Gas velocity structure of the Orion A Integral Shaped Filament

TL;DR

This study analyzes the gas kinematics of the Orion A Integral Shaped Filament using multiple molecular tracers, revealing velocity gradients, gravitational binding, and complex small-scale structures indicative of dynamic processes.

Contribution

It introduces a novel visualization method for PV structures and provides new insights into the velocity components and small-scale dynamics of the ISF.

Findings

Velocity gradient from north to south with a peak near the ONC

Detection of two CO velocity components suggesting rotation

Identification of small-scale twisting structures with short timescales

Abstract

We present analysis of the gas kinematics of the Integral Shaped Filament (ISF) in Orion~A using four different molecular lines, $^{12}$CO (1-0), $^{13}$CO (1-0), NH$_3$ (1,1), and N$_2$H$^+$ (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 center 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 $^{12}$CO velocity components along the northern half of the ISF; if interpreted as circular rotation, the angular velocity is $\omega=1.4\,{\rm Myr}^{-1}$. On small scales we report the detection of N$_2$H$^+$ and NH$_3$ "twisting and turning" structures, with short associated timescales 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.