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 nonparametric 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) x 10(12) M circle dot, and the exponent of the density profile rho proportional to r(-alpha) in the range 10 - 100 kpc is alpha = 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 r(c) in the range 10 - 500 kpc.