CO Observations of the SMC-N66 H ii Region with ALMA: Properties of Clumps Along Filamentary Molecular Clouds and Possible Expansion Motion

The star-forming region N66, as a host of the majority of OB stars in the Small Magellanic Cloud, provides a unique opportunity to enhance our understanding of the triggers of high-mass star formation. We investigate the properties of the molecular cloud in N66 using the ¹²CO(1-0) data obtained with the Atacama Large Millimeter/submillimeter Array. A cloud decomposition analysis identified 165 independent cloud structures and substructures. The size-linewidth scaling relation for the entire region exhibits an index of 0.49, indicating that the region is in a state of virial equilibrium. In contrast, a detailed analysis of the central N66 region revealed a size-line width scaling relation with an index of 0.75, suggesting that distinct factors are influencing the dynamics of this central area. Averaging the spectra in the central N66 region revealed three distinct velocity peaks at 145, 152, and 160 km s⁻¹, indicating that some kinds of interactions are occurring within the cloud. The analysis of the position-velocity diagrams in the central region revealed a ring-like structure, indicating the presence of an expanding bubble. The bubble exhibits supersonic characteristics, with an expansion velocity of v exp ≈ 11 km s⁻¹, and an overall systemic velocity of v_sys ≈ 151 km s⁻¹. The radius is estimated to be in the range of r ≈ [9.8−12.9] ± 0.5 pc and is approximately 1.2 Myr old.