2025A&A...699A.355Z

We decomposed the G333 complex and the G331 giant molecular cloud into multi-scale hub-filament systems (HFs) using the highresolution ¹³CO (3-2) data from LAsMA observations. We employed the filfinder algorithm to identify and characterize filaments within HFs. Compared with non-HFs, HFs have a significantly higher density contrast, higher masses, and lower virial ratios. Velocity gradient measurements around intensity peaks provide evidence of gas inflow within these structures. There may be an evolutionary sequence from non-HFs to HFs. There is currently no distinct gravitational focusing process for non-HFs that would result in a significant density contrast. The density contrast can effectively measure the extent of gravitational collapse and the strength of the gravitational center of the structure, which definitively shape the hub-filament morphology. Based on the results from this study and the kinematic evidence from our previous studies, we suggest that molecular clouds are network structures formed by the gravitational coupling of multi-scale hub-filament structures. The knots in the networks are the hubs: they are the local gravitational centers and the main star-forming sites. Clumps in molecular clouds are equivalent to the hubs. The network structure of molecular clouds can naturally explain why feedback from protoclusters does not significantly change the kinematic properties of the surrounding embedded dense gas structures, as concluded in our previous studies.