AAS Meeting #193 - Austin, Texas, January 1999
Session 89. Protoplanetary Disks, Molecular Clouds
Oral, Friday, January 8, 1999, 2:00-3:30pm, Room 6 (A and B)

## [89.01] Magnetic Fields in Molecular Clouds - Observations Confront Theory

R.M. Crutcher (U.IL.)

This paper presents a summary of all 27 available sensitive Zeeman measurements of magnetic field strengths in molecular clouds together with other relevant physical parameters. >From these data input parameters to magnetic star formation theory are calculated and predictions of theory are compared with observations. Results for this cloud sample are: (1) Motions are supersonic but approximately equal to the Alfvén velocity, which suggests that supersonic motions are likely Alfvén waves; (2) The ratio of thermal to magnetic energy \beta < 1, implying that magnetic fields are important in the energetics of molecular clouds; (3) Kinetic and magnetic virial energies are roughly equally important in balancing gravity; (4) Static magnetic fields appear to be insufficient by about a factor of two in supporting clouds against gravity, and there is no direct observational evidence for subcritical clouds; and (5) Magnetic field strengths scale with gas densities as a power law with an exponent of approximately 1/2; this agrees with the prediction of ambipolar diffusion driven star formation, but this scaling may also be predicted simply by Alfvénic motions.