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

• Published in: Monthly notices of the Royal Astronomical Society. Letters Vol. 424; no. 1; pp. L44 - L48
• Main Authors: Deason, A. J., Belokurov, V., Evans, N. W., An, J.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.07.2012
• Subjects: dark matter; Galaxy: halo; Galaxy: kinematics and dynamics; stars
• ISSN: 1745-3925; 1745-3933
• DOI: 10.1111/j.1745-3933.2012.01283.x

ABSTRACT We use distant blue horizontal branch stars with Galactocentric distances 16 < r < 48 kpc 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 γ∼ 0.4, and the overall mass within 50 kpc is ∼4 × 1011 M⊙. The tracer velocity anisotropy is radially biased with β∼ 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 (cvir∼ 20).