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Velocity Shear of the Thick Disk from SPM3 Proper Motions at the South Galactic Pole

T. M. Girard·V. I. Korchagin·D. I. Casetti-Dinescu·W. F. van Altena·C. E. Lopez·D. G. Monet
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Abstract

The kinematical properties of the Galactic Thick Disk are studied using absolute proper motions from the SPM3 Catalog and 2MASS near-infrared photometry for a sample of ~1200 red giants in the direction of the South Galactic Pole. The photometrically-selected sample is dominated by Thick Disk stars, as indicated by the number-density distribution that varies with distance from the Galactic plane as a single-valued exponential over the range 1<z<4 kpc. The inferred scale height of the Thick Disk is 0.783 +/- 0.048 kpc. The kinematics of the sample are also consistent with disk-like motion. The U-velocity component is roughly constant, reflecting the Sun's peculiar motion, while a considerable shear is seen in the mean rotational velocity, V. The V-velocity profile's dependence on z is linear, with a gradient of dV/dz = -30 +/- 3 km/s/kpc. The velocity dispersions, in both U and V, show a lesser gradient of about 9 +/- 3 km/s/kpc. We demonstrate that the derived velocity and velocity-dispersion profiles are consistent with the assumptions of dynamical equilibrium and reasonable models of the overall Galactic potential.

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T. M. Girard, V. I. Korchagin, D. I. Casetti-Dinescu, W. F. van Altena, C. E. Lopez, D. G. Monet. 2006-07-18. Velocity Shear of the Thick Disk from SPM3 Proper Motions at the South Galactic Pole. https://doi.org/10.1086/507331

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