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Paper: Transverse Velocity Distribution of the Thick Disk from SPM3 Proper Motions
Volume: 338, Astrometry in the Age of the Next Generation of Large Telescopes
Page: 264
Authors: Girard, T.M.; Korchagin, V.I.; Dinescu, D.I.; van Altena, W.F.; Lopez, C.E.; Monet, D.G.
Abstract: Proper motions from the SPM 3 Catalog have been combined with 2MASS near-infrared photometry for a photometrically selected sample of ~1200 red giants at the South Galactic Pole. The stars are found to be distributed exponentially in the z direction with a scale height of about 780 pc, indicative of the Thick Disk. The U,V velocities are consistent with disk-like motion. The U-component is roughly constant with z, reflecting the peculiar velocity of the Sun. A considerable velocity shear is seen in the mean V-velocity that grows linearly with z. The dispersions in both U and V also show a nearly linear increase as a function of z out to at least 3 kpc.

The shear in the V-component is a consequence of the combined disk/halo gravitational potential and the increase with z in the dynamic pressure that results from the growing velocity dispersion. We find that the measured velocity and velocity-dispersion profiles are inconsistent with a Plummer model and with a simple, spherically symmetric, pseudo-isothermal model of the halo potential.

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