Automated extraction of peculiar velocity structures in Aquila Rift with the FilFinder algorithm

Abstract To develop a systematic method for extracting peculiar velocity structures in molecular clouds with unusually large line widths for their sizes, we applied the FilFinder algorithm to running-mean-subtracted position–velocity diagrams of the Aquila Rift region, a nearby star-forming complex that includes W 40 and Serpens South, using the CO J = 1–0 data obtained by the NRO Star Formation Legacy Project. Based on this automatic approach without bias to the candidate excitation sources, we identified 83 groups of significant subparsec-scale peculiar velocity structures. Among them, 31 are associated with molecular outflows; 8 of them are newly identified as candidate outflows or outflow-like features, including 2 that correspond to the blue lobe counterpart of a previously known red lobe and 6 that have no known excitation sources. For the remaining 52 groups, we also confirm some previously reported marginal outflow detections, while finding others to be insignificant. We identified several other types of small-scale peculiar velocity structures. A total of 10 isolated compact structures tend to show low ${\rm CO/^{13}CO}$ ratios and are preferentially located at the interface with the shell of the H ii region, suggesting that they are fragments of molecular gas accelerated and displaced by the expanding shell. A total of 15 compact structures found in the 14 km s$^{-1}$ component are located near the edges of the spatially extended moderately broad emission, likely tracing the boundaries of interacting regions. In the 40 km s$^{-1}$ component, we identified 14 small-scale peculiar velocity structures that correspond to the velocity structure of the main cloud, suggesting a possible interaction between the 40 km s$^{-1}$ cloud and the main cloud. The remaining 13 groups are classified as other structures. These results demonstrate that automatic extraction of peculiar velocity structures using the FilFinder algorithm is a powerful tool for identifying perturbed molecular gas in an unbiased and systematic manner.