Submillimeter Polarimetric Observations of the Galactic Center

Abstract

We report the first detection of polarized submillimeter emission from the Sagittarius A region at the Galactic center. We observed three separate 2' × 2' fields: one centered on the circumnuclear disk, one centered on the peak of the molecular cloud M-0.02-0.07 (also called the "50 km s-1 cloud"), and one centered on the peak of the molecular cloud M-0.13-0.08 (also called the "20 km s-1 cloud"). Linear polarization at λ = 350 μm was detected in each of the three regions, at a total of 106 distinct sky positions. In the circumnuclear disk, the projected magnetic field directions that we infer from our measurements are similar to those inferred from previous far-infrared (λ = 100 μm) polarimetry. In the "curved ridge" region of M-0.02-0.07 that has been compressed by the expansion of Sgr A East, our results show clearly the effects of this compression on the magnetic field. In M-0.13-0.08, we observe what appears to be a stretched magnetic field, as expected for this tidally sheared cloud. It has been suggested that a "finger-like extension" or "streamer" from M-0.13-0.08 is falling into the circumnuclear disk. We tentatively interpret a flaring of magnetic field lines that we see in M-0.13-0.08 as evidence that the entire cloud has a velocity component in the Galactic eastern direction, i.e., toward the circumnuclear disk. Further observations are needed to test this interpretation. We argue that polarimetry of dust emission provides a promising tool for obtaining new information on the complex dynamics of neutral gas in the Galactic center.