Globular Cluster Systems in Other Galaxies

Abstract

Baade and Shapley would surely be surpised and delighted to see how far we have moved from the original view, half a century ago, of globular clusters as the paradigmatic Population II objects. Considerable evidence, accumulated especially over the last decade, now demonstrates that globular cluster systems (GCS’s) make up a stellar population with distinctive characteristics of their own and are not just subsets of the old Pop II field stars that fill the halos of large galaxies. For example, the halo clusters have mean metallicities and metallicity distributions that are often unlike the field halo stars in the same region of their parent galaxy; the spatial structure of the GCS is often quite a bit shallower than the more centrally-concentrated halo and spheroid population; and in some galaxies at least, the GCS is a dynamically and kinematically distinct entity within the halo.