2011MNRAS.411.2067L

Recent observational evidence that magnetic fields are dynamically important in molecular clouds, compared to self-gravity and turbulence, is reviewed and illustrated with data from the NGC 2024 region. One piece of evidence, turbulence anisotropy, was found in the diffuse envelope of a cloud (A_v≈ 1; [Heyer et al. 2008]; our data further suggest turbulence anisotropy in the cloud (A_v> 7) and even near the cloud core (A_v∼ 100). The data also show that magnetic fields can channel gravitational contraction even for a region with supercritical N(H₂)/2B_los ratio (the ratio between the observed column density and two times the line-of-sight observed field strength), a parameter which has been widely used by observers to estimate core mass-to-flux ratios. Although the mass-to-flux ratio is constant under the flux-freezing condition, we show that N(H₂)/2B_los grows with time if gravitational contraction is anisotropic due to magnetic fields. The ionized gas at the centre of IC 10: a possible localized chemical pollution by Wolf-Rayet stars