Multi-Scale Analysis of Magnetic Fields in Filamentary Molecular Clouds in Orion A

TL;DR

This study presents multi-scale polarization measurements in Orion A, revealing complex magnetic field structures, including possible helical components, and demonstrating the spatial connection and rotation of magnetic fields in the region.

Contribution

It provides new multi-scale polarization data and interprets magnetic field configurations, including evidence for a twisted, possibly helical, magnetic field in Orion A.

Findings

Magnetic fields inside Orion A are spatially connected.

Evidence of magnetic field rotation by up to 60 degrees.

Indications of a helical magnetic field component wrapping the filament.

Abstract

New visible and K-band polarization measurements on stars surrounding molecular clouds in Orion A and stars in the BN vicinity are presented. Our results confirm that magnetic fields located inside the Orion A molecular clouds and in their close neighborhood are spatially connected. On and around the BN object, we measured the angular offsets between the K-band polarization data and available submm data. We find high values of the polarization degree, P_{K}, and of the optical depth, \tau_{K}, close to an angular offset position of 90^{\circ} whereas lower values of P_{K} and \tau_{K} are observed for smaller angular offsets. We interpret these results as evidence for the presence of various magnetic field components toward lines of sight in the vicinity of BN. On a larger scale, we measured the distribution of angular offsets between available H-band polarization data and the same submm data set. Here we find an increase of <P_{H}> with angular offset which we interpret as a rotation of the magnetic field by \lesssim 60^{\circ}. This trend generalizes previous results on small scale toward and around lines of sight to BN and is consistent with a twist of the magnetic field on a larger scale towards OMC-1. A comparison of our results with several other studies suggests that a two-component magnetic field, maybe helical, could be wrapping the OMC-1 filament.