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Published February 2012 | Published
Journal Article Open

The galaxy stellar mass function of X-ray detected groups. Environmental dependence of galaxy evolution in the COSMOS survey


We study the stellar mass distribution for galaxies in 160 X-ray detected groups of 10^(13) < Log(M_(200)/M_⊙) < 2 × 10^(14) 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 M_(200) < 6 × 10^(13) 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).

Additional Information

© 2012 ESO. Received 14 July 2011. Accepted 24 November 2011. Published online 13 February 2012. S.G. acknowledges support from The Netherlands Organization for Scientific Research (NWO) through a VIDI grant. We acknowledge the contributions of the entire COSMOS collaboration; more informations on the COSMOS survey are available at http://www.astr.caltech.edu/~cosmos. S.G. acknowledge H. Boehringer for having contributed to the start of this project and H. Hoekstra, G. Guzzo, J. Brinchmann, S. Weinmann, D. Capozzi, T. Ponman, B. Vulcani and A. Leauthaud for helpful discussion. D.P. acknowledges the kind hospitality of the MPE.

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