The Globular Clusters of Dwarf Spheroidal Galaxies

Abstract

The possibility that the Sagittarius dwarf spheroidal might have formed as a Searle-Zinn fragment in the outer halo of the Galaxy is discussed. Arguments in favor of this hypothesis are (1) the luminosity distribution of globular clusters in both Sagittarius and in the outer halo (Rgc${r gc}$ -->$t SUBgt {r gc}t/SUBgt $ --> > 80 kpc) appear to be bimodal with peaks near M -->v ~-5 and -10, and (2) the globular clusters in both Sgr and the outer halo have a significantly larger age spread than do the globulars in the inner halo of the Galaxy. However, a counterargument is that only one of the four globulars associated with Sgr has the large half-light diameter that is diagnostic of outer halo clusters. The absence of globular clusters from all Local Group dwarf spheroidal galaxies fainter than M -->v=-12 shows that their specific globular cluster frequency must be lower than it is in the Fornax dwarf spheroidal. This result suggests that Fornax may have had an unusual evolutionary history.