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

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) - 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. Our analysis reveals a complex magnetic-field structure shaped by the combined influence of turbulence and gravity, as evidenced by the distributions of both the alignment measure (AM) and the relative orientation angle (θ r), between the magnetic fields inferred from the VGT and dust polarization observations. The θ r distributions are clearly double-peaked for DCN and HN13C, whereas C18O and H13CO+ predominantly exhibit a preferred perpendicular orientation. 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, for the first time, the application of VGT to a massive protocluster, G327.29, using high-resolution ALMA observations.