# Multicomponent kinematics in a massive filamentary IRDC

## TL;DR

This study investigates the complex velocity structures and motions within dense filaments of a massive infrared dark cloud, revealing similarities with low-mass star formation processes and providing detailed kinematic measurements.

## Contribution

It introduces a detailed analysis of multicomponent kinematics in a high-mass IRDC using combined VLA and GBT data, highlighting the presence of coherent structures and comparing their motions to low-mass cores.

## Key findings

- Identified seven extended velocity-coherent components in the IRDC.
- Found velocity gradients consistent with core rotation and similar to low-mass cores.
- Discovered ammonia line widths are narrower than N2H+ lines, contrary to expectations.

## Abstract

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.