Local Surface Density of the Galactic Disk from a Three-Dimensional Stellar Velocity Sample

Abstract

We have reestimated the surface density of the Galactic disk in the solar neighborhood within +/-0.4 kpc of the Sun using the parallaxes and proper motions of a kinematically and spatially unbiased sample of 1476 old bright red giant stars from the Hipparcos catalog with measured radial velocities from Barbier-Brossat & Figon. We determine the vertical distribution of the red giants as well as the vertical velocity dispersion of the sample (14.4+/-0.3 km s^-1) and combine these to derive the surface density of the gravitating matter in the Galactic disk as a function of the Galactic coordinate z. The surface density of the disk increases from 10.5+/-0.5 M_solar pc^-2 within +/-50 pc to 42+/-6 M_solar pc^-2 within +/-350 pc. The estimated volume density of the Galactic disk within +/-50 pc is about 0.1 M_solar pc^-3 which is close to the volume density estimates of the observed baryonic matter in the solar neighborhood.