Polarized Light from Massive Protoclusters (POLIMAP). I. Dissecting the role of magnetic fields in the massive infrared dark cloud G28.37+0.07

Magnetic fields may play a crucial role in setting the initial conditions of massive star and star cluster formation. To investigate this, we report SOFIA-HAWC+ 214 μm observations of polarized thermal dust emission and high-resolution GBT-Argus C^18O(1-0) observations toward the massive Infrared Dark Cloud (IRDC) G28.37+0.07. Considering the local dispersion of B-field orientations, we produce a map of B-field strength of the IRDC, which exhibits values between ∼0.03 - 1mG based on a refined Davis-Chandrasekhar-Fermi (r-DCF) method proposed by Skalidis & Tassis. Comparing to a map of inferred density, the IRDC exhibits a B-n relation with a power law index of 0.51±0.02, which is consistent with a scenario of magnetically-regulated anisotropic collapse. Consideration of the mass-to-flux ratio map indicates that magnetic fields are dynamically important in most regions of the IRDC. A virial analysis of a sample of massive, dense cores in the IRDC, including evaluation of magnetic and kinetic internal and surface terms, indicates consistency with virial equilibrium, sub-Alfvénic conditions and a dominant role for B-fields in regulating collapse. A clear alignment of magnetic field morphology with direction of steepest column density gradient is also detected. However, there is no preferred orientation of protostellar outflow directions with the B-field. Overall, these results indicate that magnetic fields play a crucial role in regulating massive star and star cluster formation and so need to be accounted for in theoretical models of these processes.