An Active Galaxy Cluster Merger at Cosmic Noon Revealed by JWST Weak Lensing and Multiwavelength Probes

TL;DR

This study uses JWST weak lensing and multiwavelength data to analyze a high-redshift galaxy cluster, revealing its mass distribution, merger activity, and demonstrating JWST's capability to study cluster assembly at cosmic noon.

Contribution

First weak-lensing mass reconstruction of a $z hickapprox 2$ galaxy cluster using JWST, combined with multiwavelength data to study its structure and merger activity.

Findings

Mass estimate of $1.6 imes 10^{14} M_\u200bod$ with high concentration.

Detected elongation and offsets indicating merger activity.

JWST effectively maps cluster mass at high redshift.

Abstract

The galaxy cluster XLSSC~122 is a rare system at $z = 1.98$, hosting surprisingly evolved member galaxies when the Universe was only one-third of its present age. Leveraging deep JWST/NIRCam imaging, we perform a weak-lensing analysis and reconstruct the cluster's mass distribution, finding a mass peak that coincides with both the X-ray peak and the position of the brightest cluster galaxy. We obtain a mass estimate of $M_{200\rm c}=1.6 \pm 0.3\times 10^{14}~M_{\odot}$ and a concentration of $c_{200 \rm c}=6.3 \pm 0.3$ implied by the preferred concentration--mass relation, in agreement with recent strong-lensing estimates. The high concentration in particular motivates tests against empirical and simulation-derived concentration--mass relations. Placing our weak-lensing mass map in the context of Chandra X-ray data, MeerKAT radio imaging, ALMA+ACA/ACT Sunyaev-Zel'dovich (SZ) mapping, and new JWST intracluster light measurements, we identify consistent NE--SW elongation across datasets and a pronounced offset along the same axis between the SZ and mass/X-ray peaks, pointing to significant merger activity. XLSSC~122 thus serves as a JWST pilot study for high-$z$ lensing, demonstrating the telescope's unique ability to map cluster mass distributions at $z\sim 2$ and motivating a uniform sample of analogous systems with joint lensing, X-ray, SZ, and radio data to probe cluster assembly at cosmic noon.