Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

JWST Discovery of Strong Lensing from a Galaxy Cluster at Cosmic Noon: Giant Arcs and a Highly Concentrated Core of XLSSC 122

Kyle Finner, Sangjun Cha, Zachary P. Scofield, M. James Jee, Yu-heng Lin, Hyungjin Joo, Hyosun Park, Takahiro Morishita, Andreas Faisst, Bomee Lee, Wuji Wang, Ranga-Ram Chary

TL;DR

This study presents JWST/NIRCam imaging of the galaxy cluster XLSSC 122 at $z=1.98$, revealing giant strong-lensing arcs and enabling a robust strong-lensing mass analysis of the cluster core. Using Lenstronomy with nine cluster galaxies plus a central BCG halo, the authors derive a convergence map and radial mass-density profile out to 100 kpc, obtaining a remarkably high concentration of $c=6.3\pm0.5$ and a core mass of $M(R<100\text{kpc})=6.5\pm0.7\times10^{13}\,M_\odot$, with $M_{200c}=2.6\pm1.1\times10^{14}\,M_\odot$. These values exceed predictions from standard mass–concentration relations, implying accelerated early halo assembly or alternative cosmologies; additional evidence from multiwavelength data suggests a plane-of-sky elongated mass distribution rather than a LOS effect. The results, consistent with other cluster probes, highlight the potential for rapid structure formation in the early universe and motivate follow-up weak-lensing analyses to refine the total mass and geometry of XLSSC 122.

Abstract

Our observations with the James Webb Space Telescope have made the remarkable discovery of strong gravitational lensing arcs from XLSSC 122 ($z=1.98$) - setting the record for the most distant galaxy cluster that exhibits strong lensing. The discovery of giant arcs enables a strong-lensing analysis and a measurement of the concentration of the dark matter halo. We perform a strong-lensing analysis of the cluster and measure the radial projected mass density profile. Our measurements reveal an exceptionally high concentration in the core of XLSSC 122. A Navarro--Frenk--White profile fit to the inner 100 kpc estimates the concentration to be $6.3\pm0.5$. The high concentration of XLSSC 122 contributes to the emerging picture that massive structure formation in the early universe may proceed more rapidly than standard models suggest. We estimate the mass within 100 kpc to be $M$($R<$100 kpc) = $6.5\pm0.7\times10^{13}$ M$_\odot$. Our mosaic images are made public at https://kylefinner.github.io/xlssc122 .

JWST Discovery of Strong Lensing from a Galaxy Cluster at Cosmic Noon: Giant Arcs and a Highly Concentrated Core of XLSSC 122

TL;DR

This study presents JWST/NIRCam imaging of the galaxy cluster XLSSC 122 at , revealing giant strong-lensing arcs and enabling a robust strong-lensing mass analysis of the cluster core. Using Lenstronomy with nine cluster galaxies plus a central BCG halo, the authors derive a convergence map and radial mass-density profile out to 100 kpc, obtaining a remarkably high concentration of and a core mass of , with . These values exceed predictions from standard mass–concentration relations, implying accelerated early halo assembly or alternative cosmologies; additional evidence from multiwavelength data suggests a plane-of-sky elongated mass distribution rather than a LOS effect. The results, consistent with other cluster probes, highlight the potential for rapid structure formation in the early universe and motivate follow-up weak-lensing analyses to refine the total mass and geometry of XLSSC 122.

Abstract

Our observations with the James Webb Space Telescope have made the remarkable discovery of strong gravitational lensing arcs from XLSSC 122 () - setting the record for the most distant galaxy cluster that exhibits strong lensing. The discovery of giant arcs enables a strong-lensing analysis and a measurement of the concentration of the dark matter halo. We perform a strong-lensing analysis of the cluster and measure the radial projected mass density profile. Our measurements reveal an exceptionally high concentration in the core of XLSSC 122. A Navarro--Frenk--White profile fit to the inner 100 kpc estimates the concentration to be . The high concentration of XLSSC 122 contributes to the emerging picture that massive structure formation in the early universe may proceed more rapidly than standard models suggest. We estimate the mass within 100 kpc to be (100 kpc) = M. Our mosaic images are made public at https://kylefinner.github.io/xlssc122 .

Paper Structure

This paper contains 10 sections, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Observations and Data Reduction
  3. Strong-Lensing Images and Analysis
  4. Results
  5. Radial Projected Mass Density
  6. Discussion
  7. High Concentration
  8. Rarity
  9. Conclusions
  10. Software and third party data repository citations

Figures (4)

  • Figure 1: The left panels show the color-composite image (top) and denoised color-composite image (bottom) of the core of galaxy cluster XLSSC 122 with RGB colors from F356W, F200W+F277W, and F090W, respectively. The denoised image was produced using a Transformer-based reconstruction method 2024park2025scofield. The middle and right panels show the log-scale, single-filter images as labeled. The cluster galaxies are much fainter in the F090W filter because, at $z = 1.98$, the filter probes rest-frame wavelengths below the 4000 Å break. The strong-lensing arcs are labeled with purple arrows in the top-right image and are visible in all filters. The intracluster light is prominent in the redder filters and stretches from the BCG to the southeast H. Joo et al. (in prep.).
  • Figure 2: Galaxy cluster mass as a function of redshift for the SPT, ACT, and Planck surveys (open circles). Filled circles mark the galaxy clusters that have strong-lensing analyses from the CLASH, HFF, RELICS, and SLICE surveys. The black dashed line is the 95% full-sky exclusion curve that separates expected (below) versus unexpected (above) cluster masses in the Universe. XLSSC 122 (mass from ACT) straddles the exclusions curve and sits at a substantially higher redshift than the galaxy clusters in the previous strong-lensing surveys.
  • Figure 3: Left: Our parametric strong-lensing convergence map (magenta contours) overplotted on the color image of XLSSC 122. Right: Strong-lensing critical curves (cyan contours) for a source at $z=3.8$ plotted over the denoised color image. Multiple-image groups are marked with open circles and labeled with their identifier.
  • Figure 4: Radial mass density profile (black circles) from the strong-lensing model with best-fit NFW relation (black curve). Mass-concentration relations (dashed curves) from literature are fit to the radial profile. The mass-concentration relations are unable to reproduce the radial profile of XLSSC 122, cause an over-estimation of the mass, and an under-estimation of the concentration. Masses are reported in units of $10^{14}$ M$_\odot$. Reduced chi-square $\chi_\nu^2$ are presented for each model.