The JCMT BISTRO Survey: An 850/450$\mu$m Polarization Study of NGC 2071IR in OrionB

TL;DR

This study uses polarization observations at 450 and 850 micrometers to analyze the magnetic field structure, strength, and dust grain alignment in the star-forming region NGC 2071IR, revealing a pinched magnetic field morphology and its relation to outflows.

Contribution

First simultaneous polarization measurements at 450 and 850 micrometers of NGC 2071IR, providing insights into magnetic field morphology, strength, and dust grain alignment in a star-forming region.

Findings

Magnetic field shows a pinched morphology aligned with bipolar outflows.

Magnetic field strength estimated at 563±421 μG in the core region.

Polarization fractions are higher at 450 μm than at 850 μm, indicating dust grain alignment effects.

Abstract

We present the results of simultaneous 450 $\mu$m and 850 $\mu$m polarization observations toward the massive star forming region NGC 2071IR, a target of the BISTRO (B-fields in Star-Forming Region Observations) Survey, using the POL-2 polarimeter and SCUBA-2 camera mounted on the James Clerk Maxwell Telescope. We find a pinched magnetic field morphology in the central dense core region, which could be due to a rotating toroidal disk-like structure and a bipolar outflow originating from the central young stellar object, IRS 3. Using the modified Davis-Chandrasekhar-Fermi method, we obtain a plane-of-sky magnetic field strength of 563$\pm$421 $\mu$G in the central $\sim$0.12 pc region from 850 $\mu$m polarization data. The corresponding magnetic energy density of 2.04$\times$10$^{-8}$ erg cm$^{-3}$ is comparable to the turbulent and gravitational energy densities in the region. We find that the magnetic field direction is very well aligned with the whole of the IRS 3 bipolar outflow structure. We find that the median value of polarization fractions, 3.0 \%, at 450 $\mu$m in the central 3 arcminute region, which is larger than the median value of 1.2 \% at 850 $\mu$m. The trend could be due to the better alignment of warmer dust in the strong radiation environment. We also find that polarization fractions decrease with intensity at both wavelengths, with slopes, determined by fitting a Rician noise model, of $0.59 \pm 0.03$ at 450 $\mu$m and $0.36 \pm 0.04$ at 850 $\mu$m, respectively. We think that the shallow slope at 850 $\mu$m is due to grain alignment at the center being assisted by strong radiation from the central young stellar objects.