The Velocity Dispersion Function of Very Massive Galaxy Clusters: Abell 2029 and Coma

TL;DR

This study measures and compares the velocity dispersion functions of galaxy clusters Abell 2029 and Coma, revealing significant differences from field galaxies that inform models of cosmic structure formation.

Contribution

It provides the first detailed measurements of VDFs for these clusters and compares them to field galaxies, offering new insights into galaxy evolution in dense environments.

Findings

Cluster VDFs are steeper than field VDFs for low velocity dispersions.

Cluster VDFs exceed field VDFs at high velocity dispersions.

SMFs of clusters align with simulation predictions.

Abstract

Based on an extensive redshift survey for galaxy cluster Abell 2029 and Coma, we measure the luminosity functions (LFs), stellar mass functions (SMFs) for the entire cluster member galaxies. Most importantly, we measure the velocity dispersion functions (VDFs) for quiescent members. The MMT/Hectospec redshift survey for galaxies in A2029 identifies 982 spectroscopic members; for 838 members we derive the central velocity dispersion from the spectroscopy. Coma is the only other cluster surveyed as densely. The LFs, SMFs and VDFs for A2029 and Coma are essentially identical. The SMFs of the clusters are consistent with simulations. The A2029 and Coma VDFs for quiescent galaxies have a significantly steeper slope than those of field galaxies for velocity dispersion $\lesssim 100$ km s$^{-1}$. The cluster VDFs also exceed the field at velocity dispersion $\gtrsim 250$ km s$^{-1}$. The differences between cluster and field VDFs are potentially important tests of simulations and of the formation of structure in the universe.