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

TL;DR

This study uses dust polarization observations to analyze magnetic field structures in the DR21 filament, revealing ordered magnetic fields aligned with filamentary structures and their significant role in filament formation.

Contribution

First detailed magnetic field mapping of the DR21 filament across multiple scales, demonstrating the magnetic influence on filament morphology and dynamics.

Findings

Magnetic fields are perpendicular to the main filament and parallel in sub-filaments.

Magnetic field strengths are 0.6--1.0 mG in the filament and ~0.1 mG in ambient gas.

Mass-to-flux ratios indicate a supercritical state in the filament.

Abstract

We present 850 $\mu$m dust polarization observations of the massive DR21 filament from the B-fields In STar-forming Region Observations (BISTRO) survey, using the POL-2 polarimeter and the SCUBA-2 camera on the James Clerk Maxwell Telescope. We detect ordered magnetic fields perpendicular to the parsec-scale ridge of the DR21 main filament. In the sub-filaments, the magnetic fields are mainly parallel to the filamentary structures and smoothly connect to the magnetic fields of the main filament. We compare the POL-2 and Planck dust polarization observations to study the magnetic field structures of the DR21 filament on 0.1--10 pc scales. The magnetic fields revealed in the Planck data are well aligned with those of the POL-2 data, indicating a smooth variation of magnetic fields from large to small scales. The plane-of-sky magnetic field strengths derived from angular dispersion functions of dust polarization are 0.6--1.0 mG in the DR21 filament and $\sim$ 0.1 mG in the surrounding ambient gas. The mass-to-flux ratios are found to be magnetically supercritical in the filament and slightly subcritical to nearly critical in the ambient gas. The alignment between column density structures and magnetic fields changes from random alignment in the low-density ambient gas probed by Planck to mostly perpendicular in the high-density main filament probed by JCMT. The magnetic field structures of the DR21 filament are in agreement with MHD simulations of a strongly magnetized medium, suggesting that magnetic fields play an important role in shaping the DR21 main filament and sub-filaments.