JCMT POL-2 and ALMA Polarimetric Observations of 6000–100 au Scales in the Protostar B335: Linking Magnetic Field and Gas Kinematics in Observations and MHD Simulations

Abstract

Abstract We present our analysis of the magnetic field structures from 6000 to 100 au scales in the Class 0 protostar B335 inferred from our James Clerk Maxwell telescope (JCMT) POL-2 observations and ALMA archival polarimetric data. To interpret the observational results, we perform a series of (non)ideal MHD simulations of the collapse of a rotating nonturbulent dense core, whose initial conditions are adopted to be the same as observed in B335, and generate synthetic polarization maps. The comparison of our JCMT and simulation results suggests that the magnetic field on a 6000 au scale in B335 is pinched and well aligned with the bipolar outflow along the east–west direction. Among all our simulations, the ALMA polarimetric results are best explained with weak magnetic field models having an initial mass-to-flux ratio of 9.6. However, we find that with a weak magnetic field, the rotational velocity on a 100 au scale and the disk size in our simulations are larger than the observational estimates by a factor of several. An independent comparison of our simulations and the gas kinematics in B335 observed with the SMA and ALMA favors strong magnetic field models with an initial mass-to-flux ratio smaller than 4.8. We discuss two possibilities resulting in the different magnetic field strengths inferred from the polarimetric and molecular-line observations: (1) overestimated rotational-to-gravitational energy in B335, and (2) additional contributions in the polarized intensity due to scattering on a 100 au scale.