EPoS Contribution
EPoS Contribution
CARMA Studies of Magnetic Fields in Dense Molecular Clouds

Richard Crutcher
University of Illinois, Urbana, IL, USA
The Zeeman effect in molecular lines is the only available technique for directly measuring magnetic field strengths in molecular clouds. However, there are two limitations in applying Zeeman results to understanding the role of magnetic fields in star formation. First, it is necessary to understand what physical conditions the Zeeman species samples. Second, the Zeeman effect measures only the line-of-sight component of the magnetic field. Without information about the total magnetic field strength, it is necessary to depend on statistical studies. In order to address these two matters, we have carried out CARMA observations at high angular resolution of the molecular clouds W3OH, DR21OH, OMC1, G10.6, S255, and S140, all of which have Zeeman detections in the 113 GHz N=1-0 lines (Falgarone et al., A&A 487, 247, 2008). Lines of C18O, CN, HCN, HCO+, and N2H+ were mapped at typically 2 arcsec resolution. We compared the spatial distributions of the different lines in order to improve understanding of the physical conditions sampled by the Zeeman species CN. We also tested and then applied the Houde et al. (ApJ 536, 857, 2000) technique for inferring the angle between the magnetic field and the line of sight. This technique is based on the fact that for MHD turbulence, motion of ions is constrained by the magnetic field, while the motion of neutrals is not. Hence, for co-located molecular species, the line widths of ions is predicted to be smaller than those of neutrals, with the ratio depending on the angle between the magnetic field and the line of sight. In this presentation I discuss: (1) results for the physical conditions sampled by the CN Zeeman detections, (2) to what extent ion and neutral species are co-located on small spatial scales, and (3) the results of applying the Houde technique to infer TOTAL magnetic field strengths. Implications for molecular cloud evolution and star formation will be discussed.
N. Hakobian, U. Ill., USA