Extragalactic Magnetic Fields Mapped in the Far Infrared with HAWC+ on SOFIA

An important legacy from HAWC+ polarimetry on SOFIA is the demonstration that magnetic fields can be detected and analyzed in star-forming galaxies in the far infrared. Fifteen galaxies, and also the 30 Doradus region of the Large Magellanic Cloud, were mapped in polarization within the 53 to 214 micron wavelength range, where the emission traces primarily dense gas heated by young stars, providing unique insights to the magnetic fields in these galaxies. All of the galaxies studied have detectable polarization fraction in the range 1% to 3% or more. The more face-on spiral galaxies in the sample (M51, NGC 1068, and others) show a clear ordered spiral component on scales of several kpc. The edge-on spirals show a mix of planar and, in a minority of cases, outflow field structures, with outflows more visible in the warmer dust emission. The most edge-on galaxy, NGC 891, shows only an isolated instance of outflow magnetic field (perpendicular to the plane) and otherwise a surprisingly low fractional polarization outside the plane, suggesting disordered magnetic fields there. The magnetic field maps of the spirals also trace bar and other nuclear features in the galaxies. In the category of merger systems, the magnetic field in the warped disk of Centaurus A has been studied in detail, and polarization has been mapped in the Antennae galaxy pair including the tidal tail. The successful effort with HAWC+ sets the stage for further breakthroughs in extragalactic magnetic field studies with a cryogenic space telescope.