A magnetised Galactic halo from inner Galaxy outflows

TL;DR

This paper identifies large-scale magnetised structures in the Milky Way's halo, linking them to star formation-driven outflows and the eROSITA Bubbles, advancing understanding of galactic magnetic fields and evolution.

Contribution

It presents the first identification of kpc-scale magnetised structures in the Milky Way's halo associated with star formation and large-scale outflows, connecting magnetic and thermal halo features.

Findings

Magnetised structures extend far above and below the Galactic plane.

These structures are spatially coincident with the eROSITA Bubbles.

The morphology suggests a common origin from Galactic outflows.

Abstract

Magnetic halos of galaxies are crucial for understanding galaxy evolution, galactic-scale outflows, and feedback from star formation activity. Identifying the magnetised halo of the Milky Way is challenging because of the potential contamination from foreground emission arising in local spiral arms. Additionally, it is unclear how our magnetic halo is influenced by recently revealed large-scale structures such as the X-ray emitting eROSITA Bubbles. Here we report the identification of several kpc-scale magnetised structures based on their polarized radio emission and their gamma-ray counterparts, which can be interpreted as the radiation of relativistic electrons in the Galactic magnetic halo. These non-thermal structures extend far above and below the Galactic plane and are spatially coincident with the thermal X-ray emission from the eROSITA Bubbles. The morphological consistency of these structures suggests a common origin, which can be sustained by Galactic outflows driven by active star-forming regions located in the Galactic Disc at 3-5 kpc from the Galactic Centre. These results reveal how X-ray-emitting and magnetised halos of spiral galaxies can be related to intense star formation activities and suggest that the X-shaped coherent magnetic structures observed in their halos can stem from galaxy outflows.