bluuebunny/crossref_metadata_2025 huggingface dataset:
The Different Environmental Dependencies and Evolutions of Giant and Dwarf Galaxies
Authors: Haines C.P. , Gargiulo A. , Mercurio A. , Merluzzi P. , La Barbera F. , Busarello G. , Capaccioli M.
Published: April 2007

The star-formation histories, masses and structural properties of galaxies are strongly dependent on their environment: massive, passively-evolving spheroids dominate cluster cores, while in field regions, galaxies are typically low-mass, star-forming and disk-dominated (e.g Blanton et al. 2005). Equally the global properties of galaxies have been found to be bimodally distributed around a stellar mass of ~3 × 1010 M⊙ (~M*+1) (e.g. Kauffmann et al. 2003). Large-scale spectroscopic surveys have shown that the evolution of massive galaxies is primarily driven by their merger history, rather than through direct interection with the cluster environment, as demonstrated by the finding of massive passively-evolving galaxies in all environments, mild observed environmental trends for their mean stellar ages, and the gradual SF-density relation in which star-formation is still seen to be suppressed in galaxies 3–4 virial radii from the nearest cluster. In contrast, in the dwarf regime (>M*+2) dramatic changes are seen in both the luminosity function and red galaxy fraction between those galaxies in the cores of clusters and those at the virial radius (Mercurio et al. 2006, Haines et al. 2006a).

We have examined the origins of the bimodality observed in the global properties of galaxies by comparing the environmental dependencies of star-formation for giant and dwarf galaxy populations. Using SDSS DR4 spectroscopic data to create a volume-limited sample complete to M*+3, we find that the environmental dependences of giant and dwarf galaxies are quite different, implying fundamental differences in their evolution (Haines et al. 2006b). Whereas the star-formation histories of giant galaxies are determined primarily by their merger history, this is not the case for dwarf galaxies. In particular, we find that old or passive dwarf galaxies are ONLY found as satellites within massive halos (clusters, groups or giant galaxies), with none in the lowest density regions. This implies that star-formation in dwarf galaxies must be much more resilient to the effects of mergers, and that the evolution of dwarf galaxies is primarily driven by the mass of their host halo, through effects such as suffocation, ram-pressure stripping or galaxy harassment.
X-ray Morphology of Clusters of Galaxies and its Application
Authors: Hashimoto Y. , Boehringer H. , Henry J. P. , Hasinger G. , Szokoly G.
Published: April 2007

We report our study of X-ray cluster morphology using a sample of 101 clusters of galaxies at redshift z~0.05-1 taken from the Chandra archive.
Extremely Red Galaxies in Abell 1835
Authors: Hempel A. , Schaerer D. , Richard J. , Egami E. , Pelló R.
Published: April 2007

We use multi-colour data of the gravitational lensing cluster Abell 1835 to search for high-z candidates (Richard et al. 2006) and extremely red galaxies.

Applying a colour criteria of R-K ≥ 5.6 we have selected 12 EROs, of which 10(9) have no R(I)-band detection. Two of these sources posses multiple detections in the ACS z850 band, possibly gravitationally bound objects.

Using the method of Pozzetti and Mannucci (2000) to classify an ERO either as evolved elliptical or dusty starburst, we find that two thirds of all objects have colours assigned to evolved ellipticals. One of the remaining 4 sources is the known sub-mm source SMMJ14009+0252.

The spectral energy distributions of sources with no optical detection show strong similarities to the SED of the high-z object of Mobasher et al. (2005), i.e. a degeneracy between a low- and high-z solution. However, for objects we accept the low-z solution as the better fit.

A detailed analyses of the colour properties and spectral energy distribution will be published in two forthcoming papers (Schaerer et al., Hempel et al.).
Nature of X-ray Sources From the Field of Nearby, Poor Cluster of Galaxies
Authors: Hudaverdi M. , Kunieda H. , Ercan E.N.
Published: April 2007

A194 and A1060 are studied for the nature of point source properties. X-ray to optical luminosity ratios (Lx/Lb) are evaluated for selected galaxies. Cumulative log(N)-log(S) and intrinsic luminosity functions are applied for a comparative evaluation with Lockman Hole. 46 and 32 X-ray point sources are detected by EPIC-PN, for A194 and A1060 respectively. The XLF space density shows significant excess compared to field and local group space density. The result is interpreted as the fueling of AGNs as they enter the ICM from outskirts of the clusters and dimming of the very bright AGNs as they further proceed into cluster core.
The Structure and Interaction History of Moderate Luminosity Mergers
Authors: Hüttemeister Susanne , Manthey Eva
Published: April 2007

Interaction and merging are the two most important driving forces of galaxy evolution. In contrast to the well studied major mergers of two large gas-rich disk galaxies, which may lead to Ultraluminous Infrared Galaxies (ULIRGs, LFIR>1012 L⊙), mergers between galaxies of unequal mass or a spiral and an elliptical (S+E mergers) are still poorly understood. These moderate luminosity mergers typically have LFIR > 1011 L⊙. Here, we present the results of our multiwavelength study of a sample of such kind of mergers, including interferometric HI and single-dish CO observations, optical and near-infrared imaging as well as optical spectroscopy.
New Kinematics for the Central Spheroid in Polar Disk Galaxy NGC4650A
Authors: Iodice E. , Arnaboldi M. , Saglia R. , Sparke L. , Gerhard O.
Published: April 2007

We have obtained high angular resolution spectra on the photometric axes of the stellar spheroid in the polar disk galaxy NGC4650A. We discuss the main implications by the new kinematics on the previous mass models for NGC4650A and on current formation scenarios of Polar Ring Galaxies (PRGs).
The Kelvin-Helmholtz Instability in Smoothed-Particle Hydrodynamics
Authors: Junk Veronika , Heitsch Fabian , Naab Thorsten
Published: April 2007

Smoothed Particle Hydrodynamics (SPH) simulations are a powerful tool to investigate hydrodynamical processes in astrophysics such as the formation of galactic disks. Dense gas clouds raining on the forming disk are possibly disrupted by Kelvin-Helmholtz-Instabilities (KHI). To understand the evolution of the halo clouds, we have to ascertain the capability of SPH to treat the KHI correctly, since SPH-methods tend to suffer from an innate surface tension and viscosity effects, both of which could dampen the KHI. We analytically derive a growth rate of the KHI including surface tension and viscosity in the linear regime, and compare this growth rate to results of numerical simulations by an SPH method and a grid-based method. We find that SPH in some cases suppresses the KHI (Junk et al., in prep).
Mid- and Far-Infrared Study of X-ray-emitting Dusty Elliptical Galaxies
Authors: Kaneda H. , Onaka T. , Kitayama T. , Okada Y. , Sakon I.
Published: April 2007

We study nearby X-ray-emitting dusty elliptical galaxies in mid- and far-infrared by using the Spitzer Space Telescope and AKARI, the Japanese infrared astronomical satellite.
Metal Enrichment Processes in the ICM – Starbursts and Galactic Winds
Authors: Kapferer W. , Kronberger T. , Domainko W. , Schindler S. , van Kampen E. , Kimeswenger S. , Ruffert M. , Mair M. , Breitschwerdt D.
Published: April 2007

We present an investigation of the metal enrichment of the intra-cluster medium (ICM) by galactic winds and merger-driven starbursts. We use combined N-body/hydrodynamic simulations with a semi-numerical galaxy formation model. The inhomogeneities in the metal distribution caused by these processes are an ideal tool to reveal the dynamical state of a galaxy cluster. We show that X-ray weighted metal maps distinguish between pre- or post-merger galaxy clusters by comparing the metallicity distribution with the galaxy-density distribution: pre-mergers have a metallicity gap between the subclusters, post-mergers a high metallicity between subclusters.
Surface photometry of cD envelopes
Authors: Kemp S. N. , Jiménez V. Guzmán , Beraud P. Ramírez , Ibarra F. J. Hernández , Grana J. A. Pérez
Published: April 2007

We have carried out deep BVR surface photometry of 6 cD and cD-like galaxies using the 2.1-m telescope at San Pedro Mártir, cD galaxies are supergiant galaxies (M>1013M⊙) with enormous halos (>100 kpc in radius) surrounding a giant elliptical galaxy, found generally at the centre of rich clusters (Oemler 1976, Schombert 1988). The surface brightness profiles of their halos (envelopes) break from the r1/4 law, containing more light at large radii (Schombert (1988)), although a detailed 1 and 2 dimensional analysis of their morphology has yet to be carried out. There have been four main theories as to the origin of cD envelopes (Schombert (1988) and references within), a) stripping of stars from other cluster member galaxies, b) formation of galaxy and envelope at the same time during the formation of the cluster, c) mergers of cluster members, which do not easily explain the high velocity dispersions in the envelopes (~ 1000 km s−1), d) cooling flows: accumulation of cooling X-ray-emitting ICM gas around the central galaxy. Very red envelopes have been found around some cD's, and star formation biased towards lowmass stars in cooling flows were invoked to explain these red halos, but the expected very bright near-IR halos were not detected (Joy et al. 1995 and references within). Previous detailed studies of cD galaxies (e.g. Mackie 1992) found a range of colour gradients.
Fossil Galaxy Groups; Scaling Relations, Galaxy Properties and Formation of BCGs
Authors: Khosroshahi Habib G. , Ponman T. J.
Published: April 2007

We study fossil galaxy groups, their hot gas and the galaxy properties. Fossils are more X-ray luminous than non-fossil groups, however, they fall comfortably on the conventional L-T relation of galaxy groups and clusters indicating that their X-ray luminosity and temperature are both boosted, arguably, as a result of their early formation. The central dominant galaxy in fossils have optical luminosity comparable to the brightest cluster galaxies (BCGs), however, the isophotal shapes of the central galaxy in fossils are non-boxy in contrast to the isophotes of majority of the BCGs.
Internal Kinematics of Modelled Isolated and Interacting Disc Galaxies
Authors: Kronberger T. , Kapferer W. , Schindler S. , Böhm A. , Kutdemir E. , Ziegler B. L.
Published: April 2007

We present a systematic investigation of the velocity fields of both isolated and interacting spiral galaxies in combined N-body/hydrodynamical simulations. Closely mimicking the procedures applied in observations of distant, small, and faint galaxies we extract rotation curves (RCs) and compare the results of the simulation directly to observations. Irregularities in the velocity field reflect disturbances in the gravitational potential of the galaxy. They can be used to trace the recent interaction history of a galaxy and give possible clues to the type of the respective interaction. In addition, identifying disturbances in the RCs is important for Tully-Fisher studies in order to accurately derive the maximum rotation velocity.
The Far-Infrared Properties of the Most Isolated Galaxies
Authors: Lisenfeld U. , Verdes-Montenegro L. , Sulentic J. , Leon S. , Espada D. , Bergond G. , García E. , Sabater J. , Santander-Vela J. D. , Verley S.
Published: April 2007

We describe the mid- (MIR) and far- (FIR) infrared properties of a large (~1000) sample of the most isolated galaxies in the local Universe. This sample is intended as a “nurture-free” zero point against which more environmentally influenced samples can be compared. We reprocess IRAS MIR/FIR survey data using the ADDSCAN/SCANPI utility for 1030 out of 1050 galaxies from the Catalogue of Isolated Galaxies (CIG) as part of the AMIGA project. We focus on diagnostics (FIR luminosity LFIR, R = log(LFIR/LB) and IRAS colours) thought to be sensitive to effects of environment or interaction. The distribution of log(LFIR) is sharply peaked from 9.0–10.5 with very few (<2%) galaxies above 10.5. Review of available optical images of the most FIR luminous galaxies finds the majority to be, likely, interacting systems missed in our earlier morphological reevaluation. The optically normalised luminosity diagnostic R = log(LFIR/LB) shows a distribution sharply peaked between 0.0 and −1.0. These results were compared to the magnitude limited CfA sample that was selected without environmental discrimination. This modestly (e.g. compared to cluster, binary galaxy and compact group samples) environmentally affected sample shows significantly higher mean log(LFIR) and R, whereas the mean log(LB) is the same. Our sample shows a strong LFIR vs. LB correlation, with a slope steeper than one (LFIR ∝ L1.41B). Interacting galaxies were found above this correlation, showing an enhancement in LFIR. With respect to the IRAS colours, we found higher F60/F100 value for ellipticals and late-type galaxies than for spirals, indicating a higher dust temperature. The mean value of F60/F100 was found to be lower than for interacting samples from the literature. The results indicate that the FIR emission is a variable enhanced by interaction, and that our sample probably shows the lowest possible mean value. This attests to the utility of our sample for defining a nurture-free zero point. More details can be found in the paper (The AMIGA sample of isolated galaxies, III. IRAS data and infrared diagnositics, U. Lisenfeld et al.) which is accepted for publication in Astronomy & Astrophysics.
The Evolution of Galaxies and Groups in Cluster Environments at 0.3 < z < 0.6
Authors: Li I. H. , Yee H. K. C. , Hsieh B. C. , Gilbank D. G. , Gladders M. D.
Published: April 2007

We investigate the dependence of galaxy populations on environment. Our samples are selected from the follow-up of Red-Sequence Cluster Survey (RCS) catalogs using wide-field BVRz' imaging for 60 intermediate redshift (0.3 < z < 0.6) clusters. Galaxy redshifts are estimated using an empirical photometric redshift technique with a training set of 3996 galaxies to z 1.4. To obtain photometric redshift probability density for each galaxy, we bootstrap the training set galaxies to estimate the fitting uncertainties and apply Monte-Carlo method to simulate galaxy magnitudes errors. In order to find galaxy groups using photometric redshift, we develop a modified friends-of-friends algorithm, ‘Probability Friends-of-Friends Algorithm (pFOF)’, where photometric redshift redshift probability densities of individual galaxies are used to determine member galaxies of a group. We calculate the red galaxy fraction to infer the evolutionary status of cluster galaxies and also for galaxies in groups selected in the same redshift space as the clusters.
Nuclear Activity in UZC Compact Groups
Authors: Martinez M. A. , del Olmo A. , Focardi P. , Perea J.
Published: April 2007

We have analyzed the level and type of nuclear activity in 720 galaxies belonging to a large complete sample of Compact Groups (UZC-CGs). We have found that most (67%) galaxies show emission lines and that the most frequent (43%) nuclear activity is AGN. AGNs are mainly hosted in bright early type galaxies and early spirals, at variance with HII which reside in late spirals of lower luminosity. CGs which have a dominant content of AGNs and TOs have larger σv and lower Rp than CGs dominated by HII.
Galaxy Transformations in Different Environments of the Shapley Supercluster
Authors: Mercurio A. , Merluzzi P. , Haines C. P. , Gargiulo A. , Busarello G. , La Barbera F. , Capaccioli M.
Published: April 2007

We studied ~ 2 deg2 region in the Shapley Supercluster (SSC) core at z~0.05 in two bands (B and R). By studying the galaxy luminosity function (LF) and the colour distribution of galaxies we find that processes directly related to the supercluster environment are responsible for transforming faint galaxies, rather than galaxy merging.
Galaxy Evolution Traced by Multiple Galaxies from the BIG Sample
Authors: Mickaelian Areg M.
Published: April 2007

Optical identifications of all IRAS PSC sources at high galactic latitudes by means of the First Byurakan Survey (FBS) in the area with +61° < δ < +90° at galactic latitudes |b|>15° have been carried out with a total surface of 1487 deg2. 1577 sources have been optically identified, 1178 sources corresponding to galaxies. The BIG sample (Byurakan-IRAS Galaxies) was constructed of 1178 newly identified galaxies and 789 other IRAS galaxies in the same area, known before, altogether 1967 galaxies. Studies of the BIG objects include: spectroscopic follow-up for the brighter (<18m) objects; discovery and study of new AGN; discovery and study of new ULIRGs; deep imagery of the most interesting objects and the “empty fields”; 2D spectroscopy of interacting/merging systems; search for obscured IRAS galaxies (with the Spitzer Space Telescope), etc. The BIG objects are a rich source for new AGN, high-luminosity IR galaxies (hence, starburst activity), and interacting/merging systems. All these phenomena are crucial for understanding the galaxy evolution and their interrelation, as well as the triggering of the powerful IR radiation. In frame of the redshift survey of these galaxies, spectroscopic observations have been carried out for the BIG objects (including the pairs and multiples) by means of the Byurakan Astrophysical Observatory (BAO, Armenia) 2.6m, Special Astrophysical Observatory (SAO, Russia) 6m, and Observatoire de Haute Provence (OHP, France) 1.93m telescopes. It is shown that, without an exception, all double/multiple BIG systems are physical pairs or groups, and they are mostly interacting and/or merging systems. From the high IR luminosities derived from the observations, one can conclude that perhaps the ULIRG/HLIRG phenomenon is connected with galaxy interactions/merging. We find an evolution in luminosity function of these objects with respect to their redshift distribution.

Existence of AGN among the multiple BIG objects provides a chance for study of the galaxy evolution in sense of interrelationship between the three phenomena: starburst, interactions/merging, and nuclear activity. We have shown (Mickaelian et al. 2001) that the maximum IR luminosity of a single spiral galaxy may not be larger than 1012 Solar luminosities. Hence, all high-L IRAS galaxies are interacting pairs/multiples or mergers. But what is the relation of the active nucleus to the starburst (i.e. IR) activity?
The Early-Type Dwarf Galaxy Population of the Fornax Cluster
Authors: Mieske Steffen
Published: April 2007

AIMS: We analyse the photometric properties of the early-type Fornax cluster dwarf galaxy population (MV> − 17 mag), based on a wide field imaging study of the central cluster area in V and I bandpasses. We used the instrument/telescope combination IMACS/Magellan at Las Campanas Observatory, providing much larger light collecting area and better image resolution than previous wide field imaging surveys.

METHODS: We create a fiducial sample of Fornax cluster dwarf ellipticals (dEs) in the following three steps: (1) To verify cluster membership, we measured I-band surface brightness fluctuations (SBF) distances to candidate dEs known from previous surveys; (2) We re-assessed morphological classifications for those candidate dEs that are too faint for SBF detection; and (3) We searched for new candidate dEs in the size-luminosity regime close to the resolution limit of previous surveys.

RESULTS: (1) We confirm cluster membership for 28 candidate dEs in the range −16.6 < MV < −10.1 mag by means of SBF measurement. We find no SBF background galaxy. (2) Of 51 further candidate dEs in the range −13.2 < MV < −8.6 mag, 2/3 are confirmed as probable cluster members by morphological re-assessment, while 1/3 are re-classified as probable background objects. (3) We find 12 new dE candidates in the range −12.3 < MV < −8.8 mag, two of which are directly confirmed via SBF measurement. The resulting fiducial dE sample follows a well-defined surface brightness – magnitude relation, showing that Fornax dEs are about 40% larger than Local Group dEs. The sample also defines a colour-magnitude relation that appears slightly shallower than that of Local Group dEs. The early-type dwarf galaxy luminosity function in Fornax has a very flat faint end slope α ≃ −1.1 ± 0.1. We discuss these findings in the context of structure formation theories.

CONCLUSIONS: The SBF method is a very powerful tool to help constrain the faint end of the galaxy luminosity function in nearby galaxy clusters. For the Fornax cluster, morphological cluster memberships – if performed at sufficient resolution – are very reliable.

This contribution is based on Mieske et al. (2006).
The Arecibo Galaxy Environments Survey–Description of the Survey and Early Results
Authors: Minchin R. F. , Auld R. , Davies J. I. , Catinella B. , Cortese L. , Linder S. , Momjian E. , Muller E. , O'Neil K. , Rosenberg J. , Sabatini S. , Schneider S. E. , Stage M. , van Driel W. ,   the AGES team
Published: April 2007

The Arecibo Galaxy Environments Survey (AGES) is a 2000-hour neutral hydrogen (H I) survey using the new Arecibo L-band Feed Array (ALFA) multibeam instrument at Arecibo Observatory. It will cover 200 square degrees of sky, sampling a range of environments from the Local Void through to the Virgo Cluster with higher sensitivity, spatial resolution and velocity resolution than previous neutral hydrogen surveys.
Poor Groups Around Strong Gravitational Lenses
Authors: Momcheva Ivelina , Williams Kurtis , Zabludoff Ann , Keeton Charles
Published: April 2007

Poor groups are common and interactive environments for galaxies, and thus are important laboratories for studying galaxy evolution. Unfortunately, little is known about groups at z ≥ 0.1, because of the difficulty in identifying them in the first place. Here we present results from our ongoing survey of the environments of strong gravitational lenses, in which we have so far discovered six distant (z ≥ 0.5) groups of galaxies. As in the local Universe, the highest velocity dispersion groups contain a brightest member spatially coincident with the group centroid, whereas lower-dispersion groups tend to have an offset brightest group galaxy. This suggests that higher-dispersion groups are more dynamically relaxed than lower-dispersion groups and that at least some evolved groups exist by z ~ 0.5. We also compare the galaxy and hot gas kinematics with those of similarly distant clusters and of nearby groups.
Multi-passband search for galaxy clusters in CFHTLS D1
Authors: Olsen L. F. , Benoist C. , Mazure A. , Adami C.
Published: April 2007

We compare the results of applying different cluster detection methods to photometric data obtained for the Deep-1 field of the Canada-France-Hawaii Telescope Legacy Survey. The poster can be downloaded at http://www.dark-cosmology.dk/~lisbeth/cfhtls_clusters.pdf
The Baryonic Matter at Supercluster Scales: The Case of Corona Borealis Supercluster
Authors: Padilla-Torres Carmen P. , Rebolo Rafael , Gutiérrez Carlos M. , Watson Robert , Génova-Santos Ricardo , Juncosa Robert
Published: April 2007

Superclusters of galaxies are the largest gravitationally bound structures of the Universe. Numerical simulations indicate that a significant fraction of baryonic matter could be located in supercluster (SC) scales in the form of a warm/hot plasma. The sensitivity and resolution of the VSA interferometer at Teide observatory allow us to search for evidence of the Sunyaev-Zeldovich effect (SZE). We have published evidence for such a plasma towards the center of the Corona Borealis Supercluster (CrB-SC), Génova-Santos et al. (2005). Two large decrements in the intensity of the signal measured by VSA at 33 GHz (CrB-B and H) subtending an angle of about 25' could be indicative of a concentration of baryonic matter comparable to thousands of galaxies. This matter could be in the form of a plasma of temperature ~105 − 107 K where no clusters of galaxies have been identified. No other similar spots have been found in the VSA fields observed to measure the CMB primordial power spectrum of fluctuations, Rubiño-Martin et al. (2003), and suggests that this is indeed a very particular feature of the CrB-SC of galaxies. Additional data obtained with the MITO telescope of CrB-H also support this VSA finding Battistelli et al. (2006), and could be related to warm/hot plasma in the SC. We would expect a galaxy population to be associated with such a plasma, as it is well known to occur in clusters of galaxies where the SZE has been measured, Lancaster et al. (2005). However, the absence of X-ray emission in the ROSAT images in the CrB-SC SZ spots suggests that if there is a galaxy population linked to the plasma it may have a peculiar spatial distribution. We obtained photometry of CrB-SC region using the data base from SDSS DR4, covering a total of 15o2 in the CrB-SC area. We built a catogue with 121251 galaxies down a selection criterion based on galaxies colours 0.2 ≤ r − i ≤ 0.6 and δ(g, r, i) ≤ |0.2| errors. In order to study the behaviour of differents regions in the CrB-SC, four regions were measured that belongs it, two regions not associated with overdensity, A2065, and CrB-H with 30' radius for each ones. The completeness magnitude is R ≤ 21. A photometric study produced colour-magnitude diagrams where we can detect evidence that many of these galaxies belong to the same system. The excess in the number density of galaxies appears to be larger in CrB-H where the strongest CMB temperature decrement was found. The number of galaxies in it is a factor ~1.5 lower than A2065 and ~2.5 highest that the SC background field. This resembles the typical number of galaxies in clusters of galaxies. However, it appears these galaxies are more broadly distributed than in the well known clusters of this SC. It is possible that the hot plasma causing the SZ spot is indeed associated with a new large concentration of galaxies unidentified in the SC.
SFR Relation with Galaxy Environment and Colour at z between 0.03 and 0.1
Authors: Premadi Premana W. , Maryam A. Sitti
Published: April 2007

This work is a preliminary result of our attempt to examine the use of SFR in the study of galaxy evolution. For this purpose we use the Sloan Digital Sky Survey Data Release 2 (SDSS DR2) Abazajian et al. (2004) and the SFR Catalogue generated from this data set by Brinchmann et al. (2004) and Kaufmann et al. (2003). Following Kewley et al. (2001) we use the Diagnostic Diagram, log ([OIII]/Hβ) vs log ([NII]/Hα), to separate the star forming galaxies from other emission lines sources such as AGN. Choosing only those with S/N > 3 out of the Brinchmann et al. (2004) catalogue, we arrive at about 200 thousand galaxies as our starting SFR subsample. With 0.05 < z < 0.22 and limit at r = 17.77, the subsample can be used to reconstruct the properties of a volume limited sample of galaxies with M* = 6 1010Modot. We benefit from the fact that Brinchmann et al. (2004) SFR Catalogue has already been aperture-corrected using the likelihood distribution P(SFR/Li/colour) scheme. For the environment, we use the data generated by Kaufmann et al. (2003), and arrive at about 40 thousand target galaxies. In this work the environment is characterised by the number (N=0-30) of neighbouring galaxies within a projected radius of 2 Mpc and velocity di.erence of 500km/s from each target galaxy, and the magnitude limit is 14.5 < r < 17.77.
Interactions in Barred Galaxies: Effects of a Companion on the Bar Pattern Speed
Authors: Puerari Ivânio , Pfenniger Daniel
Published: April 2007

We study the effects of a companion in a parabolic co-planar orbit on the bar pattern speed. Unlike previous simulations, we use fully self-consistent 3D N-body simulations with live haloes, which are known to be important for bar evolution.
Near Infrared Photometry of Southern Pairs and Triplets of Galaxies
Authors: Puerari Ivânio , Valdez-Gutiérrez Margarita , Gurovich Sebastian , Freeman Kenneth F. , Hernández-Toledo Héctor
Published: April 2007

We present near infrared photometry of select pairs and triplets of galaxies observed with the CASPIR camera attached to the 2.3m Advanced Technology Telescope at Siding Spring Observatory, Australia. The preliminary results show that galaxies in pairs or triplets present near infrared colors that are redder than normal galaxies. We also performed a morphological analysis using bi-dimensional Fourier Transform techniques, as well as classical bulge + disk fits. Compared to isolated galaxies, the light distribution of galaxies in pairs and triplets often needs a larger number of Fourier coefficients to be well represented. Also, light profiles usually show deviations from the exponential disk (disk distortions, strong bars, etc.). In the future we intend to define some method to quantify the strength of the interactions by using the Fourier coefficients and/or the magnitude of the deviations from the classical Sersic + exponential laws.
Retarded Evolution of Low-Mass Galaxies in Voids?
Authors: Pustilnik S. A. , Kniazev A. Y.
Published: April 2007

We analyze possible differences in the global environments of very metal-poor BCGs with that of typical metallicity BCGs, basing on the parameter DNN – distance to the nearest “luminous” galaxy. We find very significant difference suggesting that a higher fraction of unevolved dwarfs reside in ‘voids’.
Caught in the Act: Witnessing a~Transforming Spiral in a Galaxy Group
Authors: Rasmussen J. , Ponman T. J. , Mulchaey J. S.
Published: April 2007

Ram pressure stripping of galaxies is believed to be inefficient in galaxy groups, but Chandra X-ray observations of the starburst spiral NGC 2276, a member of a small galaxy group, shows that this galaxy is being stripped of its gas at a rate of ~5 M⊙ yr−1 due to its motion through hot intragroup gas. This provides direct evidence that mechanisms associated with ram pressure can strip galaxies of their gas in systems much smaller than galaxy clusters.
The Formation of Young Clusters in Three Ongoing Galaxy Mergers
Authors: Rothberg B. , Whitmore B. , Schweizer F. , Chandar R. , van der Marel R. , Rossa J. , Blair W. , Mengel S. , Rieke M.
Published: April 2007

High-resolution, multi-wavelength (UV through NIR) imaging from the Hubble Space Telescope has been obtained for three mergers in the Toomre Sequence, NGC 520, NGC 2623, & NGC 3256, to identify and measure the properties of young Globular Cluster (GC) candidates. Unlike previous merger studies, this work focuses on objects that lie in the middle of the Toomre Sequence. This age range represents a critical dynamical transition in the merging sequence between ongoing mergers and advanced remnants with properties more akin to elliptical galaxies. The early results of our investigation include luminosity functions and age-dating of the GC candidates. These results also address the impact of the dynamical state of the merger on the current young cluster population as compared with earlier studies that have dealt with the very oldest and very youngest mergers in the Toomre Sequence.
The Effect of Galaxy Mergers in the Local Galaxy Population
Authors: Sampson Leda , Trentham Neil
Published: April 2007

The luminosity function (LF) is one of the most fundamental quantities to be observed in Astronomy. It is determined by the combined effects of the various physical phenomena that drive galaxy formation and evolution, therefore it is a very useful tool to constrain cosmological models.
Galaxy properties from voids to clusters in the SDSS-DR4
Authors: Sorrentino G. , Rifatto A. , Antonuccio-Delogu V.
Published: April 2007

We investigate the environmental dependence of galaxy populations properties in the SDSS-DR4. Our aim is to search for systematic variations in the properties of galaxies with the local galaxy density in order to find hints that can be related to the presence of a void galaxy population. We find that galaxies in underdense regions (voids) are fainte and bluer than cluster galaxies. Moreover, the transition from underdense to overdense regions is smooth, as well as the percentage of late-type galaxies decreases while the percentage of early-type galaxies increases smoothly from underdense to dense environments.
Galaxy Interactions and Their Cosmic and Morphological Evolution
Authors: Chatterjee Tapan K.
Published: April 2007

Merger theory, in its extreme form, postulates that ellipticals are the products of mergers of spirals. While the morphology-clustercentric relationship (Whitmoreet al., 1993), indicates that the morphological fractions are unaffected by the local properties of the clusters, considerable observational evidence has surfaced in favor of the existence of marginally bound pairs; that are the source of the most frequent collisions (Chengaluret al., 1996 and references therein). To test the global impact of galaxy collisions on their evolution we have studied many collisions between spirals and ellipticals, as well as spiral and elliptical pairs. The details of the models and methods are in Chatterjee & Magalinsky, 2002; and we refer to it. Marginally bound, eccentric orbits are found to maintain their eccentricities for a long time; which is supported by analytical research (Magalinsky & Chatterjee, 2000). The calculation of collision frequency indicates that only of the order of 5% of ellipticals can be formed in this way. A remarkable phenomenon is that the fraction of blue galaxies around z = 0.3 to 0.5 is more than in the present epoch – the B-O effect (Butcher & Oemler, 1978). While observations indicate that the effect is primarily due to an increase in galaxies with perturbed morphology (e.g., Faberet al., 1995), in the same environment we find a homogeneous population of normal red galaxies, that have almost finished their star formation.
Results From VLA Observations of Five Spiral Galaxies In The Virgo Cluster Region
Authors: Toribio M. C. , Solanes J. M.
Published: April 2007

New HI synthesis observations have been made for the five spiral galaxies NGC 4307, NGC 4356, NGC 4411a/b and NGC 4492, located in the Virgo Cluster Region, with the Very Large Array in its CS configuration. All these objects, but NGC 4411a, belong to a sample of spirals identified in previous single-dish studies of the HI distribution within the Virgo Cluster and its outskirts. The thirteen members of that sample were selected for showing neutral gas deficiencies as strong as those of the inner galaxies of Virgo and other rich clusters, but apparently lying on the infall region.

The goal of the present observations is to progress further on the identification of the external mechanisms that may be responsible for the reduction of the interstellar gas in spiral galaxies and thus contribute to the study of the evolution of galaxies in high-density environments. In particular, the results of this work are relevant for the ongoing debate on the pre-processing of galaxies prior to entering the cluster environment.
Galaxy Population in the Infall Regions of Intermediate Redshift Clusters
Authors: Verdugo Miguel , Ziegler Bodo L.
Published: April 2007

We investigate the galaxy populations in 6 clusters of different x-ray luminosities at intermediate redshifts (z ≈ 0.25) concentrating on their star formation activity. Our ~500 Calar Alto MOSCA spectra come from targets covering large fields out to 2–4 cluster virial radii. To probe this so-called infall region is important since here newly arriving galaxies from the surrounding field encounter the special environment of clusters for the first time. We selected 3 fields containing 2 clusters each from the X-ray Dark Cluster Survey (Gilbank et al. 2004). Results for one field were already published by Gerken et al. 2004.

We find evidence that the process(es) that suppresses or truncates the star formation activity in cluster galaxies, sets in already at rather large distances from the cluster cores corresponding to low projected local galaxy densities. This changes the fraction of star forming galaxies rather quickly.
Chandra and XMM Observations of Galaxy Groups: The Influence of Central AGN at the Low End of the Cluster Mass Scale
Authors: Vrtilek J. M. , O'Sullivan E. J. , David L. P.
Published: April 2007

Chandra and XMM, offering between them high angular resolution, substantial collecting area, and spatially-resolved spectroscopy at good spectral resolution, have given us the means to discover hitherto unanticipated phenomena, in groups as in clusters, and to explore a new set of issues that bring us closer to understanding the formation and evolution of groups and their constituent galaxies: the distribution of heavy elements, the presence of X-ray cavities and their relation to radio observations, the nature of cooling cores, and X-ray signatures of recent galaxy interactions. We here show Chandra and XMM data selected to illustrate recent results regarding some of these themes.
The Faint-End of the Galaxy Luminosity Function in the Hydra I Cluster
Authors: Yamanoi H. , Tanaka M. ,   Suprime-Cam Group
Published: April 2007

We examine the galaxy luminosity functions (LFs) in the Hydra I cluster (Abell 1060) at z = 0.0126, for which very faint galaxies (down to M ~ −10) have not been surveyed yet. We conclude that the total LF has a slightly steep slope (α ~ −1.6) at −20 < M < −10 in the B- and RC-bands. The numbers of galaxies at the faint end (M ≳ −14) differ in between the cluster center and the outskirts slightly. We divide the Hydra member galaxies into red/blue galaxies and find that the shape of LFs in the faint magnitude range is determined by red dwarf galaxies.
Star – Gas Cycle in Galaxies
Authors: Palouš Jan
Published: April 2007

The importance of the star-gas cycle for the evolution of galaxies is discussed. We describe three different ways of stellar mass loss: a) the gas return from low and intermediate mass stars, b) the stellar winds from OB associations; c) the superwinds from superstar clusters.
Simulations of Cosmic Chemical Enrichment
Authors: Kobayashi Chiaki
Published: April 2007

We simulate cosmic chemical enrichment with a hydrodynamical model including supernova and hypernova feedback. We find that the majority of stars in present-day massive galaxies formed in much smaller galaxies at high redshifts, despite their late assembly times. The hypernova feedback drives galactic outflows efficiently in low mass galaxies, and these winds eject heavy elements into the intergalactic medium. The ejected baryon fraction is larger for less massive galaxies, correlates well with stellar metallicity. The observed mass-metallicity relation is well reproduced as a result of the mass-dependent galactic winds.
Neutral Gas and Metals From z = 4 to z = 0.5
Authors: Péroux Céline
Published: April 2007

A complementary method to the emission selection of high-redshift galaxies consists in the observation of absorbers along the line of sight toward a background quasar. This selection technique has a constant sensitivity at all redshifts up to z = 6 (i.e. no redshift desert) and allow to select all types of galaxies regardless of their luminosity or star formation rate. The highest column density absorbers, the Damped Lyman-α (DLAs) systems, in particular, can be used to determine the cosmic evolution of HI gas in the Universe, ΩHI, and the global metallicity in the gas phase. Since stars are known to form from HI gas, ΩHI provides an indirect tracer of the history of star formation. Recent results from several parallel VLT programmes aiming at determining the cosmological evolution of the metallicity in the neutral gas phase are presented.
Chemically Consistent Evolutionary Synthesis Modelling of Galaxies
Authors: Fritze Uta , García Thorsten Tepper
Published: April 2007

We present our chemically consistent GALEV Evolutionary Synthesis models for galaxies and point out differences to previous generations of models and their effects on the interpretation of local and high-redshift galaxy data.
Starburst Feedback in Local, Massive Galaxies
Authors: Martin Crystal L.
Published: April 2007

Major mergers of gas-rich galaxies, each comparable in mass to the Milky Way, are rare at the present epoch. These events were readily identifed, however, two decades ago in far-infrared sky surveys (Soifer et al. 1986, 1987). Removal of the dust enshrouding these starbursts was almost immediately proposed as an evolutionary path to quasar formation (Sanders 1988). Recent measurements of the stellar velocity dispersion, rotation speed, and stellar surface brightness profile of these mergers suggest ULIRGs are indeed progenitors of field elliptical galaxies (Genzel et al. 2001; Tacconi et al. 2002).
Downsizing in HII galaxies
Authors: Terlevich R. , López J. , Terlevich E.
Published: April 2007

In this work we estimated the statistical age of a set of HII galaxies obtained from the Sloan Digital Sky Survey Data Release Three (SDSS DR3). Applying an inversion method to the observed distribution of an age sensitive parameter such as the equivalent width of (Hα), we estimate the age of the galaxies. We find strong dependence of the age with stellar luminosity, mass and metallicity with the youngest HII galaxies being those with the lowest mass and metallicity. These dependences found among HII galaxies indicate that “downsizing” extends to the low end of the mass distribution of galaxies.
The Rest-Frame Near-Infrared Colors and M/L of Early-Type Galaxies at z = 1
Authors: van der Wel Arjen
Published: April 2007

We present the results of a study of the evolution of the optical and near-IR colors and mass-to-light ratios (M/L) of early-type galaxies from z~ 1 to the present. This exercise is relevant for studies that use photometry of galaxies to infer properties such as stellar masses and star formation histories through comparison with stellar population models. We have dynamical M/L for a sample of 20 early types at z~ 1 with velocity dispersions from deep optical spectroscopy and structural parameters (size and surface brightness) from high-resolution HST imaging. We compare those with 23 early-type galaxies in the Coma Cluster at z=0.02. For both samples rest-frame optical/near-IR photometry is available, from HST and Spitzer in the case of the z~ 1 sample. We find that the M/L evolves faster in the near-IR than expected from most stellar population models, and also that predictions from different models can differ significantly in the near-IR. As a consequence, there is a systematic uncertainty of a factor of two in stellar mass estimates from near-IR photometry for evolved, high-z galaxies. Optical colors provide a less biased indicator of the M/L. Agreement among the models is required before near-IR photometry can be used as a robust tool to estimate galaxy masses without systematic uncertainties.
Mutual Feedback Between Star Formation and Nuclear Activity
Authors: Granato Gian Luigi
Published: April 2007

In this invited contribution I review the justifications for the attempts, currently very popular, to include in semi-analytic models of galaxy formation prescriptions to describe the mutual link between the star formation and nuclear activity in galaxies, which has been for surprisingly long time neglected.
Gaseous Haloes: Linking Galaxies to the IGM
Authors: Fraternali Filippo
Published: April 2007

Recent observations show that spiral galaxies are surrounded by massive and extended haloes of both neutral and ionized gas. These gaseous haloes have peculiar kinematics with respect to their discs: they rotate more slowly and they show an overall inflow motion. Theoretical models of the formation of these gaseous haloes show that they cannot originate solely from a galactic fountain (supernova outflows from the disk); substantial accretion of material from the Intergalactic Medium should play an important role.
The Structure of the Stellar Hosts in Blue Compact Dwarf Galaxies
Authors: Amorín R.O. , Aguerri J.A.L. , Cairós L.M. , Caon N. , Muñoz-Tuñón C.
Published: April 2007

Blue compact dwarf (BCD) galaxies are gas-rich, low-luminosity (Mb≳-18 mag) and compact systems, currently undergoing violent star-formation burst (Sargent & Searle 1970). While it was initially hypothesized that they were very young galaxies (e.g. Sargent & Searle 1970, et al. 1988), the subsecuent detection of an extended, redder stellar host galaxy showed that the vast majority of them are old systems (e.g. Gil de Paz et al. 2003,2005). BCDs play an important role for understanding the process of galaxy formation and evolution.

The structural properties of the low surface brightness stellar host in BCDs are often studied by fitting r1/n models to the outer regions of their radial profiles. The limitations imposed by the presence of a large starburst emission overlapping the underlying component makes this kind of analysis a difficult task.

We propose a two-dimensional fitting methodology in order to improve the extraction of the structural parameters of the LSB host Amorín et al. 2006, submitted). A set of ideal simulations are presented in order to test the reliability of the method and to determine its robustness and flexibility. We present the different steps of the method discussing its advantages and weaknesses. We compare the results for a sample of eight objects with those already obtained using a one-dimensional technique (Caon et al. 2005).

We fit a PSF convolved Sérsic model to the BVR images with the GALFIT publicly software (Peng et al. 2002). We restrict the fit to the stellar host by masking out the starburst region and take special care to minimize the sky-subtraction uncertainties. Consistency checks are performed to assess the reliability and accuracy of the derived structural parameters.

We obtain robust fits for all the sample galaxies, all of which, except one, show low Sérsic indices n—very close to 1—with good agreement in the three bands. These findings suggest that the stellar hosts in BCDs have near-exponential profiles. Since the Sérsic index n of host galaxies is important in the context of the possible structural and evolutionary connections among the different types of dwarf galaxies, we are currently extending the study to a larger sample of objects. This kind of studies will help us to understand the mechanisms that form and shape BCD galaxies, and how they relate to the other dwarf galaxy classes.
Star Formation and Threshold in Nearby Galaxies Observed with GALEX
Authors: Boissier Samuel ,   the GALEX team
Published: April 2007

Star formation on galactic scales is the process driving the evolution of galaxies. It is important to understand its various aspects in the nearby universe to properly interpret high redshift observations, and to construct correct models of the evolution of galaxies. Combining UV (GALEX) and infrared (IRAS) data for 43 nearby spatially resolved galaxies with corollary data (HI,CO), we study the star formation law (“Schmidt” law). The absence of a “threshold radius” in the UV supports the idea that star formation proceed at low gas densities and that the usual threshold observed in H-alpha profiles is a small-number statistic effect.