Formation of hub-filament structure triggered by a cloud-cloud collision in the W33 complex

Abstract

Hub-filament systems are suggested to be the birth cradles of high-mass stars and clusters, but the formation of hub-filament structure is still unclear. Using FUGIN ¹³CO (1-0), C¹⁸O (1-0) and SEDIGISM ¹³CO (2-1) survey data, we investigate the formation of hub-filament structure in the W33 complex. The W33 complex consists of two colliding clouds, called W33-blue and W33-red. We decompose the velocity structures in W33-blue by fitting multiple velocity components and find a continuous and monotonic velocity field. Virial parameters of Dendrogram structures suggest the dominance of gravity in W33-blue. The strong positive correlation between velocity dispersion and column density indicates that the non-thermal motions in W33-blue may originate from gravitationally driven collapse. These signatures suggest that the filamentary structures in W33-blue result from the gravitational collapse of a compressed layer. However, the large-scale velocity gradient in W33-blue may originate mainly from cloud-cloud collision and feedback of active star formation, instead of filament-rooted longitudinal inflow. From the results observed above, we argue that cloud-cloud collision triggers the formation of hub-filament structures in the W33 complex. Meanwhile, the appearance of multiple-scale hub-filament structures in W33-blue is likely an imprint of the transition from a compressed layer to a hub-filament system.