Magnetic field transport from disk to halo via the galactic chimney process in NGC 6946

TL;DR

This study detects a magnetic field gradient in NGC 6946 linked to star formation, revealing how magnetic fields influence and are influenced by disk-halo interactions and gas dynamics.

Contribution

It provides observational evidence of magnetic field displacement caused by star formation-driven outflows, connecting magnetic field evolution with galactic feedback processes.

Findings

Magnetic field gradient coincides with HI hole and gas infall.

Star formation drives vertical displacement of magnetic fields.

Magnetic fields play a key role in disk-halo interactions.

Abstract

The interstellar medium (ISM) in galaxies is directly affected by the mass and energy outflows originating in regions of star formation. Magnetic fields are an essential ingredient of the ISM, but their connection to the gaseous medium and its evolution remains poorly understood. Here we present the detection of a gradient in Faraday rotation measure (RM), co-located with a hole in the neutral hydrogen (HI) distribution in the disk of the nearby spiral galaxy NGC 6946. The gas kinematics in the same location show evidence for infall of cold gas. The combined characteristics of this feature point to a substantial vertical displacement of the initially plane-parallel ordered magnetic field, driven by a localized star formation event. This reveals how the large-scale magnetic field pattern in galaxy disks is directly influenced by internal energetic phenomena. Conversely, magnetic fields are observed to be an important ingredient in disk-halo interactions, as predicted in MHD simulations. Turbulent magnetic fields at smaller spatial scales than the observed RM gradient will also be carried from the disk and provide a mechanism for the dynamo process to amplify the ordered magnetic field without quenching. We discuss the observational biases, and suggest that this is a common feature of star forming galaxies with active disk-halo flows.