Globular Cluster System Properties by Host Galaxy Environment

Abstract

I present Hubble Space Telescope photometry in optical (F475X, 475 nm) and near-infrared (F110W, 1.1 μm) bands of the globular cluster (GC) system of the inner haloes of a sample of 15 brightest cluster galaxies (BCGs). I also present a quantitative model of the relation between (F475X - F110W) colour and cluster metallicity, using simulated GCs. The sample comprises massive elliptical galaxies in a range of environments, from sparsely populated groups to dense clusters. Because the material available for large galaxies to accrete varies with environment and GC systems of such galaxies are built up through accretion, I expect the metallicity distribution of the GC systems in my sample to vary with galaxy environment. GC systems in massive elliptical galaxies tend to follow a bimodal colour distribution, with two subpopulations of blue (metal-poor) and red (metal-rich) clusters. The photometry is used to create a completeness-corrected metallicity histogram for each galaxy in my sample, and to fit a double Gaussian curve to each histogram in order to model the two subpopulations. Finally, the properties of the GC metallicity distribution are correlated against each BCG environment. I found that almost no GCS properties and host galaxy environmental properties are correlated, with the exception of weak but consistent correlations between number of GCs and nth-nearest neighbour surface density and between blue fraction and nth-nearest neighbour surface density.