Interaction Between Rogue HI Clouds and the Magnetic Field High Above the Galaxy

TL;DR

This study reveals how high-velocity clouds interact with the Galactic magnetic field at the disk-halo interface, providing new insights into magnetic field structure and the potential for 3D magnetic field mapping.

Contribution

It presents the first observation of magnetic field effects in an HVC and demonstrates a new method for probing Galactic magnetism using polarized radio emission.

Findings

Enhanced magnetic field at the HVC interface.

First imaging of magnetic effects in an HVC.

Potential for 3D Galactic magnetic field reconstruction.

Abstract

Observations of the Milky Way and external galaxies support the idea that large-scale magnetic fields are concentrated in galactic disks, with halo magnetic fields at least an order of magnitude weaker. However, very little is known about the transition between the two. We present the discovery of linearly polarized radio emission at the interface between interacting shells of gas within a well-known grouping of high-velocity clouds (HVCs), the Anti-Center Shell. Faraday rotation of diffuse emission and of background extragalactic compact sources demonstrates an enhancement of the field at the interface. This is the clearest observed example of an HVC altering the large-scale magnetic field at the disk-halo interface and is the first image of magnetic field effects in an HVC. These results demonstrate the possibility of future three-dimensional reconstruction of the Galactic magnetic field and showcase the versatility of the Synthesis Telescope at the Dominion Radio Astrophysical Observatory as one of the few existing telescopes which can exploit this new method of probing Galactic magnetism.