The Magnetic Field of the H~II Region NGC 6334A

TL;DR

This study measures a very strong magnetic field in the H II region NGC 6334A using Faraday rotation of an extragalactic radio source, revealing insights into magnetic properties of dense star-forming regions.

Contribution

First measurement of a magnetic field as large as 36 microGauss in an H II region using Faraday rotation, highlighting the magnetic flux conservation in dense environments.

Findings

Magnetic field of approximately 36 microGauss in NGC 6334A.

Largest magnetic field measurement for an H II region via this method.

Magnetic to thermal pressure ratio around 5.

Abstract

We have studied the polarization characteristics and Faraday rotation of the extragalactic radio source J17204$-$3554, that appears projected on the north lobe of the galactic H II region NGC 6334A. From observations made with the Very Large Array at 6.0 and 3.6 cm in three different epochs (1994, 1997, and 2006), we estimate a rotation measure of +5100$\pm$900 rad m$^{-2}$ for the extragalactic source. This large rotation measure implies a line-of-sight average magnetic field of $B_\parallel \simeq +36\pm6$ $\mu$G, the largest obtained by this method for an H II region. NGC 6334A is significantly denser than other H II regions studied and this larger magnetic field is expected on the grounds of magnetic flux conservation. The ratio of thermal to magnetic pressure is $\sim$5, in the range of values determined for more diffuse H II regions.