New light on faint stars – III. Galactic structure towards the South Pole and the Galactic thick disc

Abstract

The technique of photometric parallax is applied to a complete sample of about 12,500 stars brighter than I = 18.0 towards the South Galactic Pole, allowing the stellar luminosity function in absolute visual magnitude, bolometric magnitude, and mass in the solar neighborhood for all absolute magnitudes above the thermonuclear burning limit, to be derived. Also obtained are the density laws with distance from the Galactic plane for each absolute magnitude. The 300 pc scale height component is identified as an old disk, and the 1350 pc scale height component as a Galactic 'thick disk'. The luminosity function and density law of the thick disk are consistent with a substantial flattening of the spheroid isodensity contours by the gravitational potential of the Galactic disk, in agreement with recent observations of several external galaxies.