Dense gas kinematics and a narrow filament in the Orion A OMC1 region
  using NH3
  We present combined observations of the NH3 (J,K) = (1,1) and (2,2) inversion
transitions towards OMC1 in Orion A obtained by the Karl G. Jansky Very Large
Array (VLA) and the 100 m Robert C. Byrd Green Bank Telescope (GBT). With an
angular resolution of 6" (0.01 pc), these observations reveal with
unprecedented detail the complex filamentary structure extending north of the
active Orion BN/KL region in a field covering 6' x 7'. We find a 0.012 pc wide
filament within OMC1, with an aspect ratio of ~37:1, that was missed in
previous studies. Its orientation is directly compared to the relative
orientation of the magnetic field from the James Clerk Maxwell Telescope BISTRO
survey in Orion A. We find a small deviation of ~11 deg between the mean
orientation of the filament and the magnetic field, suggesting that they are
almost parallel to one another. The filament's column density is estimated to
be 2-3 orders of magnitude larger than the filaments studied with Herschel and
is possibly self-gravitating given the low values of turbulence found. We
further produce maps of the gas kinematics by forward modeling the hyperfine
structure of the NH3 (J,K) = (1,1) and (2,2) lines. The resulting distribution
of velocity dispersions peaks at ~0.5 km/s, close to the subsonic regime of the
gas. This value is about 0.2 km/s smaller than previously measured in
single-dish observations of the same region, suggesting that higher angular and
spectral resolution observations will identify even lower velocity dispersions
that might reach the subsonic turbulence regime in dense gas filaments.
