discuss the results of HI survey of the LMC and a catalog of HI clouds.
ASTE observations of dense molecular gas in galaxies
Authors: Kohno K. , Muraoka K. , Nakanishi K. , Tosaki T. , Kuno N. , Miura R. , Sawada T. , Sorai K. , Okuda T. , Kamegai K. , Tanaka K. , Endo A. , Hatsukade B. , Ezawa H. , Sakamoto S. , Cortes J. , Yamaguchi N. , Matsuo H. , Kawabe R.
Published: April 2007

Atacama Submillimeter Telescope Experiment (ASTE) is a joint project between Japan and Chile for installing and operating a 10 m high precision telescope in the Atacama Desert in order to explore the southern sky through the submillimeter wavelength. We have achieved an accuracy of 19 μm (rms) for the main reflector surface and a stable radio pointing accuracy of about 2 arcsec (rms). A 350 GHz cartridge type SIS mixer receiver achieves good performance with a typical system noise temperature of 150 ~ 250 K in DSB and a main beam efficiency of 0.6 ~ 0.7 during winter nights.

A large scale CO(3-2) imaging survey of nearby galaxies using ASTE is now in progress. One of our goals is to compare our wide area CO(3-2) images with existing CO(1-0) data as well as distributions of massive star formation tracers (i.e., Hα and radio continuum emission) in order to understand the physical mechanism which controls the global star formation properties such as star formation efficiency. Initial CO(3-2) maps of some sample galaxies (M 83, NGC 604 in M 33, NGC 1672, & NGC 7130) are reported.
Three-dimensional MHD simulations of magnetized molecular cloud fragmentation with turbulence and ion-neutral friction
Authors: Kudoh T. , Basu S.
Published: April 2007

We perform a 3D-MHD simulation of a self-gravitating isothermal gas layer that is initially penetrated by a uniform magnetic field. The strength of the initial magnetic field is such that the cloud is slightly subcritical. In this system, we input random supersonic turbulence initially. Ion-neutral friction is also introduced in the magnetized gas so that the magnetic diffusion allows gas to go across the magnetic field and form self-gravitating cores. We found that self-gravitating cores are formed in the dense region enhanced by the shock waves if ion-neutral friction is introduced. The time scale of core formation is on the order of the 106 years, which is faster than the usual magnetic diffusion time (107 years) estimated from the initial condition. Our result is consistent with the results of 2D-MHD simulations by Li & Nakamura (2004).