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Session 97 - Galactic Structure, Galactic Center.
Oral session, Friday, January 09
Georgetown,
We present the first submillimeter polarimetric observations of the Sagittarius A region at the Galactic Center. They were obtained at the Caltech Submillimeter Observatory using the University of Chicago polarimeter, Hertz. We detected linear polarization in three regions within Sgr A: the "20 km/s cloud" (M-0.13-0.08), the "50 km/s cloud" (M-0.02-0.07), and the vicinity of the circumnuclear disk.
The polarization mechanism is thermal emission from magnetically aligned interstellar dust grains. Therefore, our observations reveal the orientation of the magnetic field lines within these cold, dense clouds. Our results support the suggestion that the global configuration of the magnetic field within the Galactic Center neutral gas layer is azimuthal with respect to the plane of the Galaxy. This can be contrasted with radio continuum observations that show poloidal fields in ionized regions. The difference can be understood if gravitational forces acting on the dense clouds are stronger than magnetic forces.
For the 50 km/s cloud, the inferred magnetic field direction is parallel to the compression front that lies at the Western edge of this cloud. The compression is due to the interaction with the non-thermal shell source Sgr A East, and the polarization data suggest that the effects of this interaction extend past the compression front, into the center of the cloud.
