Galactic structure from the spacelab infrared telescope. III - A dynamical model for the Milky Way bulge

Abstract

The Milky Way bulge is modeled as an oblate isotropic rotator with constant M/L ratio. A model with M/L2.2 micron = 1 successfully reproduces a variety of stellar velocity dispersion measurements for R between 2 and 1200 pc. An observed increase in the stellar velocity dispersion inside 2 pc requires either that there be an additional central mass of order 3 x 10 exp 6 solar mass or that the stellar motions become anisotropic there. The model has insufficient mass to reproduce the observed peak in the H I and CO rotation curve of 250 km/s at 300 pc; it is argued that the peak arises from noncircular gas motions and does not reflect the true mass of the bulge.