Globular Cluster Systems in Brightest Cluster Galaxies: Further Definition of the Mass-Metallicity Relation

Abstract

<p> Globular clusters (GCs) can be divided into two subpopulations when plotted on a colour-magnitude diagram: one red and metal-rich (MR), and the other blue and metal-poor (MP). For each subpopulation, any correlation between colour and luminosity can then be converted into mass-metallicity relations (MMRs).</p> <p> Tracing the MMRs for fifteen GC systems (GCSs) - all around Brightest Cluster Galaxies - we see a nonzero trend for the MP subpopulation but not the MR. This trend is characterised by p in the relation Z=M^p. We find p ~ 0.35 for the MP GCs, and a relation for the MR GCs that is consistent with zero. When we look at how this trend varies with the host galaxy luminosity, we extend previous studies (e.g., Mieske et al, 2006b) into the bright end of the host galaxy sample.</p> <p> In addition to previously presented (B-I) photometry for eight GCSs obtained with ACS/WFC on the HST, we present seven more GCSs. Four of these are newly analysed from HST data, one is previously presented (g-i) photometry obtained with GMOS on Gemini South, and two are the author's newly reduced and analysed (g-i) photometry also obtained with GMOS on Gemini South.</p> <p> Interpretation of these results is important for further understanding the formation and evolution of galaxies within the hierarchical-merging picture, and what process enables the production of two subpopulations.</p>