Differences between the globular cluster systems of the Virgo and Fornax Galaxy Clusters

TL;DR

This study compares globular cluster systems in the Virgo and Fornax galaxy clusters, revealing significant differences in their properties and associated low-mass X-ray binaries, indicating variations at the galaxy cluster scale.

Contribution

It provides a detailed comparison of globular cluster systems across two galaxy clusters using uniform optical and X-ray data, highlighting differences beyond individual galaxies.

Findings

Greater spread in luminosities and sizes in Virgo clusters

Different ratios of half-light radii across filters

Distinct distributions of low-mass X-ray binaries

Abstract

It is well known that Globular cluster systems are different among galaxies. Here we test to which degree these differences remain on the scale of galaxy clusters by comparing the globular clusters (GCs) in optical surveys of the Virgo galaxy cluster (ACSVCS) and the Fornax galaxy cluster (ACSFCS) in Kolmogorov-Smirnoff Tests. Both surveys were obtained with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope, and contain thousands of GCs in dozens of galaxies each. Also well over 100 point sources in the Chandra X-ray Observatory source catalogue were attributed to the GCs in both optical catalogues, and interpreted as low-mass X-ray binaries (LMXBs). Thus, the optical and X-ray data are as uniform as possible. Our main findings are as follows: (1) The spread in luminosities and half-light radii is larger in the ACSVCS than in the ACSFCS. (2) The ratio between the half-light radii for the F475W-passband and the F850LP-passband is on average smaller in the ACSVCS. (3) The distribution of the LMXBs with the luminosity of the GCs is different between both surveys. These findings are significant. The first finding could be a consequence of a wider spread in the distances of the GCs in the ACSVCS, but the others must have internal reasons in the GCs. Thus, the GC systems are also different on a galaxy cluster scale.