Multicomponent kinematics in a massive filamentary IRDC
  To probe the initial conditions for high-mass star and cluster formation, we
investigate the properties of dense filaments within the infrared dark cloud
G035.39-00.33 (IRDC G035.39) in a combined Very Large Array (VLA) and the Green
Bank Telescope (GBT) 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 km/s/pc and has a
long tail extending into higher values of 1.5 - 2 km/s/pc, and is generally
consistent with those found toward the same cloud in other molecular tracers
and with the values found towards nearby low-mass dense cloud cores at the same
scales. Contrary to observational and theoretical expectations, we find the
non-thermal 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 x 10^21
cm^2/s, 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.
