The Roles of Mass and Environment in the Quenching of Galaxies

Abstract

We study the roles of stellar mass and environment in quenching the star formation activity of a large set of simulated galaxies by taking advantage of an analytic model coupled to the merger tree extracted from an N-body simulation. The analytic model has been set to match the evolution of the global stellar mass function since redshift z similar to 2.3 and give reasonable predictions of the star formation history of galaxies at the same time. We find that stellar mass and environment play different roles: the star formation rate/specific star formation rate-M-* relations are independent of the environment (defined as the halo mass) at any redshift probed, 0 < z < 1.5, for both star-forming and quiescent galaxies, while the star formation rate -M-halo relation strongly depends on stellar mass in the same redshift range, for both star-forming and quiescent galaxies. Moreover, the star formation rate and the specific star formation rate are strongly dependent on stellar mass even when the distance from the cluster core is used as a proxy for the environment, rather than the halo mass. We then conclude that stellar mass is the main driver of galaxy quenching at any redshift probed in this study, not just at z > 1 as generally claimed, while the environment has a minimal role. All the physical processes linked to the environment must act on very short timescales, such that they do not influence the star formation of active galaxies, but increase the probability of a given galaxy to become quiescent.