Filamentary flow and magnetic geometry in evolving cluster-forming molecular cloud clumps
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abstract
We present an analysis of the relationship between the orientation of
magnetic fields and filaments that form in 3D magnetohydrodynamic simulations
of cluster-forming, turbulent molecular cloud clumps. We examine simulated
cloud clumps with size scales of L ~ 2-4 pc and densities of n ~ 400-1000 cm^-3
with Alfven Mach numbers near unity. We simulated two cloud clumps of different
masses, one in virial equilibrium, the other strongly gravitationally bound,
but with the same initial turbulent velocity field and similar mass-to-flux
ratio. We apply various techniques to analyze the filamentary and magnetic
structure of the resulting cloud, including the DisPerSE filament-finding
algorithm in 3D. The largest structure that forms is a 1-2 parsec-long
filament, with smaller connecting sub-filaments. We find that our simulated
clouds, wherein magnetic forces and turbulence are comparable, coherent
orientation of the magnetic field depends on the virial parameter. Subvirial
clumps undergo strong gravitational collapse and magnetic field lines are
dragged with the accretion flow. We see evidence of filament-aligned flow and
accretion flow onto the filament in the subvirial cloud. Magnetic fields
oriented more parallel in the subvirial cloud and more perpendicular in the
denser, marginally bound cloud. Radiative feedback from a 16 Msun star forming
in a cluster in one of our simulations ultimately results in the destruction of
the main filament, the formation of an HII region, and the sweeping up of
magnetic fields within an expanding shell at the edges of the HII region.
