Evolution of Magnetic Fields in High Mass Star Formation: SMA dust polarization image of the UCHII region G5.89-0.39

TL;DR

This study uses high-resolution SMA observations to analyze magnetic field structures in the high-mass star-forming region G5.89-0.39, revealing complex polarization patterns and the influence of stellar feedback on magnetic field morphology.

Contribution

It provides detailed polarization maps at 870 microns and interprets the magnetic field structure and strength in a high-mass star-forming environment, highlighting the impact of stellar feedback.

Findings

Magnetic field strength estimated at 2-3 mG.

Magnetic fields are disturbed by HII region expansion and outflows.

Magnetic energy is dominated by radiation, outflows, and turbulence.

Abstract

We report high angular resolution (3") Submillimeter Array (SMA) observations of the molecular cloud associated with the Ultra-Compact HII region G5.89-0.39. Imaged dust continuum emission at 870 micron reveals significant linear polarization. The position angles (PAs) of the polarization vary enormously but smoothly in a region of 2x10^4 AU. Based on the distribution of the PAs and the associated structures, the polarized emission can be separated roughly into two components. The component "x" is associated with a well defined dust ridge at 870 micron, and is likely tracing a compressed B field. The component "o" is located at the periphery of the dust ridge and is probably from the original B field associated with a pre-existing extended structure. The global B field morphology in G5.89, as inferred from the PAs, is clearly disturbed by the expansion of the HII region and the molecular outflows. Using the Chandrasekhar-Fermi method, we estimate from the smoothness of the field structures that the B field strength in the plane of sky can be no more than 2-3 mG. We then compare the energy densities in the radiation, the B field, and the mechanical motions as deduced from the C^17O 3-2 line emission. We conclude that the B field structures are already overwhelmed and dominated by the radiation, outflows, and turbulence from the newly formed massive stars.