The Super-Alfv\'enic Model of Molecular Clouds: Predictions for Mass-to-Flux and Turbulent-to-Magnetic Energy Ratios

TL;DR

This study uses simulations of super-Alfvénic turbulence to predict magnetic and energy ratios in molecular cloud cores, aligning with recent Zeeman effect observations and challenging the necessity of strong large-scale magnetic fields.

Contribution

It demonstrates that super-Alfvénic turbulence models can reproduce observed magnetic and energy ratios without requiring strong large-scale magnetic fields.

Findings

Simulated cores match observed mass-to-flux ratios.

Magnetic field strengths in dense cores align with observations.

Strong large-scale magnetic fields are not necessary to explain Zeeman measurements.

Abstract

Recent measurements of the Zeeman effect in dark-cloud cores provide important tests for theories of cloud dynamics and prestellar core formation. In this Letter we report results of simulated Zeeman measurements, based on radiative transfer calculations through a snapshot of a simulation of supersonic and super-Alfv\'enic turbulence. We have previously shown that the same simulation yields a relative mass-to-flux ratio (core versus envelope) in agreement with the observations (and in contradiction with the ambipolar-drift model of core formation). Here we show that the mass-to-flux and turbulent-to-magnetic-energy ratios in the simulated cores agree with observed values as well. The mean magnetic field strength in the simulation is very low, \bar{B}=0.34 \muG, presumably lower than the mean field in molecular clouds. Nonetheless, high magnetic field values are found in dense cores, in agreement with the observations (the rms field, amplified by the turbulence, is B_{rms}=3.05 \muG). We conclude that a strong large-scale mean magnetic field is not required by Zeeman effect measurements to date, although it is not ruled out by this work.