The magnetic field in the NGC 2024 FIR 5 dense core

TL;DR

This study used SMA observations to map the magnetic field in the NGC 2024 FIR 5 core, revealing a partial hourglass shape, estimating a field strength of 2.2 mG, and analyzing the influence of nearby HII regions and outflows.

Contribution

First high-resolution SMA polarization observations of NGC 2024 FIR 5 revealing magnetic field morphology and strength, and analyzing environmental influences and core substructure.

Findings

Magnetic field shows a partial hourglass morphology.

Field strength estimated at 2.2 mG.

Complex outflow morphology observed in CO maps.

Abstract

We used the Submillimeter Array (SMA) to observe the thermal polarized dust emission from the protostellar source NGC 2024 FIR 5. The polarized emission outlines a partial hourglass morphology for the plane-of-sky component of the core magnetic field. Our data are consistent with previous BIMA maps, and the overall magnetic field geometries obtained with both instruments are similar. We resolve the main core into two components, FIR 5A and FIR 5B. A possible explanation for the asymmetrical field lies in depolarization effects due to the lack of internal heating from FIR 5B source, which may be in a prestellar evolutionary state. The field strength was estimated to be 2.2 mG, in agreement with previous BIMA data. We discuss the influence of a nearby H{\sc ii} region over the field lines at scales of $\sim 0.01$ pc. Although the hot component is probably compressing the molecular gas where the dust core is embedded, it is unlikely that the radiation pressure exceeds the magnetic tension. Finally, a complex outflow morphology is observed in CO (3 $\rightarrow$ 2) maps. Unlike previous maps, several features associated with dust condensations other than FIR 5 are detected.