Asymmetric Polarization in Edge-on Spiral Galaxies

Abstract

This thesis presents a study on the asymmetry in the strength of fractional polarization found in edge-on spiral galaxies. This study makes use of observations by the CHANG-ES group, allowing us to study 35 edge-on spiral galaxies observed in multiple arrays in L-band and C-band. By studying the total intensity, polarization, and fractional polarization, a general positive asymmetry was found in both bands for the polarization and fractional polarization. No asymmetry was found in the total intensity, indicating that the asymmetry arises from polarized emission and not an asymmetry of total emission. We found that the asymmetry followed no trend with the mass and star formation rates of the galaxies. To explain the asymmetry, we consider that the magnetic fields in the magnetic spiral arms of the galaxy are ordered along the front of the arm and disordered along the back, as has been observed in galaxies with coincident magnetic and optical spiral arms. An observer would generally see the front of the magnetic spiral arm on the approaching side of the galaxy and the back of the magnetic spiral arm on the receding side. Therefore, they would see an increase of polarization from the ordered magnetic field on the approaching side, while the disordered field on the receding side would have a lower polarization and depolarize emission from the front of the receding side magnetic spiral arm. This would create an asymmetry in the polarization of the galaxy.