The Color Bimodality in Galaxy Clusters since z = 0.9

TL;DR

This study investigates how the color distribution of galaxies in clusters evolves from redshift 0.9 to 0.45, revealing a decrease in blue galaxies over time and insights into galaxy infall and star formation activity.

Contribution

It provides a detailed analysis of the evolution of galaxy colors in clusters over a significant redshift range using a large, homogeneous sample, highlighting the nature of the blue galaxy population.

Findings

Red galaxy fraction decreases with increasing redshift.

Blue galaxies are consistent with normal spirals and redden over time.

Starburst galaxies contribute less than 5% to the blue population increase.

Abstract

We present the evolution of the color-magnitude distribution of galaxy clusters from z = 0.45 to z = 0.9 using a homogeneously selected sample of ~1000 clusters drawn from the Red-Sequence Cluster Survey (RCS). The red fraction of galaxies decreases as a function of increasing redshift for all cluster-centric radii, consistent with the Butcher-Oemler effect, and suggesting that the cluster blue population may be identified with newly infalling galaxies. We also find that the red fraction at the core has a shallower evolution compared with that at the cluster outskirts. Detailed examination of the color distribution of blue galaxies suggests that they have colors consistent with normal spirals and may redden slightly with time. Galaxies of starburst spectral type contribute less than 5% of the increase in the blue population at high redshift, implying that the observed Butcher-Oemler effect is not caused by a unobscured starbursts, but is more consistent with a normal coeval field population.