We analyse statistically the infall of mass onto clusters in $\Lambda$-CDM numerical simulations. Also, we consider numerical simulations which include galaxy formation through semi-analytical models to compare the expected infall of mass and galaxies. We find the most probable values at $V \sim 300-400$ km/s and a significant tail of large infall velocities ($V > 1000$ km/s). The flow onto cluster is more pronounced for high local density regions. Mass and galaxies behave similarly although with a slightly lower amplitude.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The last decade has seen an explosion in the number and scope of wide-field surveys. The data provided by these surveys will greatly increase our understanding of the relationships between the outskirts and the cluster centers and the field. I summarize the status of current deep-wide optical surveys and describe the plans for the next generations of surveys, with particular emphasis on the applications of these surveys to weak gravitational lensing. As a concrete example of such a survey, I will present results from the Deep Lens Survey (DLS).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Gas in galaxy centers may be irradiated by far-ultraviolet, X-ray photons or both. We discuss the observational line diagnostics for PDRs (FUV) and XDRs (X-ray).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We carried out a spectroscopic survey of a sample of 59 Seyfert nuclei (observed both in the northern and in the southern hemisphere) around the stellar absorption lines of Calcium II at 8498.02, 8542.09 and 8662.14 Å (CaT). Our main goal is to determine their stellar velocity dispersions. These measurements, along with photometric information, will allow us to obtain the M/L ratio, useful to determine the nature of the ∼33% of “ambiguous” Seyfert 2.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The properties of stellar populations in the centers of nearby lenticular galaxies are investigated by means of 2D spectroscopy. All the galaxies are divided into 4 groups depending on the environment type; every subsample contains more than 10 galaxies. Clear distinctions between the mean stellar ages and abundance ratios are found both for the nuclei and for the bulges of the S0s in the different environments.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

According to the current paradigm, galaxies form and reside in extended cold dark matter (CDM) halos and in turn are key tracers of cosmological structure. Understanding how different types of galaxies occupy halos of different masses is one of the major challenges facing extragalactic astrophysics. The observed galaxy properties depend on the environment surrounding the galaxy. Within the framework of most galaxy formation models the environmental dependence of the galaxy population is mainly due to the change of the halo mass function with large-scale environment. Such models make precise predictions for how galaxy clustering should depend on environment. We will illustrate this by presenting analytical models of dark matter and galaxy clustering along with results obtained from numerical simulations. With these results we can hope to obtain a better understanding of the link between galaxies and dark matter and thereby constrain galaxy formation models.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A single web link is provided to a maintained site giving detailed descriptions of telescope and instrumentation combinations available – and planned for the near future – at Gemini South, CTIO, SOAR and SMARTS for observers of AGN.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the analysis of Hubble Space Telescope blue spectra at intermediate spectral resolution for the nuclei of 23 nearby disk galaxies. These objects were selected to have nebular emission in their nuclei, and span a range of emission-line classifications as well as Hubble types. Here we focus on the stellar population as revealed by the continuum spectral energy distribution measured within the central 0.″13 (∼8 pc) of these galaxies. The data were modeled with linear combinations of single-age stellar population synthesis models. The large majority (∼80%) of the surveyed nuclei have spectra whose features are consistent with a predominantly old ($\gtrsim 5 \times 10^9$ yr) stellar population. Approximately 25% of these nuclei show evidence of a component with age younger than 1 Gyr, with the incidence of these stars related to the nebular classification. Successful model fits imply an average reddening corresponding to AV∼0.4 mag and stellar metallicity of (1–2.5)$Z_\odot$. Our findings reinforce the picture wherein Seyfert nuclei and the majority of low-ionization nuclear emission-line regions (LINERs) are predominantly accretion-powered, and suggest that much of the central star formation in HII nuclei is actually circumnuclear.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present results from new high angular resolution observations of the neutral hydrogen absorption using global VLBI, MERLIN, and VLA observations of the peculiar radio galaxy 3C 293. These results reveal extensive HI absorption against the inner kiloparsec of the radio jet in this source over a wide range of angular scales. In additional to these sub-arcsecond resolution radio observations we also present infrared imaging of the jet.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present and discuss results concerning a study of stellar populations in the galaxies belonging to CL 0048-2942, a cluster at intermediate redshift (z = 0.64), and to the field. This study gives insight on the evolutionary stage of the cluster galaxies at different radial distances from the cluster centre. We find a population gradient within the cluster: centre galaxies host older stars whereas galaxies located towards the cluster outskirts are predominantly made of less evolved stars. This effect is even more pronounced as we move outside the cluster, into the field. This is interpreted as star formation being more intense in the field, or rather, suppressed within the cluster, particulary as we move towards its centre.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present results of our wide-field redshift survey of galaxies in a 285 square degree region of the Shapley Supercluster (SSC).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

There is now firm evidence that the ICM consists of a mixture of hot plasma, magnetic fields and relativistic particles. The most important pieces of evidence for non-thermal phenomena in galaxy clusters come from the diffuse Mpc-scale synchrotron radio emission (radio halos), observed in a growing number of massive clusters (Feretti 2003), and from hard X-ray (HXR) excess emission (detected in a few cases), which can be explained in terms of IC scattering of relativistic electrons off the cosmic microwave background photons (Fusco-Femiano et al. 2003). There is now growing evidence that giant radio halos may be naturally accounted for by synchrotron emission from relativistic electrons reaccelerated by some kind of turbulence generated in the cluster volume during merger events (Brunetti 2003). With the aim of investigating the connection between thermal and non-thermal properties of the ICM, we have developed a statistical magneto-turbulent model which describes the evolution of the thermal and non-thermal emission from clusters. We calculate the energy and spectrum of the magne-!tosonic waves generated during cluster mergers, the acceleration and evolution of relativistic electrons and thus the resulting synchrotron and inverse Compton spectra. Here we give a brief description of the main results, while a more detailed discussion will be presented in a forthcoming paper (Cassano & Brunetti, in preparation). Einstein-De Sitter cosmology, $H_0=50$ km s$^{-1}$ Mpc$^{-1}$, $q_0=0.5$, is assumed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigate the interplay between active nuclei and their surrounding ISM by interferometric radio continuum and mm line observations at high angular resolution and high sensitivity of a sample of active galaxies (e.g. NGC3718), carried out with MERLIN, EVN and the IRAM Plateau de Bure interferometer. They are part of an ongoing international study-NUGA (NUclei of GAlaxies)-about the nature, i.e. basically the fueling mechanisms, of nearby active galaxies. The mm line observations provide information about the distribution and kinematics of the molecular gas in these galaxies, which are regarded to be an important part of the matter feeding the central engine. We find a variety of molecular gas structures in our sample ranging from spirals, bars, warped disks, rings to asymmetric disks. The MERLIN/EVN measurements at 18 cm, as well as 6 cm, allow us to investigate the nature of the central engine itself. Also, the radio observations unveil extended structures on all observed angular scales (from VLA to MERLIN and EVN), like jets, diffuse components, as well as compact features. Moreover, the spectra are flat to steep, depending on the respective source components. The combination of the mm line and radio continuum results allow us to discuss possible interactions between the observed jets and the surrounding interstellar medium.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have analized XMM-Newton data of A2199, a nearby ($z\,=\,0.030$), relaxed, rich cluster of galaxies, whose X-ray emission is strongly peaked on the central galaxy, NGC6166, suggesting the existence of a cluster cool core (Peres et al. 1998). The background subtraction is performed using an observation characterized by features similar to those of the A2199 observation. We have selected, in the XMM-Newton archive, a field observation presenting the following properites:

[bull ] duration of about 90 ksec;

[bull ] performed with the same filter as the A2199 observation;

[bull ] characterized by a galactic HI column density and a soft X-ray background, the latter being calculated from the ROSAT All-Sky survey diffuse background maps, which differ from those of the A2199 observation ($N_H\,=\,8.7 \times 10^{19}\,\,{\rm cm}^{-2}, R_{45}\,=\,208.2 \times 10^{-6}\,\,{\rm cts/arcmin}^2$) by 3% and 30% respectively.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In this paper we interpret C and X-band radio continuum observations of a sample of Markarian galaxies. The results are briefly discussed. Seyfert 2 galaxies show sistematically higher HI mass-to-blue magnitude than Seyfert 1 galaxies, as well as higher radio to far-infrared luminosities. The observational properties are interpreted in terms of simple non-thermal and dust emission. We obtained radio brightness temperatures, equipartion magnetic fields and total magnetic densities for the disks. Upper limits for thermal densities are derived from simple free-free emission. Star formation rates and mean supernova rates are estimated for individual Markarian galaxies. The SFR values of the most luminous Markarian galaxies are considerably higher than those found in compact blue dwarf galaxies and also in gas-rich, early-type spirals.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a unique multiwavelength dataset of the Abell 901/902 supercluster at $z=0.16$. The environment of the structure is well characterized by weak lensing analysis, galaxy dynamics, and X-ray imaging, and we examine how galaxy properties correlate with these measures of environment. We examine the star-formation–density relation and find a surface mass density threshold above which star-formation in supercluster galaxies is truncated, and that this transformation affects primarily the faint end of the star-forming galaxy population (down to $M^*+6$). In addition, we present a preliminary dynamical analysis of the spectroscopic sample ($n\sim 300$ galaxies), revealing a bimodal distribution of galaxy velocities and significant substructure.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present Chandra observations of the nuclear region of nearby inactive galaxies. The sample is selected based on the absence or weakness of optical emission lines in the nucleus. X-ray nuclei are detected in four out of six galaxies. This result, along with previous observations, suggests that more than half of galaxies, for which no evidence for nuclear activity is known, possess an ultra-low-luminosity “active” nucleus. X-ray emission from hot gas is detected in at least four galaxies. We estimate the Bondi accretion rate from the gas density, temperature, and central black hole mass and suggest that the accretion luminosity is not simply determined by the Bondi rate.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the initial results of a deep submillimeter survey of ten $z\sim 1$ galaxy clusters with the SCUBA bolometer array on the JCMT. Recently, an excess number of dust enshrouded starbursts in high-redshift galaxy cluster fields was reported (Best 2002) and has been interpreted as increased star-formation within young clusters. An alternative explanation is that these starbursts are background objects behind clusters with enhanced lensing cross-sections, over that predicted from simple lensing models, so-called “super-lenses” seen in recent optical cluster surveys. To investigate this issue, we are studying a set of clusters which show strong optical arcs (super-lenses) and a set of clusters of equal redshift and richness but which are not super-lenses. The preliminary results, based on 50% of the sample, tentatively suggest that, while the dusty starbursts are limited to the super-lensing cluster fields, they are not background objects but lie within the clusters themselves. Cluster-cluster merging offers a means of increasing both the lensing cross-section, thereby accounting for the multiple strong optical arcs, and increasing the star formation within the clusters through galaxy interactions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Based on our previous work about a co-evolution of massive black holes (MBH) and their host spheroids, we estimate the cosmic star formation history associated with AGN accretion by ROSAT X-ray All sky surveys. We show: 1) the total amount of star formation associated with MBH growth is at least half of the net star formation at high redshift, which probably totally missed by the current UV/optical deep surveys; 2) the FIR emission from the dust heated by star formation on-going during the MBH growth could be a significant energy source for SCUBA populations; 3)the peak redshift of the massive spheroid formation in this case is around 1.5, not necessary to be at much higher redshift.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigate the broadband optical emission of diffuse intergalactic stars in galaxy clusters at $z\sim0.25$ by means of an image stacking technique. The images of 654 clusters, selected with the max-BCG algorithm from a subsample of the SDSS-Data Release 1 (DR1), have been stacked after masking all the sources detected down to very low S/N. The resulting images in the g, r and i bands provide reliable photometric data at the level of $\gtrsim30$ mag$/\square$” (r band), out to $\gtrsim 600$ kpc from the Brightest Cluster Galaxy (BCG). Our analysis shows that: i) the IntraCluster Light (ICL) is much more concentrated than the galaxy light, contributing $\sim$30% of the total cluster optical emission at $R=100$ kpc, but less than 10% at $R > 500$ kpc; ii) the ICL contributes between 15 and 20% of the total cluster optical luminosity between the optical radius ($\mu_r=25$ mag$/\square$”) of the BCG and 500 kpc; iii) the colours of the ICL are consistent with the global colours of the cluster galaxies, with little evidence for redder g$-$r.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html