Could bow-shaped magnetic morphologies surround filamentary molecular clouds?

The 3D magnetic field structure of Orion-A

¹ Dominion Radio Astrophysical Observatory, Herzberg Astronomy and Astrophysics Research Centre, National Research Council Canada, PO Box 248, Penticton, BC V2A 6J9, Canada
e-mail: mtahani@ucalgary.ca
² Physics & Astronomy, University of Calgary, Calgary, Alberta, Canada
³ Max-Planck-Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁴ Chalmers University of Technology, Department of Space, Earth and Environment, 412 93 Gothenburg, Sweden

Received: 9 July 2019
Accepted: 17 October 2019

Abstract

Context. A new method based on Faraday rotation measurements recently found the line-of-sight component of magnetic fields in Orion-A and showed that their direction changes from the eastern side of this filamentary structure to its western side. Three possible magnetic field morphologies that can explain this reversal across the Orion-A region are toroidal, helical, and bow-shaped morphologies.

Aims. In this paper, we constructed simple models to represent these three morphologies and compared them with the available observational data to find the most probable morphology(ies).

Methods. We compared the observations with the models and used probability values and a Monte Carlo analysis to determine the most likely magnetic field morphology among these three morphologies.

Results. We found that the bow morphology had the highest probability values, and that our Monte-Carlo analysis suggested that the bow morphology was more likely.

Conclusions. We suggest that the bow morphology is the most likely and the most natural of the three morphologies that could explain a magnetic field reversal across the Orion-A filamentary structure (i.e., bow, helical and toroidal morphologies).