Structural details of the Sagittarius A complex - Evidence for a large-scale poloidal magnetic field in the Galactic center region

Abstract

Radio observations of the Sgr A complex at both 6 and 20 cm indicate that the diffuse radio structure surrounding Sgr A East and Sgr A West consists of two large-scale components. The first of these is a 20 pc diameter halo which appears to be associated with the nonthermal Sgr A East shell source and which is elongated along the Galactic plane. This source can be described by a model which represents an explosion taking place in a uniform poloidal magnetic field. The second large-scale component is a set of narrow radio streamers running roughly perpendicular to the Galactic plane. They are probably associated with the thermal source Sgr A West, which is coincident with the Galactic nucleus. Hypotheses which might account for the structure of these streamers are discussed. The data show clearly that the bulk of Sgr A West is located in front of Sgr A East.