Broken degeneracies: the rotation curve and velocity anisotropy of the
  Milky Way halo
  We use distant Blue Horizontal Branch stars with Galactocentric distances 16
< r/kpc < 48 as kinematic tracers of the Milky Way dark halo. We model the
tracer density as an oblate, power-law embedded within a spherical power-law
potential. Using a distribution function method, we estimate the overall
power-law potential and the velocity anisotropy of the halo tracers. We measure
the slope of the potential to be gamma ~ 0.4 and the overall mass within 50 kpc
is ~ 4 x 10^11 M_sol. The tracer velocity anisotropy is radially biased with
beta ~ 0.5, which is in good agreement with local solar neighbourhood studies.
Our results provide an accurate outer circular velocity profile for the Milky
Way and suggest a relatively high concentration dark matter halo (c_vir ~ 20).
