Comparing Globular Cluster System Properties with Host Galaxy Environment

TL;DR

This study analyzes globular cluster systems in 15 massive elliptical galaxies using Hubble data to explore how their properties relate to galaxy environment, finding minimal correlation except for a weak link with local density.

Contribution

It provides a detailed comparison of globular cluster metallicity distributions across different galaxy environments using new photometric data and a model relating colour to metallicity.

Findings

Weak correlation between blue fraction and local density.

GC system properties are more influenced by early local environment.

Minimal correlation between GCS properties and current galaxy environment.

Abstract

We present Hubble Space Telescope photometry in optical (F475X) and near-infrared (F110W) bands of the globular cluster (GC) systems of the inner halos of a sample of 15 massive elliptical galaxies. The targets are selected from the volume-limited MASSIVE survey, and chosen to sample a range of environments from sparsely populated groups to BCGs in dense clusters. We also present a quantitative model of the relation between (F475X - F110W) colour and cluster metallicity [M/H], using simulated GCs. Because much of the GC population in such galaxies is built up through accretion, the metallicity distribution of the GC systems might be expected to vary with galaxy environment. The photometry is used to create a completeness-corrected metallicity distribution for each galaxy in the sample, and to fit a double Gaussian curve to each histogram in order to model the two standard red and blue subpopulations. Finally, the properties of the GC metallicity distribution are correlated against galaxy environment. We find that almost no GCS properties and host galaxy environmental properties are correlated, with the exception of a weak but consistent correlation between blue fraction and nth-nearest neighbour surface density. The results suggest that the systemic properties of the GCS, at least in the inner to mid-halo regions, are influenced more strongly by the local environment at early times, rather than by the environmental properties we see today.