James Webb Space Telescope Feed Post

JWST Photometry of Globular Cluster Populations in Abell 2744 at z=0.3

A small portion of the A2744 mosaic field shown at very high contrast, at a location between two of the major galaxies. The field shown is 25'' across, equivalent to 200 kpc linear distance. The many small starlike objects indicate some of the globular clusters. The many thin short arcs crossing the center are strongly lensed background galaxies. Abstract: JWST imaging of the rich galaxy cluster Abell 2744 at z=0.308 has been used by the UNCOVER team (Bezanson et al. 2022) to construct mosaic images in the NIRCAM filters. The exceptionally deep images in the (F115W, F150W, F200W) bands reveal a large population of unresolved pointlike sources across the field, the vast majority of which are globular clusters (GCs). To the limits of our photometry, more than 10,000 such objects were measured, most of which are in the halos of the five largest A2744 galaxies but which also include GCs around some satellite galaxies and throughout the IntraCluster Medium. Their luminosity function follows a lognormal shape, with the data reaching to within one magnitude of the classic GCLF turnover point. The colour index (F115W-F200W) in particular covers a range of 0.5 mag, clearly resolving the expected internal spread of GC metallicities. The estimated GC masses are systematically higher than in present-day galaxies, consistent with a large, normal GC population seen at a 3.5 Gyr earlier stage of dynamical evolution. Lastly, the spatial distribution of the bluer (more metal-poor) GCs resembles the gravitational lensing map of the cluster, consistent with recent theoretical suggestions.