Probing Galaxy Cluster Dynamics: Virial Mass Constraints and Velocity Phase-Space Substructure Analysis

Galaxy clusters are the largest gravitationally bound structures in the universe, and provide important insights into many fundamental properties of the universe and its evolutionary trajectory. We analyze a sample of galaxy clusters that span the redshift range 0.16 < z < 0.6, all of which are selected based on their strong lensing features and published strong lensing models that offer precise mass constraints in their cores. Understanding the overall matter distributions within these clusters requires constraining the cluster virial masses, estimated from observed velocity distributions of galaxies navigating the gravitational potential of each cluster. Virial mass constraints are highly complementary to the existing core mass constraints from the published strong lensing models. We present new spectroscopic measurements for ~900 galaxies in the fields around 8 strong lensing galaxy clusters, resulting in hundreds of new cluster member redshifts which we combine with existing redshift catalogs from the literature. We utilize robust bi-weight estimators to derive the cosmological redshifts and cluster member velocity dispersions for our strong lensing cluster sample, and we use the velocity dispersions to estimate the total cluster virial masses using published scaling relations. We also use the cluster member redshift measurements to measure velocity phase-space substructure within galaxy clusters; a key tool for probing the merger histories of these clusters. This approach provides insights into the virialization of galaxies within the overall cluster potential, shedding light on recent merging events and their impact on the dynamics of member galaxies. The presence or absence of phase-space substructure informs us about the cluster's level of disturbance, distinguishing between recently merged ("disturbed") and fully virialized (""relaxed") clusters.