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Star clusters are ideal tracers of star formation activity in systems outside the volume that can be studied using individual, resolved stars. These unresolved clusters span orders of magnitude in brightness and mass, and their formation is…
We report a systematic multi-wavelength investigation of environments of the brightest cluster galaxies (BCGs), using the X-ray data from the Chandra archive, and optical images taken with 34'x 27' field-of-view Subaru Suprime-Cam. Our goal…
We present a deep UBI CCD survey using the Palomar 5-m telescope of a sample of high X-ray luminosity, distant clusters selected from the ROSAT All-Sky Survey. The 10 clusters lie at z=0.22-0.28, an era where evolutionary effects have been…
We present 371 galaxy velocities in the field of the very rich cluster Abell 2125 (z~0.25). These were determined using optical spectroscopy collected over several years from both the WIYN 3.5m telescope and NOAO Mayall 4m telescope. Prior…
Central regions of superclusters are the ideal places where to study cluster merging phenomena: in fact the accretion activity is enhanced, as predicted by the cosmological simulations. In this paper I review the case-study of the Shapley…
We derive the luminosity and multiplicity functions of superclusters compiled for the 2dF Galaxy Redshift Survey, the Sloan Digital Sky Survey (Data Release 4), and for three samples of simulated superclusters. We find for all supercluster…
Populations of young star clusters show significant differences even among "normal" disk galaxies. In this contribution I discuss how properties of young cluster systems are related to those of their host galaxies, based on a recent study…
We study the distribution of X-ray selected clusters of galaxies with respect to superclusters determined by Abell clusters of galaxies and show that the distribution of X-ray clusters follows the supercluster-void network determined by…
We present a method to obtain a high-significance detection of relativistic effects on cosmological scales. Measurements of such effects would be instrumental for our understanding of the Universe, as they would provide a further…
The K-band Hubble diagram for a sample of brightest cluster galaxies (BCGs) in the redshift range 0<z<1 shows a very small scatter (0.3 magnitudes r.m.s). The BCGs exhibit very little luminosity evolution in this redshift range: if q_0=0.0…
Using a resimulation technique, we perform high-resolution cosmological simulations of dry mergers in a massive galaxy cluster identified in the Millennium Run. Our initial conditions include well resolved compound galaxy models consisting…
The current consensus on the formation and evolution of the brightest cluster galaxies is that their stellar mass forms early ($z \gtrsim 4$) in separate galaxies that then eventually assemble the main structure at late times ($z \lesssim…
We present an analysis of the merging cluster MACS J1149.5+2223 using archival imaging from Subaru/Suprime-Cam and multi-object spectroscopy from Keck/DEIMOS and Gemini/GMOS. We employ two and three dimensional substructure tests and…
The nonthermal radiation observed from a handfull of clusters of Galaxies is the proof that particle acceleration occurs in the intracluster medium. It is often believed that shock surfaces associated with either mergers of clusters of…
We present the results of deep Chandra, XMM-Newton and Suzaku observations of the nearby galaxy cluster Abell 85, which is currently undergoing at least two mergers, and in addition shows evidence for gas sloshing which extends out to r ~…
We analyse the relation between the dynamical state of a cluster of galaxies and the activity (star formation and AGN) of its members. For the case of Abell 85 we find some evidence for an enhanced activity of both types in substructures…
We study the mass distribution of a sample of 24 X-ray bright Abell clusters through weak gravitational lensing. This method is independent of the dynamical state of the galaxy cluster. Hence, by comparing dynamical and lensing mass…
We test an analytic model for the two-point correlations of galaxy clusters in redshift space using the Hubble Volume N-body simulations. The correlation function of clusters shows no enhancement along the line of sight, due to the lack of…
We use semi-analytic techniques to study the formation and evolution of brightest cluster galaxies (BCGs). We show the extreme hierarchical nature of these objects and discuss the limits of simple ways to capture their evolution. In a model…
Massive star clusters observed in galaxy mergers are often suggested to be progenitors of globular clusters. To study this hypothesis, we performed the highest resolution simulation of a gas-rich galaxy merger so far. The formation of…