Observation of toroidal magnetic fields on 100 pc scales in the Galactic center

G. Novak,1 D. T. Chuss,1 T. Renbarger,1 G. S. Griffin,2 M. G. Newcomb,2 J. B. Peterson,2
R. F. Loewenstein,3 D. Pernic,3 and J. L. Dotson4

1 Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208
2 Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213
3 Yerkes Observatory, University of Chicago, Williams Bay, WI 53191
4 NASA/Ames Research Center, MS 245-6, Moffett Field, CA 94035

E-mail contact: g-novak@northwestern.edu

astro-ph/0109074

We have recently observed the linear polarization of 450 um continuum emission from the Galactic center using a new polarimetric detector system, called SPARO, that is operated on a 2 m telescope at the South Pole. This new 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 of the Galaxy is permeated by large-scale toroidal magnetic fields. We consider this result together with radio observations that show evidence for poloidal fields and also Faraday rotation observations that probe the line of sight field. It is possible to reconcile these varied observations by invoking a magnetic field geometry similar to that used in the magnetodynamic model of Uchida, Shibata, and Sofue (1985, Nature vol. 317 p. 699). This model was developed in order to explain the Galactic Center Radio Lobe as a magnetically driven gas outflow. We argue that all of the above-mentioned observations of large-scale magnetic fields are fundamentally consistent with the model.