Galaxy mass, cluster-centric distance and secular evolution: their role in the evolution of galaxies in clusters in the last 10 Gyr

INAF – Osservatorio Astronomico di Brera, via Brera 28, 20121 Milan, Italy
e-mail: anand.raichoor@brera.inaf.it; stefano.andreon@brera.inaf.it

Received: 22 February 2012
Accepted: 15 May 2012

Abstract

Context. Galaxy mass and environment are known to play a key role in galaxy evolution: studying galaxy colors as a function of redshift, galaxy mass, and environment offers a powerful diagnosis to disentangle the role of each.

Aims. We study the simultaneous dependence of the fraction of blue galaxies f_blue on secular evolution, environment, and galaxy mass with a well-controlled cluster sample. We are thus able to study the evolution and respective role of the cessation of star formation history (SFH) in clusters caused by galaxy mass (“mass quenching”) or by environment (“environmental quenching”).

Methods. We defined an homogenous X-ray selected cluster sample (25 clusters with 0 < z < 1 and one cluster at z ~ 2.2), having similar masses and well-defined sizes. Using multicolor photometry and a large spectroscopic sample to calibrate photometric redshifts, we carefully estimated f_blue for each cluster at different galaxy mass and cluster-centric distance bins. We then fitted the dependence of f_blue on redshift (z), environment (r/r₂₀₀) and galaxy mass (M) with a simple model.

Results.f_blue increases with cluster-centric distance with a slope α = 1.2_-0.3^+0.4, decreases with galaxy mass with a slope β = -3.8_-0.5^+0.6, and increases with redshift with a slope γ = 3.3_-0.6^+0.7. The data also require for the first time a differential evolution with galaxy mass of f_blue with redshift, with lower mass galaxies evolving slower by a factor ζ = -3.9_-1.1^+0.9.

Conclusions. Our study shows that the processes responsible for the cessation of star formation in clusters are effective at all epochs (z ≲ 2.2), and more effective in denser environments and for more massive galaxies. We found that the mass and environmental quenchings are separable, that environmental quenching does not change with epoch, and that mass quenching is a dynamical process, i.e. its evolutionary rate is mass-dependent. Our study extends the downsizing-like scenario, where the most massive galaxies have their properties set at a very high redshift, to the cluster environment and all galaxies. It illustrates the need to disentangle galaxy mass and cluster-centric distance to properly estimate the behavior of f_blue in clusters.