Measuring mass-loss rates from Galactic satellites

We present the results of a study that uses numerical simulations to interpret observations of tidally disturbed satellites around the Milky Way. When analysing the simulations from the viewpoint of an observer, we find a break in the slope of the star count and velocity dispersion profiles in our models at the location where unbound stars dominate. We conclude that 'extratidal' stars and enhanced velocity dispersions observed in the outskirts of Galactic satellites are caused by contamination by stellar debris from the tidal interaction with the Milky Way. However, a significant bound population can exist beyond the break radius and we argue that it should not be identified with the tidal radius of the satellite. We also develop and test a method for determining the mass-loss rate from a Galactic satellite using its extra-tidal population. We apply this method to observations of globular clusters and dwarf spheroidal satellites of the Milky Way, and conclude that a significant fraction of each of these satellite systems is likely to be destroyed within the next Hubble time. Finally, we demonstrate that this mass-loss estimate allows us to place some limits on the initial mass function (IMF) of stars in a cluster from the radial dependence of its present-day mass function (PDMF).