2019ApJ...871...98Z

We compared the magnetic field directions inferred from polarimetry data obtained from 100 pc scale inter-cloud media (ICM) and from subparsec scale molecular cloud cores. The highly correlated result led us to conclude that cloud turbulence must be sub-Alfvenic. Here we extend the study with 0.01 pc cores observed by interferometers. The inferred field directions at this scale significantly deviate from that of the surrounding ICM. An obvious question to ask is whether this high-resolution result contradicts the sub-Alfvenic picture concluded earlier. We performed MHD simulations of a slightly super-critical (magnetic criticality = 2) clouds with Alfvenic Mach number M_A = 0.63 (M_A ≡ <σ_V/V_A>, where σ_V and V_A are, respectively, local 3D velocity dispersion and Alfven velocity; <...>means the average within the entire simulated volume; e.g., Burkhart et al. 2009), which can reproduce the Paper I results, and observed the development toward smaller scales. Interestingly, all subregions hosting cores with n_H2 > 10⁵/cc (the typical density observed by interferometers) possess M_A = 2-3. Not too surprisingly, these slightly super-Alfvenic cores result in B-field orientation offsets comparable to the interferometer observations. The result suggests that gravity can concentrate (and maybe also contribute to, which requires further study to confirm) turbulent energy and create slightly super-Alfvenic cores out of sub-Alfvenic clouds. The results of our simulations also agree with the observed velocity-scale, mass-scale, and field-density relations.