Detection of Intracluster Globular Clusters in the First JWST Images of the Gravitational Lens Cluster SMACS J0723.3–7327 at z = 0.39

Abstract

We present a survey of globular clusters (GCs) in the massive gravitational lens cluster SMACS J0723.3–7327 at z = 0.39 based on the early released JWST/NIRCam images. In the color–magnitude diagrams of the point sources, we clearly find a rich population of intracluster GCs that are spread over a wide area of the cluster. Their ages, considering the cluster redshift, are younger than 9.5 Gyr. The F200W (AB) magnitudes of these GCs, 26.5 mag < F200W0 < 29.5 mag, correspond to −15.2 mag < M F200W < −12.2 mag, showing that they belong to the brightest GCs (including ultracompact dwarfs). The spatial distributions of these GCs show a megaparsec-scale structure elongated along the major axis of the brightest cluster galaxy. In addition, they show a large number of substructures, some of which are consistent with the substructures seen in the map of diffuse intracluster light. The GC number density map is, in general, consistent with the dark matter mass density map based on the strong lensing analysis in the literature. The radial number density profile of the GCs in the outer region is steeper than the dark matter mass profile obtained from lensing models. These results are consistent with those for the GCs found in the deep HST images of A2744, another massive cluster at z = 0.308, and in simulated galaxy clusters. This shows that the intracluster GCs are an excellent independent tool to probe the dark matter distribution in galaxy clusters, as well as reveal the cluster assembly history in the JWST era.