Magnetic fields and outflows in the large Bok globule CB 54

TL;DR

This study uses polarimetric observations to analyze magnetic field structures in the Bok globule CB 54, revealing how outflows can influence magnetic fields and providing estimates of magnetic field strength across different scales.

Contribution

It presents new polarimetric data on CB 54, demonstrating the impact of outflows on magnetic field morphology and offering constraints on magnetic field strength in the globule's periphery.

Findings

Magnetic field shows ordered deviation aligned with outflows.

Estimated upper limit of magnetic field strength is <27 μG.

Magnetic field orientation is consistent across multiple scales.

Abstract

We have observed the large Bok globule CB 54 in 850$\mu$m polarised light using the POL-2 polarimeter on the James Clerk Maxwell Telescope (JCMT). We find that the magnetic field in the periphery of the globule shows significant, ordered deviation from the mean field direction in the globule centre. This deviation appears to correspond with the extended but relatively weak $^{12}$CO outflow emanating from the Class 0 sources at the centre of the globule. Energetics analysis suggests that if the outflow is reshaping the magnetic field in the globule's periphery, then we can place an upper limit of $<27\,\mu$G on the magnetic field strength in the globule's periphery. Comparison with archival Planck and CARMA measurements shows that the field in the centre of the globule is consistent over several orders of magnitude in size scale, and oriented parallel to the density structure in the region in projection. We thus hypothesise that while non-thermal motions in the region may be sub-Alfv\'enic, the magnetic field is subdominant to gravity over a wide range of size scales. Our results suggest that even a relatively weak outflow may be able to significantly reshape magnetic fields in star-forming regions on scales $> 0.1$ pc.