The shape of the Galaxy

The mechanisms responsible for the deviation from circular symmetry in the emission from the outermost atomic H gas of the Galaxy, as seen in the 21-cm survey of the Galactic plane by Weaver and Williams (1974), are investigated theoretically. The analysis of this data set and the construction of a triaxial spheroid model to account for the observations are explained, and it is concluded (1) that the deviations are due to the quadrupole term in the gravitational potential, (2) that the local standard of rest is moving radially outward at velocity 14 km/sec with respect to the most distant H I gas, and (3) that the ellipticity of gas streamlines decreases with increasing distance from the Galactic center, so that (4) the outermost gas is moving in nearly circular orbits. The predictions of the triaxial spheroid model and specific observed features are compared in detail and illustrated with graphs and diagrams. 72 refs