The Velocity Dispersion Function for Quiescent Galaxies in Nine Strong-lensing Clusters

Abstract

We measure the central stellar velocity dispersion function for quiescent galaxies in a set of nine northern clusters in the redshift range 0.18 <  z  < 0.29 and with strong lensing arcs in Hubble Space Telescope images. The velocity dispersion function links galaxies directly to their dark matter halos. From dense SDSS and MMT/Hectospec spectroscopy, we identify 222–463 spectroscopic members in each cluster. We derive physical properties of cluster members including redshift, , and central stellar velocity dispersion and we include a table of these measurements for 3419 cluster members. We construct the velocity dispersion functions for quiescent galaxies with  > 1.5 and within R 200 . The cluster velocity dispersion functions all show excesses at σ  ≳ 250 km s −1 compared to the field velocity dispersion function. The velocity dispersion function slope at large velocity dispersion ( σ  > 160 km s −1 ) is steeper for more massive clusters, consistent with the trend observed for cluster luminosity functions. The spatial distribution of galaxies with large velocity dispersion at radii larger than R 200 further underscores the probable major role of dry mergers in the growth of massive cluster galaxies during cluster assembly.