Mapping the magnetic field in the Taurus/B211 filamentary cloud with SOFIA HAWC+ and comparing with simulation

TL;DR

This study maps the magnetic field in the Taurus B211 filament using SOFIA HAWC+ and compares observations with simulations, revealing complex magnetic structures and varying field strengths across sub-regions.

Contribution

It provides detailed magnetic field measurements in B211, compares observational data with simulations, and discusses the impact of filament substructures on magnetic field perturbations.

Findings

Two sub-regions with different magnetic field strengths identified.

Magnetically critical and sub-Alfvénic in quieter regions.

Super-Alfvénic, multi-velocity component regions show weaker fields.

Abstract

Optical and infrared polarization mapping and recent Planck observations of the filamentary cloud L1495 in Taurus show that the large-scale magnetic field is approximately perpendicular to the long axis of the cloud. We use the HAWC+ polarimeter on SOFIA to probe the complex magnetic field in the B211 part of the cloud. Our results reveal a dispersion of polarization angles of $36^\circ$, about five times that measured on a larger scale by Planck. Applying the Davis-Chandrasekhar-Fermi (DCF) method with velocity information obtained from IRAM 30m C$^{18}$O(1-0) observations, we find two distinct sub-regions with magnetic field strengths differing by more than a factor 3. The quieter sub-region is magnetically critical and sub-Alfv\'enic; the field is comparable to the average field measured in molecular clumps based on Zeeman observations. The more chaotic, super-Alfv\'enic sub-region shows at least three velocity components, indicating interaction among multiple substructures. Its field is much less than the average Zeeman field in molecular clumps, suggesting that the DCF value of the field there may be an underestimate. Numerical simulation of filamentary cloud formation shows that filamentary substructures can strongly perturb the magnetic field. DCF and true field values in the simulation are compared. Pre-stellar cores are observed in B211 and are seen in our simulation. The appendices give a derivation of the standard DCF method that allows for a dispersion in polarization angles that is not small, present an alternate derivation of the structure function version of the DCF method, and treat fragmentation of filaments.