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 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.

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

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.

Galaxies in groups and clusters often experience strong tidal forces from its neighbors, expelling a significant amount of matter (stars and gas) to the surrounding environment, giving rise to ‘tidal debris’ features. We present the first experiments in a program of identification of substructures of extragalactic tidal debris elements in images from the HST archive, using wavelet-based multiresolution analysis. Tidal structures in two compact groups of galaxies, HCG 79 (Seyfert's Sextet) and HCG 92 (Stephan's Quintet) have been analyzed so far.

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.

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.

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.

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’.

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.

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 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.

We have observed over 100 interacting galaxies (IGs) with Spitzer IRAC as part of a detailed study of the their properties (see also Zezas, et al. in this volume). The majority of sources are nearby. Precise IRAC imaging photometry of these galaxies finds a wide range of colors in these systems, and correlative spectroscopic data suggests the colors are reflected by composition that is in turn reflective of age; orientation also plays a role. We have also observed a distant pair of interacting galaxies at z=3.01, a HyLIG, EGS20 J1418+5236 (Huagg et al. 2006), and find that, like the nearby systems, it has similar processes at work albeit in a hyperactive way.

To overcome limitations of some previous studies of IGs, we observed two complementary nearby samples, one selected on the basis of galaxy separation, and the other selected on a morphological basis. Figure 1 below is a summary IRAC [3.6um]-[4.5um] versus [5.8um]-[8.0um] color-color plot of these IGs. Five generic regions emerge: ellipticals near (0,-0.1), early-stage IGS around (1.5, -0.1), Seyfert 1s around (1.3, 0.5), Seyfert 2s around (1.5, 1.2), and LINERS/HII galaxies centered at 2.2, 0.2). These systems are each characterized by spectral dust features in the IRAC bands that are strong enough to influence and]or mirror the underlying stellar continuum colors. The arrows suggest possible evolutionary development.

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.

Merger theory, in its extreme form, postulates that ellipticals are the products of mergers of spirals. While the morphology-clustercentric relationship (Whitmore et 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 (Chengalur et 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., Faber et al., 1995), in the same environment we find a homogeneous population of normal red galaxies, that have almost finished their star formation.

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.

The WIde-field Nearby Galaxy-cluster Survey (WINGS) is a long term project whose main goal is to establish the zero point and variance of properties of nearby clusters, and galaxies in them, to be used as a local reference in evolutionary studies.

To achieve such objective, wide-field multiwavelenght photometry and optical spectroscopy has been gathered and analysed for a sample of 77 X-ray emitting nearby galaxy clusters.

This contribution shows the current status of the project.

Complete poster contents is reproduced in “On-line Section” and PDF copy is available in http://web.oapd.inaf.it/wings/Docs/IAU2006_Varela.pdf.

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, 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.

We present XMM-Newton observations of the galaxy cluster Abell 514. This cluster shows a very complex X-ray morphology. Radio observations show that there are six radio sources located inside the cluster. This makes it possible to determine the magnetic field strength using the Faraday rotation method. This cluster is an example for the hierarchical growth of structure and a very interesting object for studying the correlation between magnetic field strength and X-ray properties.