Study of HI Turbulence in the SMC Using Multipoint Structure Functions

Turbulence in the interstellar medium (ISM) plays an important role in many physical processes, including forming stars and shaping complex ISM structures. In this work, we investigate the H I turbulence properties of the Small Magellanic Cloud (SMC) to reveal what physical mechanisms drive the turbulence and at what scales. Using high-resolution H I data from the Galactic ASKAP survey and multipoint structure functions (SFs), we perform a statistical analysis of H I turbulence in 34 subregions of the SMC. The two-point SFs tend to show a linear trend, and their slope values are relatively uniform across the SMC, suggesting that large-scale structures exist and are dominant in the two-point SFs. On the other hand, seven-point SFs enable us to probe small-scale turbulence by removing large-scale fluctuations, which is difficult to achieve with the two-point SFs. In the seven-point SFs, we find break features at scales of 34─84 pc, with a median scale of ∼50 pc. This result indicates the presence of small-scale turbulence fluctuations in the SMC and quantifies their scale. In addition, we find strong correlations between the slope values of the seven-point SFs and stellar-feedback-related quantities (e.g., Hα intensity, the number of young stellar objects, and the number of H I shells), suggesting that stellar feedback may affect the small-scale turbulence properties of the H I gas in the SMC. Lastly, the estimated sonic Mach numbers across the SMC are subsonic, which is consistent with the fact that the H I gas of the SMC primarily consists of a warm neutral medium.