VLT/Magellan spectroscopy of 29 strong lensing selected galaxy clusters

TL;DR

This study provides spectroscopic redshifts and dynamical mass estimates for 29 strong lensing galaxy clusters, enhancing understanding of their properties and potential biases in mass measurements.

Contribution

It offers a comprehensive spectroscopic follow-up of a large sample of strong lensing clusters, including background source redshifts and dynamical mass estimates, with analysis of possible biases.

Findings

Redshifts for 52 gravitational arcs from 35 sources spanning $0.8 \,\le\, z \le\, 2.9$.

Velocity dispersions measured for 23 clusters, enabling dynamical mass estimates.

Identification of substructure in some clusters, with most velocity distributions being unimodal.

Abstract

We present an extensive spectroscopic follow-up campaign of 29 strong lensing (SL) selected galaxy clusters discovered primarily in the Second Red-Sequence Cluster Survey (RCS-2). Our spectroscopic analysis yields redshifts for 52 gravitational arcs present in the core of our galaxy clusters, which correspond to 35 distinct background sources that are clearly distorted by the gravitational potential of these clusters. These lensed galaxies span a wide redshift range of $0.8 \le z \le 2.9$, with a median redshift of $z_s = 1.8 \pm 0.1 $. We also measure reliable redshifts for 1004 cluster members, allowing us to obtain robust velocity dispersion measurements for 23 of these clusters, which we then use to determine their dynamical masses by using a simulation-based $\sigma_{DM} - M_{200}$ scaling relation. The redshift and mass ranges covered by our SL sample are $0.22 \le z \le 1.01$ and $5 \times10^{13} \le M_{200}/h^{-1}_{70}M_{\odot} \le 1.9\times10^{15}$, respectively. We analyze and quantify some possible effects that might bias our mass estimates, such as the presence of substructure, the region where cluster members are selected for spectroscopic follow-up, the final number of confirmed members, and line-of-sight effects. We find that 10 clusters of our sample with $N_{mem} \gtrsim 20$ show signs of dynamical substructure. However, the velocity data of only one system is inconsistent with a uni-modal distribution. We therefore assume that the substructures are only marginal and not of comparable size to the clusters themselves. Consequently, our velocity dispersion and mass estimates can be used as priors for SL mass reconstruction studies and also represent an important step toward a better understanding of the properties of the SL galaxy cluster population.