Southern African Large Telescope observations of Sunyaev-Zel'dovich effect selected clusters from the Atacama Cosmology Telescope.

Abstract

We present Southern African Large Telescope (SALT) follow-up observations of seven massive clusters detected by the Atacama Cosmology Telescope (ACT) using the Sunyaev-Zel’dovich effect (SZE). We conducted multi-object spectroscopic observations with the Robert Stobie Spectrograph (RSS) in order to measure galaxy redshifts in each cluster field, determine the cluster line of sight velocity dispersions, and infer the cluster dynamical masses. This programme forms part of the larger ACT effort to measure the SZE-signal-to-mass relation using a mass proxy which is independent of cluster gas properties. While all of the clusters in this work have previously been identified in optical surveys within the Sloan Digital Sky Survey footprint, none of them have been studied in this way before. We find that the clusters range in mass from (0.26 - 2.6) 1015 M and span the redshift range 0.3 < z < 0.55. The spectrum of the Brightest Cluster Galaxy (BCG) in ACT-CL J0320.4+0032 shows strong emission line features indicating the presence of an Active Galactic Nucleus (AGN), potentially providing feedback within a very massive cluster.