Filament intersections and cold dense cores in Orion A North

Abstract

We studied the filament structures and cold dense cores in OMC-2,3 region in Orion A North molecular cloud using the high-resolution N2H+ (1-0) spectral cube observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). The filament network over a total length of 2 pc is found to contain 170 intersections and 128 candidate dense cores. The dense cores are all displaced from the infrared point sources (possible young stars), and the major fraction of cores (103) are located around the intersections. Towards the intersections, there is also an increasing trend for the total column density N-tot as well as the power-law index of the column-density Probability Distribution Function (N-PDF), suggesting that the intersections would in general have more significant gas assembly than the other part of the filament paths. The virial analysis shows that the dense cores mostly have virial mass ratio of alpha(vir) = M-vir/M-gas < 1.0, suggesting them to be bounded by the self-gravity. In the mean time, only about 23 per cent of the cores have critical mass ratio of alpha(cri)t = M-crit/M-gas < 1.0, suggesting them to be unstable against core collapse. Combining these results, it shows that the major fraction of the cold starless and possible pre-stellar cores in OMC-2,3 are being assembled around the intersections, and currently in a gravitationally bound state. But more extensive core-collapse and star formation may still require continuous core mass growth or other perturbations.