Hidden in Plain Sight: Searching for Globular Clusters Within JWST Observations of the PLCK G165.7+67.0 Galaxy Cluster

TL;DR

This study utilizes JWST observations to identify and analyze globular cluster candidates in the galaxy cluster PLCK G165.7+67.0, revealing over 900 candidates and exploring their spatial and luminosity properties in relation to the cluster's mass and structure.

Contribution

It introduces a novel methodology of subtracting intracluster light in JWST data to detect globular clusters within a galaxy cluster at z=0.35, providing new insights into their distribution and properties.

Findings

Over 900 globular cluster candidates identified.

Spatial correlation between GCs and cluster mass distribution.

Predicted luminosity function turnover points.

Abstract

Although the James Webb Space Telescope (JWST) has received much attention for its ability to search deeper into the cosmos than ever before, it also enhances our capability to study objects closer to us in the Universe. We apply a methodology of subtracting intracluster light to the PLCK G165.7+67.0 (G165; $z$ = 0.35) cluster, revealing a population of unresolved point-like sources including globular clusters (GCs). By applying a fitting algorithm in color space used to select galaxy cluster members, we uncover over 900 globular cluster candidates from our point source sample. We also identify candidates by estimating the contribution of interlopers to the point source sample, yielding an estimate of 793$\pm$ 83 globular cluster candidates. We find the color-selected sources to be approximately correlated spatially with the intracluster light and lensing mass of the cluster. The observed luminosity function of the sources shows a turnover point fainter than the completeness limit, so we use fixed-parameter curve fitting models to predict a K-corrected turnover point between $-9.4 \leq M_{\rm F200W} \leq -10.7$ mag, although we predict the expected K-corrected turnover point should be closer to $-7.7 \leq M_{\rm F200W} \leq -8.4$ mag. We discuss the dynamical state of this disturbed galaxy cluster with a bimodal mass distribution using the spatial distribution of GC candidates and find that the radial profiles of our color-selected GC candidates are very consistent with the lensing-derived surface mass density at $>$50 kpc.