The Average Magnetic Field Strength in Molecular Clouds: New Evidence of Super-Alfvenic Turbulence

Paolo Padoan; Raul Jimenez; Mika Juvela; Aake Nordlund

doi:10.1086/383308

paper

The Average Magnetic Field Strength in Molecular Clouds: New Evidence of Super-Alfvenic Turbulence

arXiv:astro-ph/0311349 · doi:10.1086/383308

Abstract

The magnetic field strength in molecular clouds is a fundamental quantity for theories of star formation. It is estimated by Zeeman splitting measurements in a few dense molecular cores, but its volume--averaged value within large molecular clouds (over several parsecs) is still uncertain. In this work we provide a new method to constrain the average magnetic field strength in molecular clouds. We compare the power spectrum of gas density of molecular clouds with that of two $35 0^{3}$ numerical simulations of supersonic MHD turbulence. The numerical simulation with approximate equipartition of kinetic and magnetic energies (model A) yields the column density power spectrum $P (k) \propto k^{- 2.25 \pm 0.01}$ , the super--Alfvénic simulation (model B) $P (k) \propto k^{- 2.71 \pm 0.01}$ . The column density power spectrum of the Perseus, Taurus and Rosetta molecular cloud complexes is found to be well approximated by a power law, $P_{o} (k) \propto k^{- a}$ , with $a = 2.74 \pm 0.07$ , $2.74 \pm 0.08$ and $2.76 \pm 0.08$ respectively. We conclude that the observations are consistent with the presence of super--Alfvénic turbulence in molecular clouds (model B) while model A is inconsistent (more than 99% confidence) with the observations.

arXiv commentin press ApJL, minor changes to match accepted version

The Average Magnetic Field Strength in Molecular Clouds: New Evidence of Super-Alfvenic Turbulence

Abstract

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