# Tracing Multi-Scale Magnetic Field Structure Using Multiple Chemical Tracers in Giant Molecular Clouds

## TL;DR

This study demonstrates that the Velocity Gradient Technique, applied to multiple chemical tracers with different optical depths, effectively maps magnetic field structures in molecular clouds, aligning well with polarization observations.

## Contribution

It validates the use of multiple chemical tracers in the Velocity Gradient Technique for detailed magnetic field mapping in giant molecular clouds.

## Key findings

- Good correspondence between velocity gradient and polarization-based magnetic field maps.
- Combining tracers improves magnetic field structure reconstruction.
- Limited signatures of gravitational collapse detected in the cloud.

## Abstract

Probing magnetic fields in Giant Molecular Clouds is often challenging. Fortunately, recently simulations show that analysis of velocity gradients (the Velocity Gradient Technique) can be used to map out the magnetic field morphology of different physical layers within molecular clouds when applied CO isotopologues with different optical depths. Here, we test the effectiveness of the Velocity Gradient Technique in reconstructing the magnetic field structure of the molecular cloud Vela C, employing seven chemical tracers that have different optical depths, i.e. 12CO, 13CO, C18O, CS, HNC, HCO+, and HCN. Our results show good correspondence between the magnetic field morphology inferred from velocity gradients using these different molecular tracers and the magnetic field morphology inferred from BLASTPol polarization observations. We also explore the possibility of using a combination of velocity gradients for multiple chemical tracers to explain the structure of the magnetic field in molecular clouds. We search for signatures of gravitational collapse in the alignment of the velocity gradients and magnetic field and conclude that collapsing regions constitute a small fraction of the cloud.