DR 21(OH): a highly fragmented, magnetized, turbulent dense core

TL;DR

This study provides high-resolution observations of the DR 21(OH) core, revealing complex magnetic fields, turbulence, and fragmentation, highlighting the interplay of magnetic diffusion, rotation, and gravity in massive star formation.

Contribution

It offers detailed insights into the magnetic field structure, turbulence, and fragmentation processes in a massive star-forming core using high-angular-resolution submillimeter observations.

Findings

Magnetic field shows a toroidal configuration in the core.

Evidence of magnetic field diffusion beyond ambipolar diffusion expectations.

Fragmentation likely driven by rotation and outflow feedback, despite supercritical mass-to-flux ratio.

Abstract

We present high-angular-resolution observations of the massive star forming core DR21(OH) at 880 mum using the Submillimeter Array (SMA). The dense core exhibits an overall velocity gradient in a Keplerian-like pattern, which breaks at the center of the core where SMA 6 and SMA 7 are located. The dust polarization shows a complex magnetic field, compatible with a toroidal configuration. This is in contrast with the large, parsec-scale filament that surrounds the core, where there is a smooth magnetic field. The total magnetic field strengths in the filament and in the core are 0.9 and 2.1 mG, respectively. We found evidence of magnetic field diffusion at the core scales, far beyond the expected value for ambipolar diffusion. It is possible that the diffusion arises from fast magnetic reconnection in the presence of turbulence. The dynamics of the DR 21(OH) core appear to be controlled energetically in equal parts by the magnetic field, magneto-hydrodynamic (MHD) turbulence and the angular momentum. The effect of the angular momentum (this is a fast rotating core) is probably causing the observed toroidal field configuration. Yet, gravitation overwhelms all the forces, making this a clear supercritical core with a mass-to-flux ratio of ~6 times the critical value. However, simulations show that this is not enough for the high level of fragmentation observed at 1000 AU scales. Thus, rotation and outflow feedback is probably the main cause of the observed fragmentation.