Observations of Magnetic Fields in Molecular Clouds — Testing Star Formation Paradigms

Abstract

Observations of magnetic fields in molecular clouds are essential for understanding their role in the evolution of dense clouds and in the star formation process. I first briefly describe the observational techniques available for such observations — the Zeeman effect, mapping of polarized dust emission, and mapping of linearly polarized line emission. I then describe three predictions of the two extreme paradigms for what drives star formation — magnetic and thermal support with ambipolar diffusion, and compressible turbulence with negligible magnetic fields — that can be tested with observations of magnetic fields. Two exemplar observational results are presented, for the low‐mass star formation region L1544 and for the high‐mass star formation region DR21OH. The data are then used to carry out the tests. The conclusion is that magnetic fields are strong in star formation regions and the magnetic support model is consistent with the data, but both turbulence and strong magnetic fields are important in t...