The Role of the Environment on Galaxy Evolution

Abstract

Esame finale anno 2016A Milena "Che fai tu, Luna, in ciel? Dimmi, che fai, silenziosa Luna?" -Giacomo Leopardi, Canto notturno di un pastore errante dell'Asia A B S T R A C TAlthough the general picture of how galaxies have formed and evolved through cosmic time is already in place, still many details are missing. An example is represented by a quantitative characterization of the role that environment plays during the evolution of galaxies in determining their observed properties in the local Universe. Local galaxy environment has been thoroughly explored through observations at low redshift and it has recently started to being investigated also in the distant Universe. Moreover, general attention has been increasingly focused on the relation between galaxy evolution and galaxy positions with respect to the large-scale structures of the cosmic web.This work explores how environment (defined both in terms of local overdensities on the Mpc scale around galaxies, as well as in terms of the distribution of galaxy distances from ∼ 10 2 Mpc long cosmic filaments) is observationally related to galaxy properties such as their stellar mass, their star-formation activity, or the presence of Active Galactic Nucleus phenomena. The analysis reported here is performed in a large redshift range, going from the local Universe (z 0.2) to intermediate (z ∼ 0.7) and high-redshifts (z 3). To perform this study, both spectroscopic redshift data sets as well as photometric redshift surveys have been deployed and (particularly for the photometric redshift data sets) a thorough analysis of the effect of their observational issues on the measurement of local and global environment has been executed.The picture that emerges is that high-density environments are favoured places for galaxy evolution, showing an enhanced fraction of massive galaxies which have stopped forming stars and belong to the quiescent population. Galaxies in high-density environments have an increased probability of hosting radio-AGNs (belonging to the ensemble of processes that turn off the star-formation in massive galaxies) and these effects are visible since the start of the decline in the cosmic star-formation history. Large-scale structures, such as the filaments of the cosmic web, have also a role in shaping galaxy evolution and they may represent key places for the pre-processing of galaxies before they enter higher density regions such as the cluster or group environment.As an increasing amount of observational evidence on the relation between the evolution of galaxies and their environment is gathered, a complete solution to the problem of how the local galaxy population has evolved approaches, and the history of galaxies from their formation at the dawn of time to the present day gets closer to being traced. Figure 2 Growth of structures . . . . . . . . . . . . . . . 7 Figure 3 Evolution of the global SFR density . . . . . . . 8 Figure 4 Colour-density relation for VVDS galaxies . . 11 Figure 5 Fraction of M * contained in galaxies as a function sSFR ....