ATOMS: ALMA Three-millimeter Observations of Massive Star-forming
  regions-IX. A pilot study towards IRDC G034.43+00.24 on multi-scale
  structures and gas kinematics
  We present a comprehensive study of the gas kinematics associated with
density structures at different spatial scales in the filamentary infrared dark
cloud, G034.43+00.24 (G34). This study makes use of the H13CO+ (1-0) molecular
line data from the ALMA Three-millimeter Observations of Massive Star-forming
regions (ATOMS) survey, which has spatial and velocity resolution of 0.04 pc
and 0.2 km/s, respectively. Several tens of dendrogram structures have been
extracted in the position-position-velocity space of H13CO+, which include 21
small-scale leaves and 20 larger-scale branches. Overall, their gas motions are
supersonic but they exhibit the interesting behavior where leaves tend to be
less dynamically supersonic than the branches. For the larger-scale, branch
structures, the observed velocity-size relation (i.e., velocity
variation/dispersion versus size) are seen to follow the Larson scaling
exponent while the smaller-scale, leaf structures show a systematic deviation
and display a steeper slope. We argue that the origin of the observed
kinematics of the branch structures is likely to be a combination of turbulence
and gravity-driven ordered gas flows. In comparison, gravity-driven chaotic gas
motion is likely at the level of small-scale leaf structures. The results
presented in our previous paper and this current follow-up study suggest that
the main driving mechanism for mass accretion/inflow observed in G34 varies at
different spatial scales. We therefore conclude that a scale-dependent combined
effect of turbulence and gravity is essential to explain the star-formation
processes in G34.
