IC 5146 Dark Streamer: The First Reliable Candidate of Edge Collapse, Hub-filament Systems, and Intertwined Sub-filaments

The paper presents an analysis of multiwavelength data of a nearby star-forming site, the IC 5146 dark streamer (d ∼ 600 pc), which has been treated as a single and long filament, fl. Two hub-filament systems (HFSs) are known to exist toward the eastern and the western ends of fl. Earlier published results favor simultaneous evidence of HFSs and end-dominated collapse (EDC) in fl. A Herschel column density map (resolution ∼13.″5) reveals two intertwined sub-filaments (i.e., fl-A and fl-B) toward fl, displaying a nearly double helix-like structure. This picture is also supported by the C¹⁸O(3-2) emission. The fray and fragment scenario may explain the origin of intertwined sub-filaments. In the direction of fl, two cloud components around 2 and 4 km s⁻¹ are depicted using ¹³CO(1-0) and C¹⁸O(1-0) emission and are connected in velocity space. The HFSs are spatially found at the overlapping areas of these cloud components and can be explained by the cloud-cloud collision scenario. Nonthermal gas motion in fl with a larger Mach number is found. The magnetic field position angle measured from the filament’s long axis shows a linear trend along the filament. This signature is confirmed in the other nearby EDC filaments, presenting a more quantitative confirmation of the EDC scenario. Based on our observational outcomes, we witness multiple processes operational in the IC 5146 streamer. Overall, the streamer can be recognized as the first reliable candidate for edge collapse, HFSs, and intertwined sub-filaments.