Stellar velocity dispersion and anisotropy of the Milky Way inner halo

Journal Article · Tue Nov 10 04:00:00 EST 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/813/2/89· OSTI ID:22882441

III, Charles King; Brown, Warren R.; Geller, Margaret J.

We measure the three components of velocity dispersion, σ{sub R}, σ{sub θ}, σ{sub ϕ}, for stars within 6 < R < 30 kpc of the Milky Way using a new radial velocity sample from the MMT telescope. We combine our measurements with previously published data so that we can more finely sample the stellar halo. We use a maximum likelihood statistical method for estimating mean velocities, dispersions, and covariances assuming only that velocities are normally distributed. The alignment of the velocity ellipsoid is consistent with a spherically symmetric gravitational potential. From the spherical Jeans equation, the mass of the Milky Way is M(R⩽12 kpc)=1.3×10{sup 11} M{sub ⊙} with an uncertainty of 40%. We also find a region of discontinuity, 15 ≲ R ≲ 25 kpc, where the estimated velocity dispersions and anisotropies diverge from their anticipated values, confirming the break observed by others. We argue that this break in anisotropy is physically explained by coherent stellar velocity structure in the halo, such as the Sgr stream. To significantly improve our understanding of halo kinematics will require combining radial velocities with future Gaia proper motions.

• OSTI ID: 22882441
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 813; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United Kingdom
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ANISOTROPY
DISPERSIONS
GALACTIC EVOLUTION
MASS
MILKY WAY
PROPER MOTION
RADIAL VELOCITY
SPHERICAL CONFIGURATION
STARS
SYMMETRY
TELESCOPES