Broken degeneracies: the rotation curve and velocity anisotropy of the Milky Way halo

Understand

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.