Huddled Masses Yearning to Stream Free: Globular Clusters in the Hearts of Galaxy Clusters

Abstract

Extremely rich populations of globular clusters, numbering ten thousand or more, surround the central giant galaxies in rich clusters. I discuss some recent spectroscopic and photometric observations of these rich globular clusters populations. In very nearby galaxy clusters, the globular cluster velocities can be used to trace the transition from the galaxy potential to the larger cluster potential. Beyond cz \approx 3000 km/s, the globulars are too faint for spectroscopic studies with even the largest telescopes and cease to be useful dynamical tracers. However, the spatial distribution and size of the globular population also contains information on the central mass distribution of the cluster and can be measured out to cz > 20,000 km/s. Overall, the data suggest that these rich globular cluster populations are comprised of normal, old globulars, the majority of which were assembled in the cluster centers before most of the stars in the cD galaxy were formed.