2019MNRAS.489.4771G

We present analysis of the gas kinematics of the integral-shaped filament (ISF) in Orion A using four different molecular lines, ¹²CO (1-0), ¹³CO (1-0), NH₃ (1,1), and N₂H⁺ (1-0). We describe our method to visualize the position-velocity (PV) structure using the intensity-weighted line velocity centroid, which enables us to identify structures that were previously muddled or invisible. We observe a north-to-south velocity gradient in all tracers that terminates in a velocity peak near the centre of the Orion Nebula Cluster (ONC), consistent with the previously reported 'wave-like' properties of the ISF. We extract the velocity dispersion profiles and compare the non-thermal line widths to the gas gravitational potential. We find supersonic Mach number profiles, yet the line widths are consistent with the gas being deeply gravitationally bound. We report the presence of two ¹²CO velocity components along the northern half of the ISF; if interpreted as circular rotation, the angular velocity is ω=1.4 Myr^–1. On small scales we report the detection of N₂H⁺ and NH₃ 'twisting and turning' structures, with short associated time-scales that give the impression of a torsional wave. Neither the nature of these structures nor their relation to the larger scale wave is presently understood.