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We present new continuum and molecular line data from the ALMAThree-millimeter Observations of Massive Star-forming regions (ATOMS) surveyfor the two protoclusters, G12.42+0.50 and G19.88-0.53. The 3 mm continuum mapsreveal seven cores in each of the two globally contracting protoclusters. Thesecores satisfy the radius-mass relation and the surface mass density criteriafor high-mass star formation. Similar to their natal clumps, the virialanalysis of the cores suggests that they are undergoing gravitational collapse($\rm \alpha_{vir} << 2$). The clump to core scale fragmentation isinvestigated and the derived core masses and separations are found to beconsistent with thermal Jeans fragmentation. We detect large-scale filamentarystructures with velocity gradients and multiple outflows in both regions.Dendrogram analysis of the H$^{13}$CO$^{+}$ map identifies several branch andleaf structures with sizes $\sim$ 0.1 and 0.03 pc, respectively. The supersonicgas motion displayed by the branch structures is in agreement with the Larsonpower-law indicating that the gas kinematics at this spatial scale is driven byturbulence. The transition to transonic/subsonic gas motion is seen to occur atspatial scales of $\sim$0.1 pc indicating the dissipation of turbulence. Inagreement with this, the leaf structures reveal gas motions that deviate fromthe slope of Larson's law. From the large-scale converging filaments to thecollapsing cores, the gas dynamics in G12.42+0.50 and G19.88-0.53 showscale-dependent dominance of turbulence and gravity and the combination ofthese two driving mechanisms needs to be invoked to explain massive starformation in the protoclusters.

monthly notices of the royal astronomical society

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming  regions -- XII: Fragmentation and multi-scale gas kinematics in protoclusters  G12.42+0.50 and G19.88-0.53