The Magnetized Disk-Halo Transition Region of M51

TL;DR

This study uses multi-frequency radio polarization observations of M51, including new S-band data, to model the transition of magnetic fields from the galaxy's disk to halo, revealing the complex magneto-ionic structure.

Contribution

It introduces new S-band polarization data for M51 and compares different depolarization models to better understand the disk-halo magnetic transition.

Findings

S-band data are crucial for distinguishing between models.

Magnetic field strengths in disk and halo need adjustment for accurate modeling.

The multilayer magneto-ionic medium model explains the polarization observations.

Abstract

An excellent laboratory for studying large scale magnetic fields is the grand de- sign face-on spiral galaxy M51. Due to wavelength-dependent Faraday depolarization, linearly polarized synchrotron emission at different radio frequencies gives a picture of the galaxy at different depths: Observations at L-band (1-2 GHz) probe the halo region while at C- and X- band (4-8 GHz) the linearly polarized emission probe the disk region of M51. We present new observations of M51 using the Karl G. Jansky Very Large Array (VLA) at S-band (2-4 GHz), where previously no polarization observations existed, to shed new light on the transition region between the disk and the halo. We discuss a model of the depolarization of synchrotron radiation in a multilayer magneto-ionic medium and compare the model predictions to the multi-frequency polarization data of M51 between 1-8GHz. The new S-band data are essential to distinguish between different models. Our study shows that the initial model parameters, i.e. the total reg- ular and turbulent magnetic field strengths in the disk and halo of M51, need to be adjusted to successfully fit the models to the data.