EPoS Contribution
EPoS Contribution
Magnetic Fields and Star Formation: New Observational Tests and Analyses, and Surprising New Results

Richard Crutcher
University of Illinois, Urbana, IL 61801, USA
There are two extreme-case models of star formation:
(1) magnetic fields are strong enough to support clouds against gravitational collapse, and evolution proceeds by ambipolar diffusion building up mass but not magnetic flux in cloud cores, and
(2) magnetic fields are sufficiently weak that the evolution of the ISM and of molecular clouds is governed by turbulence.

In this talk, I report the results of two very recent studies to test these models and determine observationally which dominates the star formation process. One study is the measurement of the differential mass/flux ratio between cloud envelope and core. Ambipolar diffusion requires that this ratio increase from envelope to core, while turbulent simulations usually show a decrease. The comparison of GBT and Arecibo telescope measurements of the Zeeman effect in OH toward dark cloud cores has given a clear result for this test. Two, the problem with Zeeman measurements in general is that only the line-of-sight component B(los) of the total magnetic vector B(total) can be measured. A Bayesian analysis of a set of 141 H I, OH, and CN Zeeman measurements of the line-of-sight component B(los) has provided clear information about the probability density function (pdf) of the total strength B(total) of the magnetic vector and its scaling with density. This Bayesian study also provides a clear test to distinguish between the two models of star formation. The surprising results of these new observations and analyses will be described and the implication for ambipolar diffusion versus turbulence discussed.