The Magnetic Field in the Inner 70 Parsecs of the Milky Way

Abstract

Existing radiofrequency data on the center of the Galaxy are used to defend the hypothesis that the magnetic field within a radius of at least 70 pc of the nucleus has a poloidal geometry, is relatively uniform in strength, and is very strong relative to extended fields measured elsewhere in the Galaxy, having a flux density greater than or about a milligauss. The implications of this strong, pervasive field are: 1) that a strong ring current is present at radii beyond 70 pc, and 2) that the dynamics of molecular clouds in the Galactic center are significantly affected by, though probably not dominated by, the magnetic field. At radii within 5 pc, far-IR polarization data suggest a substantial deviation of the magnetic field from a poloidal geometry, at least within the gas and dust layer. There, the coupling of the field to the rapidly orbiting gas near the nucleus is presumably responsible for this local distortion of the larger-scale field geometry.