On the role of the post-starburst phase in the build-up of the red-sequence of intermediate redshift clusters

TL;DR

This study investigates the role of post-starburst galaxies in forming the red sequence in intermediate-redshift clusters, finding their contribution is limited and suggesting other processes dominate galaxy transformation.

Contribution

It provides new deep spectroscopic data for faint galaxies in a z=0.54 cluster, challenging the significance of post-starburst galaxies in red sequence buildup.

Findings

Few post-starburst galaxies observed, insufficient to explain red sequence growth.

Post-starburst phase is not the main pathway for galaxy transformation in clusters.

Data exclude a large population of k+a galaxies at faint magnitudes.

Abstract

We present new deep spectroscopic observations of 0.05--0.5 L_* galaxies in one cluster (cl1232.5-1250) drawn from the ESO Distant Cluster Survey (EDisCS) sample, at z = 0.54. The new data extend the spectroscopy already available for this cluster by about 1 magnitude. The cluster has a large fraction of passive galaxies and exhibits a well defined and relatively tight colour-magnitude relation. Among spectroscopic members, only six galaxies are classified as `post-starburst' (k+a). For another EDisCS cluster at similar redshift and with as deep spectroscopy, no member is found to have a k+a spectrum. The low measured numbers of post-starburst systems appear to be inadequate to explain the observed increase of faint red galaxies at lower redshift, even when accounting for the infall of new galaxies onto the cluster. Post-starburst galaxies represent a possible channel to move galaxies from the blue star-forming cloud to the red-sequence, but the available data suggest this is not the dominant channel in galaxy clusters. If the galaxies at the faint end of the red-sequence in nearby clusters originate from the blue galaxies observed in distant galaxy clusters, the transformation must have occurred primarily through physical processes that do not lead to a post-starburst phase. In addition, our data exclude a large population of k+a galaxies at faint magnitudes, as found in the Coma cluster.