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

Optical and infrared polarization mapping and recent Planck observations of the filametary 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 degrees, about five times that measured on a larger scale by Planck. Applying the Davis-Chandrasekhar-Fermi (DCF) method with velocity information obtained from Institut de Radioastronomie Millimetrique 30 m (CO)-O-18(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-Alfvenic; the field is comparable to the average field measured in molecular clumps based on Zeeman observations. The more chaotic, super-Alfvenic 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.

Automated summary

Optical and infrared polarization mapping, as well as recent Planck observations, have been used to study the magnetic field properties of the filamentary cloud L1495 in Taurus. The HAWC+ polarimeter on SOFIA was used to investigate the complex magnetic field in the B211 part of the cloud. The results show a significant dispersion of polarization angles and reveal the existence of two distinct sub-regions with different magnetic field strengths.