Physical Conditions and Kinematics of the Filamentary Structure in Orion Molecular Cloud 1

Abstract

We have studied the structure and kinematics of the dense molecular gas in the Orion Molecular Cloud 1 (OMC1) region with the N 2 H + 3–2 line. The 6′ × 9′ (∼0.7 × 1.1 pc) region surrounding the Orion Kleinmann–Low (KL) core has been mapped with the Submillimeter Array (SMA) and the Submillimeter Telescope (SMT). The combined SMA and SMT image, with a resolution of ∼5.″4 (∼2300 au), reveals multiple filaments with a typical width of 0.02–0.03 pc. On the basis of the non-local thermodynamic equilibrium analysis using the N 2 H + 3–2 and 1–0 data, the density and temperature of the filaments are estimated to be ∼10 7 cm −3 and ∼15 K–20 K, respectively. The core fragmentation is observed in three massive filaments, one of which shows the oscillations in the velocity and intensity that could be the signature of core-forming gas motions. The gas kinetic temperature is significantly enhanced in the eastern part of OMC1, likely due to the external heating from the high-mass stars in M42 and M43. In addition, the filaments are colder than their surrounding regions, suggesting shielding from the external heating due to the dense gas in the filaments. The OMC1 region consists of three subregions, i.e., north, west, and south of Orion KL, having different radial velocities with sharp velocity transitions. There is a north-to-south velocity gradient from the western to the southern regions. The observed velocity pattern suggests that dense gas in OMC1 is collapsing globally toward the high-mass star-forming region, Orion Nebula Cluster.