Globular Cluster Populations in Four Early-Type Poststarburst Galaxies

TL;DR

This study investigates globular cluster systems in four early-type poststarburst galaxies, revealing evidence of intermediate-age clusters formed during mergers, contrasting with typical old, metal-rich populations.

Contribution

It provides new insights into the age and metallicity distributions of globular clusters in poststarburst galaxies, highlighting merger-induced cluster formation.

Findings

Evidence of intermediate-age (~1 Gyr) globular clusters in three galaxies

Presence of young (~500 Myr) clusters likely formed during mergers

Absence of old, metal-rich red cluster populations in the sample

Abstract

We present a study of the globular cluster systems of four early-type poststarburst galaxies using deep g and I-band images from the ACS camera aboard the Hubble Space Telescope (HST). All the galaxies feature shells distributed around their main bodies and are thus likely merger remnants. The color distribution of the globular clusters in all four galaxies shows a broad peak centered on g-I ~ 1.4, while PGC 6240 and PGC 42871 show a significant number of globular clusters with g-I ~ 1.0. The latter globular clusters are interpreted as being of age ~ 500 Myr and likely having been formed in the merger. The color of the redder peak is consistent with that expected for an old metal-poor population that is very commonly found around normal galaxies. However, all galaxies except PGC 10922 contain several globular clusters that are significantly brighter than the maximum luminosity expected of a single old metal-poor population. To test for multiple-age populations of overlapping g-I color, we model the luminosity functions of the globular clusters as composites of an old metal-poor subpopulation with a range of plausible specific frequencies and an intermediate-age subpopulation of solar metallicity. We find that three of the four sample galaxies show evidence for the presence of an intermediate-age (~ 1 Gyr) globular cluster population, in addition to the old metal-poor GC population seen in normal early-type galaxies. None of the galaxies show a significant population of clusters consistent with an old, metal-rich red cluster population that is typically seen in early-type galaxies.