The Role of Magnetic Fields in the Stability and Fragmentation of Filamentary Clouds: Two Case Studies at OMC-3 and OMC-4

We present the stability analysis of two regions, OMC-3 and OMC-4, in the massive and long molecular cloud complex of Orion A. Using our polarization data obtained by HAWC+/SOFIA at 214 μm and column density and C18O (1-0) archival data, we find that the filamentary cloud and dense clumps in OMC-3 are magnetically supercritical and strongly subvirial. This region should be in the gravitational collapse phase and is consistent with many young stellar objects (YSOs) forming in the region. Our histogram of relative orientations (HROs) analysis shows that magnetic field is dynamically important in the formation of the gas structures in OMC-3. We present the first polarization map of OMC-4. We find that the observed region is generally magnetically subcritical except for an elongated dense core, which could be a result of projection effect of a filamentary structure aligned close to the line-of-sight. Our HROs analysis also points to this possibility. The dominating strong magnetic field in the region is unfavorable for star formation and consistent with much fewer YSOs in the region. We find clear depolarization effect in both observed regions that polarization fractions have anticorrelation with the column density and the dispersion function.