The z=1.03 Merging Cluster SPT-CL J0356-5337: New Strong Lensing Analysis with HST and MUSE

TL;DR

This study provides a detailed strong lensing analysis of the z=1.034 galaxy cluster SPT-CL J0356-5337 using new HST and MUSE data, revealing its mass distribution, multiple lensed sources, and evidence of a major merger.

Contribution

It introduces a more comprehensive lensing model with additional lensed sources and cluster members, improving mass estimates and understanding of the cluster's merging state.

Findings

Identified 12 sets of multiple images from 5 sources.

Measured redshifts of new lensed galaxies at z=3.0205 and z=5.3288.

Confirmed the cluster's major merger with two dominant mass components.

Abstract

We present a strong lensing analysis and reconstruct the mass distribution of SPT-CL J0356-5337, a galaxy cluster at redshift z = 1.034. Our model supersedes previous models by making use of new multi-band HST data and MUSE spectroscopy. We identify two additional lensed galaxies to inform a more well-constrained model using 12 sets of multiple images in 5 separate lensed sources. The three previously-known sources were spectroscopically confirmed by Mahler et al. (2020) at redshifts of z = 2.363, z = 2.364, and z = 3.048. We measured the spectroscopic redshifts of two of the newly-discovered arcs using MUSE data, at z = 3.0205 and z = 5.3288. We increase the number of cluster member galaxies by a factor of three compared to previous work. We also report the detection of extended Lya emission from several background galaxies. We measure the total projected mass density of the two major sub-cluster components, one dominated by the BCG, and the other by a compact group of luminous red galaxies. We find M_BCG(< 80kpc) = 3.93+0.21-0.14 * 10^13Msun and M_LRG(< 80kpc) = 2.92+0.16 -0.23 * 10^13Msun, yielding a mass ratio of 1.35+0.16 -0.08. The strong lensing constraints offer a robust estimate of the projected mass density regardless of modelling assumptions; allowing more substructure in this line of sight does not change the results or conclusions. Our results corroborate the conclusion that SPT-CL J0356-5337 is dominated by two mass components, and is likely undergoing a major merger on the plane of the sky