Deriving the mass distribution of M87 from globular clusters

We describe a maximum-likelihood method for determining the mass distribution in spherical stellar systems from the radial velocities of a population of discrete test particles. The method assumes a parametric form for the mass distribution and a non-parametric two-integral distribution function. We apply the method to a sample of 161 globular clusters in M87. We find that the mass within 32 kpc is (2.4 ± 0.6) × 10M⊙, and the exponent of the density profile ρ ∝ r in the range 10 − 100 kpc is α = 1.6 ± 0.4. The energy distribution suggests a few kinematically distinct groups of globular clusters. The anisotropy of the globular-cluster velocity distribution cannot be determined reliably with the present data. Models fitted to an NFW potential yield similar mass estimates but cannot constrain the concentration radius rc in the range 10− 500 kpc. Subject headings: Methods: statistical – galaxies: kinematics and dynamics – galaxies: fundamental parameters – galaxies: individual (M87) – galaxies: star clusters – cosmology: dark matter