The mass distribution in the galactic disc - I. A technique to determine the integral surface mass density of the disc near the Sun

Abstract

A technique for the calculation of the integral surface mass density of the galactic disk at the solar galactocentric distance is discussed. The method employs the observed distribution function of velocities and distances for a sample of tracer stars extending to greater than about 1 kpc from the galactic plane, along with the observed spatial density distribution corresponding to that tracer population. In the second part, this technique has been applied to new photometric and spectroscopic data for a sample of K dwarfs toward the south galactic pole. The results show a total surface mass density of the galactic disk of 46 + or - 9 solar masses/sq pc. In the third part, inconsistencies are pointed out in previous data that suggest that about 50 percent of the local volume mass density is not identified with known stars or with the interstellar medium. Reanalysis of available F dwarf and K giant data using the present models provides no evidence of missing matter in addition to the identified 0.10 solar masses/cu pc.