Evolution of Group Galaxies from the First Red-Sequence Cluster Survey

TL;DR

This study analyzes how the fraction of red galaxies in groups evolves from redshift 0.15 to 0.52, revealing that galaxy stellar mass predominantly influences this evolution and that environmental factors also play significant roles, especially for lower-mass galaxies.

Contribution

It provides a comprehensive analysis of red galaxy fraction evolution in galaxy groups, highlighting the dominant role of stellar mass and environmental effects, with evidence of group down-sizing.

Findings

Red galaxy fraction is already high by z~0.5, indicating early formation.

Stellar mass is the primary factor influencing red fraction.

Environmental parameters affect lower-mass galaxies more significantly.

Abstract

We study the evolution of the red galaxy fraction (f_red) in 905 galaxy groups with 0.15 < z < 0.52. The galaxy groups are identified by the `probability Friends-of-Friends' algorithm from the first Red-Sequence Cluster Survey (RCS1) photometric-redshift sample. There is a high degree of uniformity in the properties of the red-sequence of the group galaxies, indicating that the luminous red-sequence galaxies in the groups are already in place by z~0.5 and that they have a formation epoch of z>2. In general, groups at lower redshifts exhibit larger f_red than those at higher redshifts, showing a group Butcher-Oemler effect. We investigate the evolution of f_red by examining its dependence on four parameters, which can be classified as one intrinsic and three environmental: galaxy stellar mass (M_*), total group stellar mass(M_{*,grp}, a proxy for group halo mass), normalized group-centric radius (r_grp), and local galaxy density (Sigma_5). We find that M_* is the dominant parameter such that there is a strong correlation between f_red and galaxy stellar mass. Furthermore, the dependence of f_red on the environmental parameters is also a strong function of M_*. Massive galaxies (M_* > 10^11 M_sun) show little dependence of f_red on r_grp, M_{*,grp}, and Sigma_5 over the redshift range. The dependence of f_red on these parameters is primarily seen for galaxies with lower masses, especially for M_* < 10^{10.6} M_{sun}. We observe an apparent `group down-sizing' effect, in that galaxies in lower-mass halos, after controlling for galaxy stellar mass, have lower f_red. We find a dependence of \fred on both \rgrp and \SigmaF after the other parameters are controlled. At a fixed \rgrp, there is a significant dependence of f_red on Sigma_5, while r_grp gradients of f_red are seen for galaxies in similar Sigma_5 regions. This indicates .....