Erik Bertram, Christoph Federrath, Robi Banerjee, Ralf S. Klessen
We study the mass-to-flux ratio (M/\Phi) of clumps and cores in simulations
of supersonic, magnetohydrodynamical turbulence for different initial magnetic
field strengths. We investigate whether the (M/\Phi)-ratio of core and
envelope, R = (M/\Phi)_{core}/(M/\Phi)_{envelope} can be used to distinguish
between theories of ambipolar diffusion and turbulence-regulated star
formation. We analyse R for different Lines-of-Sight (LoS) in various sub-cubes
of our simulation box. We find that, 1) the average and median values of |R|
for different times and initial magnetic field strengths are typically greater,
but close to unity, 2) the average and median values of |R| saturate at average
values of |R| ~ 1 for smaller magnetic fields, 3) values of |R| < 1 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 |R| ~< 1
for the weak and strong magnetic field limit 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 |R| ~< 1. Second, in
the strong field limit, field reversals in the envelope also lead to values |R|
~< 1. 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.
View original:
http://arxiv.org/abs/1111.5539
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