The JCMT BISTRO survey: alignment between outflows and magnetic fields in dense cores/clumps

TL;DR

This study compares outflow directions of low-mass protostars with magnetic field orientations in dense cores, finding a tendency for misalignment that informs models of star formation and magnetic influence.

Contribution

It provides observational evidence of the typical misalignment between outflows and magnetic fields at core scales, supporting models with comparable magnetic and turbulent energies.

Findings

Outflows are generally misaligned with magnetic fields by 15-35 degrees.

Misalignment suggests magnetic fields are twisted at small scales.

Results favor models with balanced magnetic and turbulent energies.

Abstract

We compare the directions of molecular outflows of 62 low-mass Class 0 and I protostars in nearby (<450 pc) star-forming regions with the mean orientations of the magnetic fields on 0.05-0.5 pc scales in the dense cores/clumps where they are embedded. The magnetic field orientations were measured using the JCMT POL-2 data taken by the BISTRO-1 survey and from the archive. The outflow directions were observed with interferometers in the literature. The observed distribution of the angles between the outflows and the magnetic fields peaks between 15 and 35 degrees. After considering projection effects, our results could suggest that the outflows tend to be misaligned with the magnetic fields by 50+/-15 degrees in three-dimensional space and are less likely (but not ruled out) randomly oriented with respect to the magnetic fields. There is no correlation between the misalignment and the bolometric temperatures in our sample. In several sources, the small-scale (1000-3000 au) magnetic fields is more misaligned with the outflows than their large-scale magnetic fields, suggesting that the small-scale magnetic field has been twisted by the dynamics. In comparison with turbulent MHD simulations of core formation, our observational results are more consistent with models in which the energy densities in the magnetic field and the turbulence of the gas are comparable. Our results also suggest that the misalignment alone cannot sufficiently reduce the efficiency of magnetic braking to enable formation of the observed number of large Keplerian disks with sizes larger than 30-50 au.