Galactic 'Snake' IRDC G11.11-0.12: A site of multiple hub-filament systems and colliding filamentary clouds

To probe star formation processes, we present a multiscale and multiwavelength investigation of the 'Snake' nebula/infrared dark cloud G11.11-0.12 (hereafter, G11; length ∼27 pc). Spitzer images hint at the presence of subfilaments (in absorption), and reveal four infrared-dark hub-filament system (HFS) candidates (extent < 6 pc) towards G11, where massive clumps (> 500 M) and protostars are identified. The 13CO(2-1), C18O(2-1), and NH3(1,1) line data reveal a noticeable velocity oscillation towards G11, as well as its left part (or part-A) around Vlsr of 31.5 km s-1, and its right part (or part-B) around Vlsr of 29.5 km s-1. The common zone of these cloud components is investigated towards the centre of G11 housing one HFS. Each cloud component hosts two subfilaments. In comparison to part-A, more APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) clumps are observed towards part-B. The JWST near-infrared images discover one infrared-dark HFS candidate (extent ∼0.55 pc) around the massive protostar G11P1 (i.e. G11P1-HFS). Hence, the infrared observations reveal multiple infrared-dark HFS candidates at multiscale in G11. The Atacama Large Millimeter/submillimeter Array (ALMA) 1.16-mm continuum map shows multiple finger-like features (extent ∼3500-10 000 au) surrounding a dusty envelope-like feature (extent ∼18 000 au) towards the central hub of G11P1-HFS. Signatures of forming massive stars are found towards the centre of the envelope-like feature. The ALMA H13CO+ line data show two cloud components with a velocity separation of ∼2 km s-1 towards G11P1. Overall, the collision process, the 'fray and fragment' mechanism, and the 'global non-isotropic collapse' scenario seem to be operational in G11.