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

TL;DR

This study measures the velocity dispersion function of quiescent galaxies in nine galaxy clusters, revealing excesses at high dispersions and suggesting dry mergers play a key role in galaxy growth during cluster assembly.

Contribution

It provides the first detailed velocity dispersion functions for quiescent galaxies in multiple clusters at intermediate redshift, linking galaxy dynamics to dark matter halos and cluster evolution.

Findings

Excess of high-velocity dispersion galaxies compared to the field.

Steeper velocity dispersion function slopes in more massive clusters.

Evidence of dry mergers influencing galaxy growth beyond cluster cores.

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 $231 - 479$ spectroscopic members in each cluster. We derive physical properties of cluster members including redshift, $D_{n}4000$, 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 $D_{n}4000 > 1.5$ and within $R_{200}$. The cluster velocity dispersion functions all show excesses at $\sigma \gtrsim 250 km s^{-1}$ compared to the field velocity dispersion function. The velocity dispersion function slope at large velocity dispersion ($\sigma > 160 km s^{-1}$) 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.