First Results from Sparo: Evidence for Large-scale Toroidal Magnetic Fields in the Galactic Center

We have observed the linear polarization of 450 μm continuum emission from the Galactic center, using a new polarimetric detector system that is operated on a 2 m telescope at the South Pole. The resulting polarization map extends ∼ 170 pc along the Galactic plane and ∼ 30 pc in Galactic latitude, and thus covers a significant fraction of the central molecular zone. Our map shows that this region is permeated by large-scale toroidal magnetic fields. We consider our results together with radio observations that show evidence for poloidal fields in the Galactic center, and with Faraday rotation observations. We compare all of these observations with the predictions of a magnetodynamic model for the Galactic center that was proposed in order to explain the Galactic Center Radio Lobe as a magnetically driven gas outflow. We conclude that the observations are basically consistent with the model. Subject headings: Galaxy: center — ISM: magnetic fields — polarization