Environment-driven evolution of galaxies in CLASH-VLT clusters

The analysis of data from recent large spectroscopic and photometric surveys has shown that galaxy properties have a bimodal distribution (e.g., Kauffmann et al. 2003). Two main populations of galaxies can be identified, the bulge-dominated, high-mass, red galaxies with low star formation rate (SFR), and the disk-dominated, low-mass, blue, and high-SFR galaxies. Blue galaxies are the dominant population at high redshifts and in low-density environments, while red galaxies take over at lower redshifts and in high-density environments. One of the key question in this context is whether these correlations are intrinsic of the galaxy populations from their formation epoch (’nature’ hypothesis) or they are the result of an environment- driven evolution (’nurture’ scenario). In this context, the analysis of galaxy popu- lations in massive clusters, characterized by the highest number densities in the Universe, is an ideal tool to shed some light on galaxy evolution, since clusters offer rather extreme physical conditions for the galaxies they host. My work has been focused on investigating the mechanisms which drive the evolu- tion of galaxies in clusters from the Cluster Lensing And Supernova survey with Hubble (CLASH; http://www.stsci.edu/ postman/CLASH/Home.html, P.I.: M. Postman) sample and, more specifically, in the subsample of clusters with spectro- scopic follow-up from the CLASH-VLT survey (P.I.: P. Rosati) in the redshift range z ∼ 0.2 − 0.5,. These spectroscopic data are complemented by wide-field images obtained with Subaru in five photometric bands (B, V, R, I and z) and by Hubble Space Telescope ACS and WFC3 observations in 16 optical/IR bands in the central regions of clusters.This thesis is organized as follows. In Chapter 2 I present the data used in this thesis. In particular I introduce the CLASH survey and its follow-up survey, CLASH-VLT. I describe how I derived the galaxy properties used in this work, focusing in particular on the data available for two of the CLASH clusters: MACS1206-0847 (hereafter M1206) and Abell 209 (here- after A209) . In Chapter 3 I focus on how the environment shapes the galaxy stellar mass function in the higher redshift cluster M1206. I also compare the number, stellar and total density profiles in this cluster. By combining these informations, I set con- straints on the evolutionary processes at work in M1206. In Chapter 4 I analyze the distribution of galaxy stellar masses and the mass density profiles in the cluster Abell 209 at lower redshift than M1206. I also study some properties of the ICL in A209, in order to shed some light on which processes form the ICL and what type of galaxies are its progenitors. To investigate further the evolution of galaxies in A209, I also carry out the dynam- ical analysis of the orbits of passive galaxies. To discriminate between different quenching mechanisms into shaping the evolu- tion of galaxies in this cluster, I also analyze the distribution of galaxy sizes. In Chapter 5 I summarize the results obtained in the two clusters and draw my conclusion on which are the main processes that shape galaxy evolution on how they depend on redshift.