SOFIA/HAWC+ traces the magnetic fields in NGC 1068

Abstract

We report the first detection of galactic spiral structure by means of thermal emission from magnetically aligned dust grains. Our 89 $\mu$m polarimetric imaging of NGC 1068 with the High-resolution Airborne Wideband Camera/Polarimeter (HAWC+) on NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA) also sheds light on magnetic field structure in the vicinity of the galaxy's inner-bar and active galactic nucleus (AGN). We find correlations between the 89 $\mu$m magnetic field vectors and other tracers of spiral arms, and a symmetric polarization pattern as a function of the azimuthal angle arising from the projection and inclination of the disk field component in the plane of the sky. The observations can be fit with a logarithmic spiral model with pitch angle of $16.9_{-2.8}^{+2.7}$${}^{\circ }$ and a disk inclination of $48\pm 2^{\circ }$. We infer that the bulk of the interstellar medium from which the polarized dust emission originates is threaded by a magnetic field that closely follows the spiral arms. Inside the central starburst disk ($<1.6$ kpc), the degree of polarization is found to be lower than for far-infrared sources in the Milky Way, and has minima at the locations of most intense star formation near the outer ends of the inner-bar. Inside the starburst ring, the field direction deviates from the model, becoming more radial along the leading edges of the inner-bar. The polarized flux and dust temperature peak $\sim 3-6$" NE of the AGN at the location of a bow shock between the AGN outflow and the surrounding interstellar medium, but the AGN itself is weakly polarized ($<1$%) at both 53 and 89 \um.

13 pages, 7 figures, Accepted for publication by ApJ

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• The Complex Large-scale Magnetic Fields in the First Galactic Quadrant as Revealed by the Faraday Depth Profile Disparity
• A dynamo amplifies the magnetic field of a Milky-Way-like galaxy
• HAWC+ Far-Infrared Observations of the Magnetic Field Geometry in M51 and NGC 891
• Multi-Phase Magnetic Fields in the Galaxy NGC 3627
• The impact of magnetic fields on cosmological galaxy mergers -- II. Modified angular momentum transport and feedback
• On the origin of radio-loudness in active galactic nuclei using far-infrared polarimetric observations
• CosTuuM: polarized thermal dust emission by magnetically oriented spheroidal grains
• Modelling Grain Rotational Disruption by Radiative Torques and Extinction of Active Galactic Nuclei
• Extragalactic magnetism with SOFIA (SALSA Legacy Program) -- IV: Program overview and first results on the polarization fraction
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