The JCMT BISTRO-2 Survey: Magnetic Fields of the Massive DR21 Filament

We present 850 μm dust polarization observations of the massive DR21 filament from the B-fields In STar-formingRegion Observations (BISTRO) survey, using the POL-2 polarimeter and the SCUBA-2 camera on the JamesClerk Maxwell Telescope. We detect ordered magnetic fields perpendicular to the parsec-scale ridge of the DR21main filament. In the subfilaments, the magnetic fields are mainly parallel to the filamentary structures andsmoothly connect to the magnetic fields of the main filament. We compare the POL-2 and Planck dust polarizationobservations to study the magnetic field structures of the DR21 filament on 0.1–10 pc scales. The magnetic fieldsrevealed in the Planck data are well-aligned with those of the POL-2 data, indicating a smooth variation ofmagnetic fields from large to small scales. The plane-of-sky magnetic field strengths derived from angulardispersion functions of dust polarization are 0.6–1.0 mG in the DR21 filament and ∼0.1 mG in the surroundingambient gas. The mass-to-flux ratios are found to be magnetically supercritical in the filament and slightlysubcritical to nearly critical in the ambient gas. The alignment between column density structures and magneticfields changes from random alignment in the low-density ambient gas probed by Planck to mostly perpendicular inthe high-density main filament probed by James Clerk Maxwell Telescope. The magnetic field structures of theDR21 filament are in agreement with MHD simulations of a strongly magnetized medium, suggesting thatmagnetic fields play an important role in shaping the DR21 main filament and subfilaments.