Ellipticals with Kinematically--Distinct Cores: WFPC2 Imaging of Globular Clusters

Abstract

Here we present HST WFPC2 imaging of 14 kinematically--distinct core ellipticals to examine their globular cluster systems. In particular, we probe the galaxy central regions, for which we might expect to see the strongest signatures of some formation and destruction processes. These data substantially increase the number of extragalactic globular cluster systems studied to date. We find that the globular cluster luminosity, and color, vary only weakly, if at all, with galactocentric distance. The mean color of globular clusters are constant with globular cluster magnitude. Several clear trends are also present. Firstly, globular cluster colors are bluer (more metal poor by ~ 0.5 dex) than the underlying galaxy starlight at any given galactocentric distance. Second, we find a correlation over roughly ten magnitudes between the mean globular cluster metallicity and parent galaxy luminosity of the form Z goes as L^0.4. This relationship includes dwarf ellipticals, spiral galaxy bulges and giant ellipticals. Third, we find that globular cluster surface density distribution can be described by a core model, for which the core radius correlates with galaxy luminosity. Our results favor scenarios in which ellipticals form from massive, gas rich progenitors at early epochs. Detailed simulations of the formation of globular cluster systems would be valuable to draw firmer conclusions.