Constraints on the Global Mass-to-Light Ratios and on the Extent of Dark Matter Halos in Globular Clusters and Dwarf Spheroidals

Abstract

The detection of stars in the process of being tidally removed from globular clusters and dwarf spheroidals in the Galaxy's halo provides a strong constraint on their mass-to-light ratios and on the extent of their possible dark matter halos. If a significant dark matter component existed either within or beyond the observed stellar distribution, then stars would not be removed. This is a result of an increase in the tidal radius and mass segregation between luminous stars and the dark matter component. We use numerical simulations to study mass loss from two-component star clusters orbiting within a deeper potential. We find a global upper limit on the mass-to-light ratios of globular clusters, M/L ≲ 2.5, and rule out the possibility that they have extended halos of low-luminosity material. Similarly, the tidal tails of dwarf spheroidals indicate that their dark matter halos must be truncated at ~400 pc; therefore, they have total mass-to-light ratios ≲100.