The Magnetic Field Geometry in M82 and Cen A

Abstract

Imaging polarimetry at 1.65 and 2.2 $μ$m is presented for the classic starburst galaxy M82 and the advanced merger system Cen A. Polarimetry at near IR wavelengths allows the magnetic field geometry in galaxies to be probed much deeper into dusty regions than optical polarimetry. In M82, the magnetic field throughout the nucleus has a polar geometry, presumably due to the massive vertical flow that is a result of the intense star formation there. Fully two thirds of the line of sight dust through to the center of M82 contains a vertical magnetic field. In Cen A, the prominent dust lane shows a normal planar field geometry. There is no indication of significant disturbance in the field geometry in the dust lane and the polarization strength is near normal for the amount of extinction. Either the magnetic field geometry was well maintained during the merger, or it reestablished itself very easily.