Magnetic Field of Molecular Gas Measured with the Velocity Gradient Technique I. Orion A

TL;DR

This study employs the Velocity Gradient Technique to measure magnetic fields in Orion A, demonstrating its effectiveness across different molecular lines and scales, and validating results with dust polarization data.

Contribution

It introduces the application of VGT to Orion A, showing improved accuracy with velocity decomposition and confirming magnetic field measurements with established methods.

Findings

VGT reveals an east-west magnetic field orientation in Orion A.

VGT results agree with Planck dust polarization measurements.

Velocity decomposition enhances VGT accuracy for 12CO lines.

Abstract

Magnetic fields play an important role in the evolution of molecular clouds and star formation. Using the Velocity Gradient Technique (VGT) model, we measured the magnetic field in Orion A using the 12CO, 13CO, and C18O (1-0) emission lines at a scale of 0.07 pc. The measured B-field shows an east-west orientation that is perpendicular to the integral shaped filament of Orion A at large scale. The VGT magnetic fields obtained from 13CO and C18O are in agreement with the B-field that is measured from the Planck 353 GHz dust polarization at a scale of 0.55 pc. Removal of density effects by using a Velocity Decomposition Algorithm can significantly improve the accuracy of the VGT in tracing magnetic fields with the 12CO (1-0) line. The magnetic field strength of seven sub-clouds, OMC-1, OMC-2, OMC-3, OMC-4, OMC-5, L 1641-N, and NGC 1999 has also been estimated with the Davis-Chandrasekhar-Fermi (DCF) and MM2 technique, and these are found to be in agreement with previous results obtained from dust polarization at far-infrared and sub-millimeter wavelengths. At smaller scales, the VGT proves a good method to measure magnetic fields.