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

Abstract Although the James Webb Space Telescope 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 from the PLCK G165.7+67.0 (G165; z = 0.35) cluster, revealing a population of unresolved pointlike sources including globular clusters (GCs). By applying a fitting algorithm in color space used to select galaxy cluster members, we uncover over 900 GC 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 ± 83 GC candidates. We find the color-selected sources to be approximately spatially correlated 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 in the range −9.4 mag ≤ M F200W ≤ −10.7 mag, although we predict the expected k -corrected turnover point should be closer to −7.7 mag ≤ M F200W ≤ −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.