Optical Polarization of M 82

Abstract

We observed a sample of nearby galaxies using the CCD-Polarimeter of the Landessternwarte Heidelberg in the R-Band with the 1.23-m telescope of the MPIA at Calar Alto. In most cases polarization was found but the polarization structures cannot be easily related to a single phenomenon. If there is a strong point source, Rayleigh scattering leads to circular patterns of the polarization vectors. If dust grains are aligned in a magnetic field, this so-called Davis-Greenstein-mechanism gives more uniformly distributed E-vectors, which can be distinguished from the Rayleigh scattering. The example of M 82 given here shows both kinds of polarized light. There is evidence of a strong magnetic field component perpendicular to the disk which seems to have its origin in the center of the galaxy. This is consistent with theoretical models as well as with previous observations.