RELICS: A Strong Lens Model for SPT-CLJ0615-5746, a z=0.972 Cluster

TL;DR

This paper presents a detailed strong lens model for the high-redshift galaxy cluster SPT-CLJ0615-5746 at z=0.972, identifying multiple lensed systems and estimating its mass distribution, which aligns with other mass measurements.

Contribution

The first full strong lens model for the highest redshift cluster in the RELICS survey, incorporating spectroscopic confirmations and complex mass modeling.

Findings

Identified three multiply-imaged systems, two spectroscopically confirmed.

Estimated the cluster's mass within the strong lensing region as ~2.5 x 10^{14} solar masses.

Model consistency with weak lensing and Sunyaev-Zel'dovich effect measurements.

Abstract

We present a lens model for the cluster SPT-CLJ0615$-$5746, which is the highest redshift ($z=0.972$) system in the Reionization of Lensing Clusters Survey (RELICS), making it the highest redshift cluster for which a full strong lens model is published. We identify three systems of multiply-imaged lensed galaxies, two of which we spectroscopically confirm at $z=1.358$ and $z=4.013$, which we use as constraints for the model. We find a foreground structure at $z\sim0.4$, which we include as a second cluster-sized halo in one of our models; however two different statistical tests find the best-fit model consists of one cluster-sized halo combined with three individually optimized galaxy-sized halos, as well as contributions from the cluster galaxies themselves. We find the total projected mass density within $r=26.7"$ (the region where the strong lensing constraints exist) to be $M=2.51^{+0.15}_{-0.09}\times 10^{14}$~M$_{\odot}$. If we extrapolate out to $r_{500}$, our projected mass density is consistent with the mass inferred from weak lensing and from the Sunyaev-Zel'dovich effect ($M\sim10^{15}$~M$_{\odot}$). This cluster is lensing a previously reported $z\sim10$ galaxy, which, if spectroscopically confirmed, will be the highest-redshift strongly lensed galaxy known.