Decomposing Magnetic Fields in Three Dimensions over the Central Molecular Zone

TL;DR

This paper applies the Velocity Gradient Technique to CO data in the Central Molecular Zone to map and analyze three-dimensional magnetic fields, revealing complex magnetic structures and demonstrating the method's effectiveness.

Contribution

The study introduces a novel application of the VGT combined with line decomposition to map 3D magnetic fields in the CMZ, providing new insights into magnetic configurations.

Findings

Magnetic field maps show different orientations in velocity components.

Line-of-sight magnetic field aligns with Planck dust polarization.

Distinct magnetic structures observed in high-velocity features.

Abstract

Measuring magnetic fields in the interstellar medium and obtaining their distribution along line-of-sight is very challenging with the traditional techniques. The Velocity Gradient Technique (VGT), which utilizes anisotropy of magnetohydrodynamic (MHD) turbulence, provides an attractive solution. Targeting the central molecular zone (CMZ), we test this approach by applying the VGT to $\rm ^{12}CO$ and $\rm ^{13}CO$ (J = 1-0) data cubes. We first used the SCOUSEPY algorithm to decompose the CO line emissions into separate velocity components, and then we constructed pseudo-Stokes parameters via the VGT to map the plane-of-the-sky magnetic fields in three-dimension. We present the decomposed magnetic field maps and investigate their significance. While the line-of-sight integrated magnetic field orientation is shown to be consistent with the polarized dust emission from the Planck survey at 353 GHz, individual velocity components may exhibit different magnetic fields. We present a scheme of magnetic field configuration in the CMZ based on the decomposed magnetic fields. In particular, we observe a nearly vertical magnetic field orientation in the dense clump near the Sgr B2 and a change in the outflow regions around the Sgr A*. Two high-velocity structures associated with an expanding ring in the CMZ show distinct swirling magnetic field structures. These results demonstrate the potential power of the VGT to decompose velocity or density-dependent magnetic structures.