Estimation of the magnetic field strength from ALMA dust polarization in the protocluster G327.29

Abstract

Magnetic fields and turbulence may play crucial roles in the evolution of molecular clouds and ultimately in the formation of dense cores and stars. Despite being studied in many molecular clouds, the exact role of magnetic fields and turbulence in star formation is still poorly understood. We report the high-resolution plane of sky magnetic field (B_pos) morphology towards the high-mass star-forming region G327.29, obtained with the 12-metre configuration of the Atacama Large Millimeter/sub-millimeter Array (ALMA) telescope. From our analysis, we obtain a complex B_pos morphology in which the magnetic field orientation is uniformly distributed across the entire range from -90 to +90 deg. The observed area is composed of one filament and one dense central clump, both of which harbour multiple dense cores. The total magnetic field strengths (Btot) in these regions are 1.7 \pm 0.8 and 3.6 \pm 1.5 mG at a number density (n) of 1.5 \pm 0.3 x 106 and 2.3 \pm 0.7 x 106 cm-3, derived using the Davi-Chandrasekhar-Fermi (DCF) angular dispersion function (ADF) method. The corresponding B_tot obtained using the Skalidi-Tassis (ST) method are 0.6 \pm 0.3 and 1.1 \pm 0.5 mG, approximately three times lower. The virial parameters (α_vir) in these regions are 2.8 \pm 1.9 and 0.5 \pm 0.4, suggesting that the regions may be gravitationally bound or unbound after accounting the errors. The ratio of turbulent to magnetic energy (~0.17-0.34) indicates that the magnetic field is dynamically more important than turbulence. The relative influence of turbulence and magnetic fields on core dynamics appears to depend on how B_tot scales with gas density (\r{ho}) in the densest regions. In summary, this work, enabled by high-resolution ALMA observations, presents a comprehensive analysis of the relative roles of magnetic fields, turbulence, and gravity in regulating high-mass star formation in G327.29.

arXiv commentAccepted for publication in A&A journal (30 August 2026)