Submillimetre observations of the two-component magnetic field in M82

We observed the starburst galaxy M82 in 850 mu m polarized light with the POL-2 polarimeter on the James Clerk Maxwell Telescope (JCMT). We interpret our observed polarization geometry as tracing a two-component magnetic field: a poloidal component aligned with the galactic 'superwind', extending to a height similar to 350 pc above and below the central bar; and a spiral-arm-aligned, or possibly toroidal, component in the plane of the galaxy, which dominates the 850 mu m polarized light distribution at galactocentric radii greater than or similar to 2 kpc. Comparison of our results with recent High-resolution Airborne Wideband Camera Plus (HAWC+) measurements of the field in the dust entrained by the M82 superwind suggests that the superwind breaks out from the central starburst at similar to 350 pc above the plane of the galaxy.

Automated summary

Observations of the starburst galaxy M82 in 850 mu m polarized light reveal two components of magnetic fields, one aligned with the galactic 'superwind' and another aligned with spiral arms in the galaxy plane. Comparison with HAWC+ measurements suggests that the superwind emerges from the galactic plane at approximately 350 pc above the center of the galaxy.