Dynamical Structure of the Galaxy From the Local Kinematics of M Subdwarfs

Computer Science – Databases

Scientific paper

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Scientific paper

A search of the SDSS and SEGUE spectroscopic databases has turned over 10,000 M subdwarfs, most locatd with a few hundred parsecs from the Sun. Kinematics of these low-mass, metal-poor stars were calculated from proper motions, spectroscopic distances, and radial velocity measurements. The distribution reveals that the moderately metal-poor subdwarfs (sdM) have motions consistent with the Galactic thick disk, but with some possibly associated with the Galactic halo. The kinematics of the more metal-poor extreme subdwarfs (esdM) and ultrasubdwarfs (usdM), on the other hand, unambiguously associates them with the halo population. M subdwarfs from both the inner and outer halo are identified, with the outer halo objects displaying significantly lower mean metallicities. While the distribution does not support the existence of local halo substructure (streams), the outer halo subdwarfs show a marked asymmetry in the Galactic rest frame, which suggests that this population may be, on average, counter-rotating with respect to the Galactic disk. This may have interesting implications on models of Galactic formation.

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