Mature but Still Growing: JWST Detection of the Earliest Intracluster Light at z ~ 2

TL;DR

This study uses JWST imaging to detect and analyze intracluster light at redshift ~2, revealing early formation stages of ICL in a distant galaxy cluster and its implications for cluster evolution.

Contribution

First detection and detailed analysis of intracluster light at z ~ 2, demonstrating early buildup of ICL in massive galaxy clusters.

Findings

ICL fraction is about 17% at z ~ 2

ICL shows minimal radial stellar population variation

System is dynamically active with ICL excess

Abstract

We present a JWST analysis of intracluster light (ICL) in XLSSC 122 at z = 1.98, currently the most distant known strong lensing galaxy cluster with an evolved member population. Using deep JWST imaging complemented by HST data and careful control of systematics, we robustly detect diffuse emission extending to several hundred kpc from the brightest cluster galaxy (BCG) down to about 29 mag arcsec^-2. Multi component PSF convolved Sersic modeling separates the surface brightness profiles into three components: a BCG core, a BCG envelope, and an ICL component, with stable Sersic indices across wavelengths. Nearly flat color profiles indicate minimal radial variation in the stellar populations of the BCG envelope and the ICL. The median ICL fraction measured across seven bands is about 17 percent, demonstrating that the buildup of intracluster stars in massive halos was already well underway by z about 2. The ICL fraction peaks near 5000 Angstrom in the rest frame, resembling the behavior observed in dynamically active clusters. We also detect a southern excess of ICL relative to the best fit Sersic model and quantify it using wavelet based modeling, providing additional support that this system is dynamically active. The BCG + ICL light distribution and strong lensing mass map show strong morphological agreement within about 100 kpc. These findings establish the ICL as an early forming and dynamically informative component of massive halos.