Radial velocities for outlying satellites and their implications for the mass of the Galaxy

The mass determination of the Galaxy is extended out to large distances by analyzing the radial velocities of the most distant satellites of the Galaxy. Spectroscopic observations of stars in several outlying globular clusters and dwarf spheroidal galaxies are reported, the radial-velocity determinations are discussed, and the kinematics of the system of globular clusters is examined. The results are used to estimate the mass distribution in the Galaxy out to a distance of about 61 kpc for three values of the local circular velocity. It is found that the mass of the Galaxy continues to increase by a factor of 2 to 4 beyond a galactocentric distance of 10 kpc for any reasonable hypothesis regarding the shape of the velocity ellipsoid and that the data are consistent with the massive halo hypothesis of Ostriker et al. (1974) only if the distribution of peculiar velocities is isotropic.