Submillimetre observations of the two-component magnetic field in M82

Abstract

We observed the starburst galaxy M82 in 850$\mu$m polarised light with the POL-2 polarimeter on the James Clerk Maxwell Telescope (JCMT). We interpret our observed polarisation geometry as tracing a two-component magnetic field: a poloidal component aligned with the galactic 'superwind', extending to a height $\sim 350$ 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 polarised light distribution at galactocentric radii $\gtrsim 2$ kpc. Comparison of our results with recent HAWC+ measurements of the field in the dust entrained by the M82 superwind suggests that the superwind breaks out from the central starburst at $\sim 350$ pc above the plane of the galaxy.

5 pages, 5 figures, accepted by Monthly Notices of the Royal Astronomical Society (MNRAS)

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• Extragalactic magnetism with SOFIA (SALSA Legacy Program) -- IV: Program overview and first results on the polarization fraction
• The JCMT Nearby Galaxies Legacy Survey: SCUBA-2 observations of nearby galaxies
• The magnetic fields of the dusty nuclei and molecular outflows of Arp 220
• Exploring the Magnetic Field Geometry in NGC 891 with SOFIA/HAWC+