Statistical analysis of the mass-to-flux ratio in turbulent cores: effects of magnetic field reversals and dynamo amplification

We study the mass-to-flux ratio M/I of clumps and cores in simulations of supersonic, magnetohydrodynamical turbulence for different initial magnetic field strengths. We investigate whether the M/I of core and envelope, inline image can be used to distinguish between theories of ambipolar diffusion and turbulence-regulated star formation. We analyse inline image for different lines of sight (LoSs) in various subcubes of our simulation box. We find that (1) the average and median values of inline image for different times and initial magnetic field strengths are typically greater than or equal to1; (2) the average and median values of inline image saturate at inline image for smaller magnetic fields; and (3) values of inline image for small magnetic fields in the envelope are caused by field reversals when turbulence twists the field lines such that field components in different directions average out. Finally, we propose two mechanisms for generating values inline image for the weak and strong magnetic field limits in the context of a turbulent model. First, in the weak field limit, the small-scale turbulent dynamo leads to a significantly increased flux in the core and we find inline image. Secondly, in the strong field limit, field reversals in the envelope also lead to values inline image. These reversals are less likely to occur in the core region where the velocity field is more coherent and the internal velocity dispersion is typically subsonic.