Tracing magnetic field morphology using the Velocity Gradient Technique in the presence of CO self-absorption

TL;DR

This paper evaluates the Velocity Gradient Technique (VGT) for mapping magnetic field orientations in molecular clouds using CO isotopologue data, demonstrating its effectiveness in both diffuse and self-gravitating regions.

Contribution

It tests and confirms the applicability of VGT with various CO tracers in different molecular cloud environments, including self-gravitating regions.

Findings

VGT successfully traces magnetic field directions in synthetic CO maps.

The method works in both diffuse and self-gravitating molecular clouds.

VGT provides an alternative to polarimetry for magnetic field studies.

Abstract

Probing magnetic fields in self-gravitating molecular clouds are generally difficult even with the use of the polarimetry. Based on the properties of magneto-hydrodynamic (MHD) turbulence and turbulent reconnection, Velocity Gradient Technique (VGT) provides a new way in tracing magnetic field orientation and strength based on the spectroscopic data. Our study tests the applicability of VGT in various molecular tracers, e.g. 12CO, 13CO, and C18O. By inspecting synthetic molecular line maps of CO isotopologue generated through radiative transfer calculations, we show that the VGT method can be successfully applied in probing the magnetic field direction in the diffuse interstellar medium as well as in self-gravitating molecular clouds.