The galaxy stellar mass function of X-ray detected groups

Environmental dependence of galaxy evolution in the COSMOS survey^⋆

¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
e-mail: giodini@strw.leidenuniv.nl
² Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
³ INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁴ Laboratoire d’Astrophysique de Marseille, BP 8, Traverse du Siphon, 13376 Marseille Cedex 12, France
⁵ Department of Physics, ETH Zü rich, 8093 Zürich, Switzerland
⁶ California Institute of Technology, MS 249-17 Pasadena, CA 91125, USA
⁷ Institute for the Physics and Mathematics of the Universe, University of Tokyo, 2778582 Kashiwa, Japan

Received: 14 July 2011
Accepted: 24 November 2011

Abstract

We study the stellar mass distribution for galaxies in 160 X-ray detected groups of 10¹³ < Log(M₂₀₀/M_⊙) < 2 × 10¹⁴ and compare it with that of galaxies in the field to investigate the action of environment on the build-up of the stellar mass. We highlight differences in the build-up of the passive population in the field, which imprint features in the distribution of stellar mass of passive galaxies at Log(M/M_⊙) < 10.5. The gradual diminishing of the effect when moving to groups of increasing total masses indicates that the growing influence of the environment in bound structures is responsible for the build-up of a quenched component at Log(M/M_⊙) < 10.5. Differently, the stellar mass distribution of star-forming galaxies is similar in shape in all environments, and can be described by a single Schechter function both in groups and in the field. Little evolution is seen up to redshift 1. Nevertheless at z = 0.2–0.4 groups with M₂₀₀ < 6 × 10¹³ M_⊙ (low-mass groups) tend to have a characteristic mass for star-forming galaxies that is 50% higher than in higher mass groups; we interpret it as a reduced action of environmental processes in these systems. Furthermore, we analyse the distribution of sSFR–Log(M) in groups and in the field, and find that groups show on average a lower sSFR (by ~0.2 dex) at z < 0.8. Accordingly, we find that the fraction of star-forming galaxies is increasing with redshift in all environments, but at a faster pace in the denser ones. Finally, our analysis highlights that low-mass groups have a higher fraction (by 50%) of the stellar mass locked in star-forming galaxies than higher mass systems (i.e. 2/3 of their stellar mass).