Random gas motions inside sub-parsec scale supercritical filaments
Supercritical gas filaments in molecular clouds host the dense cores in which new stars form. The mechanisms governing their formation and subsequent gas accretion remain poorly understood. In this study, we conduct a statistical analysis of a large sample of sub-parsec supercritical filaments using H13COp J=1-0 data from the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) Survey. We identified velocity-coherent filaments in position-position-velocity (PPV) space and systematically examined velocity gradients both along and perpendicular to their skeletons. Our analysis uncovers a remarkable result: at scales of ~ 0.1-1 pc, the local velocity gradients within these supercritical filaments show no preferred alignment with the filament skeletons and exhibit no correlation with the local gravitational field. This random orientation suggests the presence of chaotic gas motions deep inside these dense structures. These findings may indicate that turbulence-rather than gravity-dominates gas dynamics and structural evolution at small scales, even in regions on the verge of star formation, challenging the paradigm of gravity-dominated structure formation within molecular clouds. This scenario should be further tested by more state-of-the-art simulations. This study offers key observational insights into the roles of turbulence and gravity in establishing the initial conditions for star formation.