Globular Clusters, Ultracompact Dwarfs, and Dwarf Galaxies in Abell 2744 at the Redshift of 0.308

TL;DR

This study analyzes the populations of globular clusters, ultracompact dwarfs, and dwarf galaxies in Abell 2744 at z=0.308, revealing their luminosity functions, spatial distributions, and implications for their origins.

Contribution

It provides the first detailed photometric analysis of UCDs and GCs in Abell 2744 at intermediate redshift, supporting the galaxy-origin scenario for bright UCDs.

Findings

Estimated 385,000 GCs and 147 UCDs in Abell 2744.

Luminosity function shows a break at M_r' ~ -12.9 mag.

UCDs have similar radial profiles to bright GCs, steeper than dwarf galaxies.

Abstract

We report a photometric study of globular clusters (GCs), ultracompact dwarfs (UCDs), and dwarf galaxies in the giant merging galaxy cluster Abell 2744 at z = 0.308. Color-magnitude diagrams of the point sources derived from deep F814W (restframe r') and F105W (restframe I) images of Abell 2744 in the Hubble Space Telescope Frontier Field show a rich population of point sources whose colors are similar to those of typical GCs. These sources are as bright as -14.9 < M_r' < -11.4 (26.0 < F814W < 29.5) mag, being mostly UCDs and bright GCs in Abell 2744. The luminosity function (LF) of these sources shows a break at M_r' ~ -12.9 (F814W ~ 28.0) mag, indicating a boundary between UCDs and bright GCs. The numbers of GCs and UCDs are estimated to be N_GC = 385,000+-24,000, and 147 +- 26, respectively. The clustercentric radial number density profiles of the UCDs and bright GCs show similar slopes, but these profiles are much steeper than that of the dwarf galaxies and the mass density profile based on gravitational lensing analysis. We derive an LF of the red sequence galaxies for -22.9 < M_r' < -13.9 mag. The faint end of this LF is fit well by a flat power law with a = -1.14 +- 0.08, showing no faint upturn. These results support the galaxy-origin scenario for bright UCDs: they are the nuclei of dwarf galaxies that were stripped when they pass close to the center of massive galaxies or a galaxy cluster, while some of the faint UCDs are the bright end of the GCs.