Globular cluster systems in fossil groups: NGC6482, NGC1132 and ESO306-017

TL;DR

This study systematically analyzes globular cluster systems in three fossil group galaxies, revealing common features like bimodal color distributions and extended spatial profiles, and finds correlations with galaxy luminosity and X-ray properties.

Contribution

First comprehensive analysis of GC systems in fossil groups, highlighting their properties and relationships with galaxy and X-ray characteristics.

Findings

GC color distribution is bimodal in all three systems.

GCs are more extended than the galaxy starlight.

Specific frequencies are similar to those in bright ellipticals.

Abstract

We study the globular cluster (GC) systems in three representative fossil group galaxies: the nearest (NGC6482), the prototype (NGC1132) and the most massive known to date (ESO306-017). This is the first systematic study of GC systems in fossil groups. Using data obtained with the Hubble Space Telescope Advanced Camera for Surveys in the F475W and F850LP filters, we determine the GC color and magnitude distributions, surface number density profiles, and specific frequencies. In all three systems, the GC color distribution is bimodal, the GCs are spatially more extended than the starlight, and the red population is more concentrated than the blue. The specific frequencies seem to scale with the optical luminosities of the central galaxy and span a range similar to that of the normal bright elliptical galaxies in rich environments. We also analyze the galaxy surface brightness distributions to look for deviations from the best-fit S\'ersic profiles; we find evidence of recent dynamical interaction in all three fossil group galaxies. Using X-ray data from the literature, we find that luminosity and metallicity appear to correlate with the number of GCs and their mean color, respectively. Interestingly, although NGC6482 has the lowest mass and luminosity in our sample, its GC system has the reddest mean color, and the surrounding X-ray gas has the highest metallicity.