2018A&A...616A.111W

Context. Recent observations suggest a scenario in which filamentary structures in the interstellar medium represent the first step towards clumps/cores and eventually star formation. The densest filaments would then fragment into prestellar cores owing to gravitational instability.
Aims. We seek to understand the roles filamentary structures play in high-mass star formation.
Methods. We mapped the integral-shaped filament (ISF) located at the northern end of the Orion A molecular cloud in NH₃ (1, 1) and (2, 2). The observations were made using the 25 m radio telescope operated by the Xinjiang Astronomical Observatory, Chinese Academy of Sciences. The whole filamentary structure, about 1.2°x0.6°, is uniformly and fully sampled. We investigate the morphology, fragmentation, kinematics, and temperature properties in this region.
Results. 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 revealed by the Herschel Space Observatory. We identify 6 "lumps" related to the well known OMC-1 to 5 and 11 "sub-clumps" within the map. The clumps and sub-clumps are separated not randomly but in roughly equal intervals along the ISF. The average spacing of clumps is 11.30'±1.31' (1.36±0.16pc) and the average spacing of sub-clumps is 7.18'±1.19' (0.86±0.14pc). These spacings agree well with the predicted values of the thermal (0.86pc) and turbulent sausage instability (1.43pc) by adopting a cylindric geometry of the ISF with an inclination of 60° with respect to the line of sight. We also find a velocity gradient of about 0.6km/s/pc 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 30-40K while lower temperatures (below 20K) are obtained in the northern and southern parts of the ISF. 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.