We perform a statistical analysis to study the infall of galaxies onto groups and clusters in the nearby Universe. The study is based on the UZC/SSRS2 group catalogs and galaxy peculiar velocity data. We find a clear signature of infall of galaxies onto groups in a large range of scales 5 Mpc h$^{-1} < r < 30$ Mpc h$^{-1}$. We obtain a significant increase of the infall amplitude with group mass derived from virial equilibrium and from the luminosity of the member galaxies. We compare the observational results with mock catalogs derived from numerical simulations of semi-analytical models where we obtain a behavior similar to observations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A multi-object spectroscopy follow-up survey of galaxy clusters selected from the Red-sequence Cluster Survey (RCS) is being completed. About forty clusters were chosen with redshifts from 0.15 to 0.6, and in a wide range of richnesses. One of the main science drivers of this survey is a study of internal dynamics of clusters. We present some preliminary results for a subset of the clusters, including the correlation of optical richness with mass, and the mass-to-light ratio as a function of cluster mass.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Surface brightness measurements of the diffuse intracluster light (ICL) in centrally concentrated, relaxed clusters have demonstrated that stars bound only to the cluster potential can contain anywhere from 5 to 50% of the total cluster flux. These stars are a by-product of the evolution of galaxies in clusters, and can be used to constrain models for the structure and evolution of clusters and their member galaxies. The ICL will be an important test of cosmological models as it is a baryonic component of clusters that is likely to evolve with redshift. To learn about these processes we are undertaking a program to measure the characteristics of the ICL (total flux, color, and substructure) as a function of cluster mass, morphology, and redshift. We have obtained data for a sample of 10 clusters at low and moderate redshifts. We discuss here our preliminary results for one cluster in that sample, A3888. With 4-5 hour integration times on-source per filter (V & gunn-r), we reach a 1 sigma surface brightness limit of 29.9 mag/arcsec$^{2}$ in the V band. We have identified an intracluster light component that is $\sim10\%$ of total cluster light, extends to 600 kpc from the center of the cluster, and is redder in color than the cluster galaxies ($V-r = 0.4$ near the center, increasing to $V-r = 0.8$ at r = 500 kpc). In addition we find 3 low surface brightness features which are blue ($V-r \simeq 0$), and in total are equivalent to one $m_V = 20.8$ mag galaxy.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

We present the ability of weak lensing surveys to locate massive clusters. We use both analytic models of dark matter halos and mock weak lensing surveys generated from a large cosmological $N$-body simulation. We find that, for a weak lensing survey with a galaxy number density of $n_g=30$ arcmin$^{-2}$ with a mean redshift $z=1$, the mean number of galaxy clusters which are expected to be identified is $N({\rm S/N}>4)=7$ per 1 deg$^2$. Weak lensing surveys thus provide a reasonably efficient way to search for massive clusters. We also describe our project on the weak lensing cluster survey exploiting Suprime-Cam (the wide-field prime focus camera on the 8m Subaru telescope), called Suprime-33 and present current status. We also present results from its pilot survey in the Suprime-Cam 2.1 deg$^2$ field.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Clusters of galaxies are the largest bound gravitational systems in the universe. They outline the large-scale structure and thus are able to test predictions of cosmological models. Detailed studies of galaxy populations in clusters at high $z$ offer insights into galaxy evolution as a function of look-back time. Unfortunately, large homogeneous samples of galaxy clusters only exist at redshifts $<$0.5. There are around 1000 candidate clusters with photometric or otherwise estimated redshifts above 0.5, but spectroscopically confirmed clusters are still scarce in this redshift regime. Some clusters with $z>1$ have recently been identified from X-ray surveys.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present first results for spectroscopic observations of galaxies in 4 clusters at $z=0.7-0.8$ and one cluster at $z=0.5$ observed by the ESO Distant Cluster Survey (EDisCS). Our spectroscopic catalogues contain 236 cluster members of our 5 clusters, and the number of members per cluster ranges from 30 to 67. Our cluster velocity dispersions are between $\sim$400 and over 1000 $\rm{km s}^{-1}$. Galaxy redshift distributions are found to be non-Gaussian and we find evidence for significant substructure in two clusters, one at $z \sim 0.79$ and another at $z \sim 0.54$; both clusters have velocity dispersions exceeding 1000 $\rm{km~s}^{-1}$. These systems have clearly not yet virialised at these epochs in qualitative agreement with CDM scenarios and their cluster velocity dispersions should not be used in the measurement of cluster mass. Our clusters have a wide range of different cluster velocity dispersions, richnesses and substructuring, and our spectroscopic data set is allowing a comprehensive insight into cluster galaxy evolution as a function of redshift and environment.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present multi-object spectroscopic observations from FORS1 mounted at the VLT for 5 clusters detected in the ESO Imaging Survey. Together with the results for three other clusters presented previously, we confirm a total of 6 out of 8 clusters with estimated redshift $z_{MF}\geq0.6$. The spectroscopic redshifts are in good agreement with the estimated ones.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We use preliminary results of WINGS survey (Fasano et al.) to obtain determinations of optical scaling relations for galaxy clusters. Passing from one- to two- parameter scaling relations we pay particular attention to the Kormendy relation (KR) and to the Fundamental Plane (FP) of galaxy clusters, comparing them with scaling relations of elliptical galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the preliminary result of our project, consisting in studying the properties of a large sample of galaxy clusters. The Münster Red Sky Survey, which is a large galaxy catalogue covering an area of about 5000 square degrees on the southern hemisphere, serves as our observational basis. It is complete up to $r_F=18^m.3$. Creation of a cluster catalogue is the first step of our investigation. We propose to use the 2D Voronoi tessellation technique for identifying galaxy clusters in this 2D catalogue. Points with high values of the inverse Voronoi tessel area will be regarded as galaxy cluster centroids. We show that this approach works correctly.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We analysed 246 scanned ACO clusters and we do not find any dependence of galaxy cluster ellipticity on redshift.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Most of the baryons in the universe remain undetected. They are thought to be floating in intergalactic space, and their thermal state is highly uncertain. The only places where we have reasonably complete observations of the overall baryon population are in clusters of galaxies, where the baryons reveal themselves through their X-ray emission. There we find that only about 10% of the baryons have turned into stars, probably because feedback processes intervene to prevent more baryons from condensing. These galaxy formation processes seem to have left an imprint on the thermal state of the intracluster medium, but in order to interpret that imprint, one needs to pay close attention to how entropy develops in the intergalactic gas. Many of the global properties of clusters turn out to be determined primarily by the entropy threshold for cooling within a Hubble time. However, XMM-Newton observation are revealing a sort of altered similarity among the entropy profiles of clusters seeming to indicate that galactic winds may have smoothed the local intergalactic medium before it accreted onto clusters.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

I review recent results of cosmological hydrodynamic simulations for clusters of galaxies. Such simulations have developed into an increasingly powerful tool to make theoretical predictions for clusters, and to confront them with observations. I focus, in particular, on the continuing challenge to reproduce the observed cluster X-ray scaling relations in CDM simulations. Self-consistent simulations that include radiative cooling, star formation and supernova feedback generally overpredict the X-ray luminosity on group scales and exhibit overly strong cooling flows. Solving these problems may require the consideration of more physics in cluster simulations, for example thermal conduction or heating by a central AGN.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We use numerical simulations of galaxy clusters to study the dynamical and thermal evolution of the ICM from high redshift to the present time. We measure the properties of the satellites accreting on the cluster main progenitor and then measure their self-bound mass fraction as a function of time after the merging. We also calculate the mean properties of their orbits and investigate the time evolution of their internal velocity dispersion and gas temperature. We measure and model the mean pericentric and apocentric times, distances and velocities. Finally we show how the properties of the ICM at redshift zero can be understood by decomposing them as a function of the cluster merging history.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present results from a set of high ($512^3$ effective resolution), and ultra-high ($1024^3)$ SPH adiabatic cosmological simulations of cluster formation aimed at studying the internal structure of the intracluster medium (ICM). We discuss the radial structure and scaling relations expected from purely gravitational collapse, and show that the choice of a particular halo model can have important consequences on the interpretation of observational data. The validity of the approximations of hydrostatic equilibrium and a polytropic equation of state are checked against results of our simulations. We also show the first results from an unprecedented large-scale simulation of 500 $h^{-1}$ Mpc and $2\times 512^3$ gas and dark matter particles. This experiment will make possible a detailed study of the large-scale distribution of clusters as a function of their X-ray properties.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

To understand cluster formation and evolution it is important to understand the evolution of cluster substructure. The work described here focuses upon a set of fully self-consistent numerical simulations within a $\Lambda$CDM cosmology. Within the simulations we follow in detail the temporal and spatial properties of individually tracked satellite galaxies. The host galaxy clusters were chosen to sample a variety of formation histories, ages, and triaxialities. Despite their obvious differences, we find striking similarities within the associated substructure populations. Namely, the satellite galaxy orbital distributions are indistinguishable between the galaxy clusters.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present first results of numerical simulations of the dynamics of all three components of a galaxy cluster: the dark matter, the intracluster gas, and the member galaxies. Our first aim is to understand the enrichment of the gas component by studying various interaction processes between cluster galaxies and the intracluster gas, notably ram-pressure stripping and galactic winds. Our second aim is to find out how fast metals originating from such interaction processes diffuse throughtout the cluster, in order to understand observed metallicity maps of galaxy clusters obtained from X-ray observations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Metal enrichment of intracluster medium (ICM) is reanalysed in the hierarchical galaxy formation scenario. In order to investigate metal abundances of $\alpha$ and iron-peak elements, we incorporate metal production processes by type Ia supernovae (SNe Ia) as well as type II supernovae (SNe II) into the GALFORM model of semi-analytic galaxy formation. We find that a top-heavy initial mass function (IMF) of stars with a power index $x\simeq 0.35$ for starburst is required under the constraint that the IMF for quiescent disc star formation is the Kennicutt IMF. Our model shows an only mild evolution of [Fe/H] as suggested by a recent observation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A new cosmological multidimensional hydrodynamic and N-body code based on an Adaptive Mesh Refinement scheme is described and tested. The hydro part is based on modern high-resolution shock-capturing techniques, whereas N-body approach is based on a Particle Mesh method. The code has been specifically designed for cosmological applications.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We study the effects of radiative cooling, star formation and stellar feedback on the properties and evolution of galaxy clusters using high-resolution Adaptive Mesh Refinement N-body+gasdynamics simulations of clusters forming in the $\Lambda$CDM universe. Cooling leads to the condensation of gas in the inner regions of clusters, which in turn leads to steepening of the dark matter profile. The cooling gas is replaced by the higher-entropy gas from the outer regions, which raises the entropy and temperature of gas in the cluster core. The magnitude of these effects is likely overestimated in the current simulations because they suffer from the overcooling problem: a much larger fraction of baryons is in the form of cold gas and stars than is observed. We find that the thermal stellar feedback alone does not remedy this problem. Additional ad-hoc preheating can lower the amount of cold gas but a simple uniform preheating results in incorrect star formation history, as it delays the bulk of star formation until $z<1$. Our analysis shows that the overcooling in a cluster as a whole is really the overcooling in the central galaxy and its progenitors at high redshifts. This indicates that an additional heating mechanism that can continuously heat the gas in the cluster core is required to reproduce the observed cluster properties. Energy injection by the Active Galactic Nuclei, which may provide such heating, may thus be an important missing ingredient in the current theoretical models of cluster formation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html