Multicomponent Kinematics in a Massive Filamentary Infrared Dark Cloud

To probe the initial conditions for high-mass star and cluster formation, we investigate the properties of dense filaments within the infrared dark cloud (IRDC) G035.39-00.33 (G035.39) in a combined Very Large Array and Green Bank Telescope mosaic tracing the NH₃ (1, 1) and (2, 2) emission down to 0.08 pc scales. Using agglomerative hierarchical clustering on multiple line-of-sight velocity component fitting results, we identify seven extended velocity-coherent components in our data, likely representing spatially coherent physical structures, some exhibiting complex gas motions. The velocity gradient magnitude distribution peaks at its mode of 0.35 and has a long tail extending into higher values of 1.5-2 , and it is generally consistent with those found toward the same cloud in other molecular tracers and with the values found toward nearby low-mass dense cloud cores at the same scales. Contrary to observational and theoretical expectations, we find the nonthermal ammonia line widths to be systematically narrower (by about 20%) than those of N₂H⁺ (1-0) line transition observed with similar resolution. If the observed ordered velocity gradients represent the core envelope solid-body rotation, we estimate the specific angular momentum to be about 2 × 10²¹ cm² s^-1, similar to the low-mass star-forming cores. Together with the previous finding of subsonic motions in G035.39, our results demonstrate high levels of similarity between kinematics of a high-mass star-forming IRDC and the low-mass star formation regime.