Magnetic field morphological diagnostics with ALMA in the G327.29 protocluster: VGT versus dust polarization

TL;DR

This study compares magnetic field morphology in the G327.29 protocluster using the velocity gradient technique and dust polarization, revealing complex magnetic structures influenced by turbulence and gravity, with the first application of VGT to a massive protocluster.

Contribution

It introduces the application of the velocity gradient technique to a massive protocluster using high-resolution ALMA data, providing new insights into magnetic field structures.

Findings

Magnetic fields are shaped by turbulence and gravity.

Evidence of large-scale gravitational infall onto the filament.

Cores are influenced by a mix of turbulence and gravity.

Abstract

Magnetic fields and turbulence may play a key role in the evolution of protoclusters, influencing the formation of dense cores and stars. Here, we examine the morphology of the magnetic fields in the G327.29 protocluster using both the velocity gradient technique (VGT) extracted from molecular line emissions and linear polarization in the dust continuum emission. The VGT analysis is performed using four molecular tracers: DCN (3-2), C18O (2-1), HN13C (3-2), and H13CO+ (3-2) - which probe gas across different density regimes, observed with the ALMA 12 m array. Owing to its sensitivity to gas dynamics, a comparison between VGT and dust polarization provides a powerful probe of the evolutionary processes in massive star-forming regions. From our analysis we reveal a complex magnetic-field structure, shaped by the combined influence of turbulence and gravity. In addition, it also appears that there is a large-scale (beyond the core scale) gravitational infall from the surrounding medium on to the filament and the central densest region. Furthermore, we observe that cores are dominated by a mix of turbulence and gravity. Overall, this work presents, likely for the first time, the application of VGT to a massive protocluster, G327.29, using high-resolution ALMA observations.