Physical Conditions and Kinematics of the Filamentary Structure in Orion
  Molecular Cloud 1
  We have studied the structure and kinematics of the dense molecular gas in
the Orion Molecular Cloud 1 (OMC1) region with the N2H+ 3-2 line. The 6'x9'
(~0.7x1.1 pc) region surrounding the Orion KL core has been mapped with the
Submillimeter Array (SMA) and the Submillimeter Telescope (SMT). The combined
SMA and SMT image having 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-LTE
analysis using the N2H+ 3-2 and 1-0 data, the density and temperature of the
filaments are estimated to be ~10^7 cm-3 and ~15-20 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 the shielding from the external heating due to
the dense gas in the filaments. The OMC1 region consists of three sub-regions,
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.
