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  • KINEMATICS OF THE STELLAR H...
    KAFLE, Prajwal R; SHARMA, Sanjib; LEWIS, Geraint F; BLAND-HAWTHORN, Joss

    Astrophysical journal/˜The œAstrophysical journal, 12/2012, Volume: 761, Issue: 2
    Journal Article

    Here, we present a kinematic study of the Galactic halo out to a radius of ~60 kpc, using 4664 blue horizontal branch stars selected from the SDSS/SEGUE survey to determine key dynamical properties. Using a maximum likelihood analysis, we determine the velocity dispersion profiles in spherical coordinates (sigma sub(r), sigma sub(theta), sigma sub(phi)) and the anisotropy profile (beta). The radial velocity dispersion profile (sigma sub(r)) is measured out to a galactocentric radius of r ~ 60 kpc, but due to the lack of proper-motion information, sigma sub(theta), sigma sub(phi), and beta could only be derived directly out to r ~ 25 kpc. In the outer parts, in the range 25 < r/kpc < 56, we predict the profile to be roughly constant with a value of beta approximately 0.5. The newly discovered kinematic anomalies are shown not to arise from halo substructures. We also studied the anisotropy profile of simulated stellar halos formed purely by accretion and found that they cannot reproduce the sharp dip seen in the data. From the Jeans equation, we compute the stellar rotation curve (upsilon sub(circ)) of the Galaxy out to r ~ 25 kpc.