ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions - VI. Hierarchical fragmentation and gas dynamics in IRDC G034.43+00.24

We present new observations of 3mm continuum and molecular lines from the ATOMS survey towards two massive protostellar clumps, MM1 and MM2, located in the filamentary infrared dark cloud (IRDC), G034.43+00.24 (G34). The lines observedare the tracers of either dense gas (e.g., HCO+/H13CO+ J=1–0) or outflows (e.g., CS J=2–1). The most complete picture to date of seven cores in MM1 is revealed by dust continuum emission, whereas only two cores are identified in MM2 due to the incomplete coverage of the IRDC in the ATOMS survey. These cores are found to be gravitationally bound, with virial parameter, vir < 2. At least four outflows are identified in MM1 with a total outflowing mass of 45M, and a total energyof 1 1047 ergs, typical of outflows from a B0-type star. Evidence of hierarchical fragmentation, where turbulence dominates over thermal pressure, is observed at both the cloud and the clump scales. This could be linked to the scale-dependent, dynamical mass inflow/accretion on clump and core scales.We therefore suggest that the G34 cloud could be undergoing a dynamical mass inflow/accretion process linked to the multi-scale fragmentation, which leads to the sequential formation of fragments of the initial cloud, clumps, and ultimately dense cores, the sites of star formation.