2016MNRAS.459.4130O

We report the detection of a wing component in NH₃ emission towards the starless core TUKH122 with subthermal turbulence in the Orion A cloud. This NH₃ core is suggested to be on the verge of star formation because the turbulence inside the NH₃ core is almost completely dissipated, and also because it is surrounded by CCS, which resembles the prestellar core L1544 in Taurus showing infall motions. Observations were carried out with the Nobeyama 45-m telescope at 0.05 km/s velocity resolution. We find that the NH₃ line profile consists of two components. The quiescent main component has a small linewidth of 0.3 km/s dominated by thermal motion, and the red-shifted wing component has a large linewidth of 1.36 km/s representing turbulent motion. These components show kinetic temperatures of 11 and J=1-0) and CS (J=2-1) lines. Large Velocity Gradient (LVG) model calculations for CS and CO show that the turbulent gas has a temperature of 8-13 K and an H₂ density of ∼10⁴/cm3, suggesting that the temperature of the turbulent component is also ∼10 K. The detections of both NH₃ quiescent and wing components may indicate a sharp transition from the turbulent parent cloud to the quiescent dense core.