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

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 esti...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society. Letters 2012-07, Vol.424 (1), p.L44-L48
Main Authors: Deason, A. J., Belokurov, V., Evans, N. W., An, J.
Format: Article
Language:English
Subjects:
dark matter
Galaxy: halo
Galaxy: kinematics and dynamics
stars
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Summary: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).
ISSN:1745-3925
1745-3933
DOI:10.1111/j.1745-3933.2012.01283.x