射电天文研究室知识库

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 degrees x 0.6 degrees, 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 +/- 0.16 pc) and the average spacing of sub-clumps is 7.18' +/- 1.19' (0.86 +/- 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 degrees 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 while lower temperatures (below 20 K) 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.