The evolution of the red sequence slope in massive galaxy clusters

TL;DR

This study examines how the slope of the red sequence in massive galaxy clusters changes over time from redshift 1 to the present, revealing evolution not fully captured by current models and showing an increase in faint red galaxies.

Contribution

It provides observational evidence of red sequence slope evolution in galaxy clusters and compares it with semi-analytic model predictions, highlighting discrepancies.

Findings

Red sequence slope evolves with redshift.

No strong correlation between slope and cluster environment.

Significant increase in faint red galaxies since z=0.5.

Abstract

We investigate the evolution of the optical and near-infrared colour-magnitude relation in an homogeneous sample of massive clusters from z = 1 to the present epoch. By comparing deep Hubble Space Telescope ACS imaging of X-ray selected MACS survey clusters at z = 0.5 to the similarly selected LARCS sample at z = 0.1 we find that the rest-frame d(U -V)/dV slope of the colour-magnitude relation evolves with redshift which we attribute to the build up of the red sequence over time. This rest frame slope evolution is not adequately reproduced by that predicted from semi-analytic models based on the Millennium Simulation despite a prescription for the build up of the red sequence by in-falling galaxies, 'strangulation'. We observe no strong correlation between this slope and the cluster environment at a given redshift demonstrating that the observed evolution is not due to a secondary correlation. Also presented are near-infrared UKIRT WFCAM observations of the LARCS clusters which confirm and improve on the the result from Stott et al. (2007) finding that there has been a two-fold increase in faint MV > -20 galaxies on the red sequence since z = 0.5 to a significance of 5sigma.