PEARLS: Globular Clusters and Ultra-Compact Dwarfs in the El Gordo Galaxies at z=0.87

TL;DR

This study uses JWST imaging to identify and analyze ultra-compact dwarf galaxies and globular clusters in the El Gordo cluster at z=0.87, revealing their properties and evolution over cosmic time.

Contribution

First identification and analysis of UCDs and GCs in a high-redshift cluster using JWST, demonstrating their luminosity evolution and potential for future observations.

Findings

UCDs and GCs are detected at z=0.87 with properties consistent with evolutionary models.

The luminosity of these systems is nearly a magnitude brighter than in lower-redshift clusters.

Future JWST observations could directly image these populations up to z ~ 1.4.

Abstract

JWST/NIRCam 0.9 to 2.0 micron images reveal a population of point sources around the major galaxies in the El Gordo cluster at redshift z=0.87. Their distribution in the color--magnitude diagrams shows a narrow sequence well separated from field-galaxy contamination and consistent with their identification as ultra-compact dwarf galaxies (UCDs) or luminous globular clusters (GCs). The point-source sequence is more luminous by almost a magnitude than the corresponding sequence in Abell 2744 at z=0.31, matching the predicted evolutionary change for GC/UCDs over the 4-Gyr difference in lookback time between these two clusters. Deeper observations should allow direct JWST imaging of GC/UCD populations, even without the help of lensing, up to z ~ 1.4, a lookback time of more than 9 Gyr. Such observations would directly reveal the evolution of these compact stellar systems two-thirds of the way back to the Big Bang.