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

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 mass and concentration estimates of $M_{200\rm c}=1.6 \pm 0.3\times 10^{14}~M_{\odot}$ and $c_{200 \rm c}=6.3 \pm 0.3$, respectively, in agreement with recent strong-lensing estimates. The high concentration in particular motivates tests against empirical and simulation-derived mass--concentration 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 a new JWST intracluster light measurement, 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 $z\sim2$ and motivating a uniform sample of analogous systems with joint lensing, X-ray, SZ, and radio data to probe cluster assembly at Cosmic Noon.