The evolution of the galaxy mass assembly and star formation activity from z=1 to z=0 as a function of environment

Aim of this thesis is to investigate the role of the galaxy mass and environment in shaping the galaxy properties, characterising the history of stellar evolution, the stellar mass assembly, and the structure development of galaxies in different environments, by tracing the star formation rate, the total stellar mass of galaxies and the morphology at different redshifts. The data exploited in this thesis come from four surveys which focus on different environments and redshifts in the range z=0 to z=1: the Wide-field Nearby Galaxy-cluster Survey (WINGS - Fasano et al. 2006), the Padova-Millennium Galaxy and Group catalogue (PM2GC - Calvi, Poggianti, Vulcani 2011), the IMACS Cluster Building Survey (ICBS - Oemler et al. 2012a,b, in preparation), and the ESO Distant Cluster Survey (EDisCS - White et al. 2005). First, analysing a sample of galaxies from EDisCS and using field data from literature, I study the ongoing Star Formation Rate (SFR) and the Specific Star Formation Rate (SSFR) at z=0.4-0.8 for different stellar masses and environments. In mass-limited samples, the SFR at a fixed galaxy mass declines with time. The SSFR declines as galaxy stellar mass increases, showing that the current star formation contributes more to the fractional growth of low-mass galaxies than high-mass galaxies. The median SFR is lower in cluster star-forming galaxies than in the field, by a factor of ~1.5. I conclude that the average SFR in star-forming galaxies varies with galaxy environment at a fixed galaxy mass. Subsequently, using both WINGS and EDisCS data, I examine the morphology-mass relation (the way the proportion of galaxies of different morphological types changes with galaxy mass), and find it strongly depends on redshift. Both at z=0 and z~0.6, ~40% of the stellar mass is in elliptical galaxies. Another ~43% of the mass is in S0 galaxies in local clusters, while it is in late-types in distant clusters. Using data from all the surveys, I then analyse the galaxy stellar mass function in mass-limited samples, focusing on a number of aspects, such as the role of the global and local environment in shaping the mass distribution, its evolution in clusters compared to the field, and what simulations predict for galaxies located in haloes of different mass. The main results are: (1) at intermediate redshift I do not detect any dependence of the mass function on the global environment: galaxies in clusters, groups and in the field are regulated by similar mass distributions, at least for M_star/M_sun >10.5. (2) In clusters, I investigate the evolution of the total mass function from z~0.6 to z\sim 0, and I find that in the local Universe there are proportionally more low-mass galaxies than at high-z. This evolution is mainly driven by the galaxy mass growth due to star formation and by morphological transformations from one type to the other. (3) I contrast the evolution of the mass function in clusters and in the field from z~ 0.4 and z~ 0.6 to z~ 0 and find that it is very similar, hence independent of global environment. (4) I analyse the role of the local galaxy density in shaping the mass function, both at low and intermediate redshift, in clusters and in the field. Galaxies in different local density regions follow different mass functions. This result, coupled with point (1) above, suggests that galaxy properties such as galaxy mass are not much dependent on halo mass, but do depend on local scale processes. (5) Simulations are able to reproduce the observed mass function for field galaxies in the local Universe, while they fail in reproducing clusters at both low- and high-z and the field at high-z, suggesting that the current treatment of star formation performed in simulations has to be improved to well reproduce the galaxy mass distribution at different epochs and in different environments. Having found that both the morphological fractions and the mass functions vary with redshift, I then study how this evolution influences the ellipticity distribution of cluster early-type galaxies, finding that the variation with redshift is due to a change both of the median and of the shape of the distributions with redshift. The evolution of early-type galaxies is not simply related to the different mass distributions at high- and low-z, but it is mainly related to the evolution of the morphological mix with redshift and hence to the relative contribution of ellipticals and S0s at the two epochs. Finally, I present the spectroscopic analysis of galaxies in a field containing a z=0.96 cluster, Cl 1103.7-1245C, as part of the EDisCS project, for which I carried out the data reduction. I characterise the galaxy population of the two structures I singled out (the ``main cluster'' and a ``secondary structure'') and I compare my results with the galaxy populations of the other EDisCS clusters that have comparable values of velocity dispersions, but are located at lower redshifts. In general, the properties of the main cluster are in line with the other clusters and the expected evolution, while the secondary structure is an outstanding system, composed only of low-mass, strongly star-forming and morphologically peculiar galaxies. To conclude, the role of the galaxy stellar mass is undisputed in driving galaxy evolution: galaxies are characterised by a wide range of total stellar masses and the evolution of their properties strongly depends on their mass. Anyway, mass and environment are not independent. The environment, besides affecting some galaxy properties, is partially able to influence the mass distribution: more massive galaxies are preferentially found at higher densities.