SOFIA Far Infrared Imaging Polarimetry of M82 and NGC 253: Exploring the Super-Galactic Wind

Abstract

We present Far-Infrared polarimetry observations of M82 at 53 and $154\hat{I}¼\mathrm{m}$ and NGC 253 at $89\hat{I}¼\mathrm{m}$, which were taken with HAWC+ in polarimetry mode on the Stratospheric Observatory for Infrared Astronomy (SOFIA). The polarization of M82 at $53\hat{I}¼\mathrm{m}$ clearly shows a magnetic field geometry perpendicular to the disk in the hot dust emission. For M82 the polarization at $154\hat{I}¼\mathrm{m}$ shows a combination of field geometry perpendicular to the disk in the nuclear region, but closer to parallel to the disk away from the nucleus. The fractional polarization at $53\hat{I}¼\mathrm{m}$ $(154\hat{I}¼\mathrm{m})$ ranges from 7% (3%) off nucleus to 0.5% (0.3%) near the nucleus. A simple interpretation of the observations of M82 invokes a massive polar outflow, dragging the field along, from a region $\sim 700$~pc in diameter that has entrained some of the gas and dust, creating a vertical field geometry seen mostly in the hotter $(53\hat{I}¼\mathrm{m})$ dust emission. This outflow sits within a larger disk with a more typical planar geometry that more strongly contributes to the cooler $(154\hat{I}¼\mathrm{m})$ dust emission. For NGC 253, the polarization at $89\hat{I}¼\mathrm{m}$ is dominated by a planar geometry in the tilted disk, with weak indication of a vertical geometry above and below the plane from the nucleus. The polarization observations of NGC 253 at $53\hat{I}¼\mathrm{m}$ were of insufficient S/N for detailed analysis.

6 Figures, 20 pages, ApJL accepted