Extended ammonia observations towards the 'Integral-Shaped Filament'
  Recent observations suggest a scenario in which filamentary structures in the
ISM represent the first step towards clumps/cores and eventually star
formation. The densest filaments would then fragment into prestellar cores
owing to gravitational instability. We seek to understand the roles filamentary
structures play in high-mass star formation. We mapped the integral-shaped
filament (ISF) in NH3 (1, 1) and (2, 2). The whole filamentary structure is
uniformly and fully sampled. We find that the morphology revealed by the map of
velocity-integrated intensity of the NH3 (1, 1) line is closely associated with
the dust ridge. We identify 6 "clumps" related to the well known OMC-1 to 5 and
11 "sub-clumps" within the map and they are separated not randomly but in
roughly equal intervals along the ISF. The average spacing of clumps is
11.30'$\pm$1.31' (1.36$\pm$0.16 pc ) and the average spacing of sub-clumps is
7.18'$\pm$1.19' (0.86$\pm$0.14 pc). These spacings agree well with the
predicted values of the thermal (0.86 pc) and turbulent sausage instability
(1.43 pc) by adopting a cylindric geometry of the ISF with an inclination of
$60^{\circ}$ with respect to the line of sight. We also find a velocity
gradient of about 0.6 km s-1 pc-1 that runs along the ISF which likely arises
from an overall rotation of the Orion A molecular cloud. The inferred ratio
between rotational and gravitational energy is well below unity. Furthermore,
fluctuations are seen in the centroid velocity diagram along the ISF. The OMC-1
to 5 clouds are located close to the local extrema of the fluctuations, which
suggests that there exist gas flows associated with these clumps in the ISF.
The derived NH3 (1, 1) and (2, 2) rotation temperatures in the OMC-1 are about
30-40 K. In OMC-2, OMC-3, and the northern part of OMC-4, we find higher and
lower temperatures at the boundaries and in the interior, respectively.
