High-resolution APEX/LAsMA $^{12}$CO and $^{13}$CO (3-2) observation of the G333 giant molecular cloud complex : III. Decomposition of molecular clouds into multi-scale hub-filament structures

TL;DR

This study uses high-resolution observations to decompose the G333 molecular cloud complex into multi-scale hub-filament systems, revealing their properties, dynamics, and potential evolutionary sequence, advancing understanding of molecular cloud structure and star formation.

Contribution

It introduces a method to identify and characterize multi-scale hub-filament structures in molecular clouds, highlighting their role in gravitational collapse and star formation.

Findings

HFs have higher density contrast and larger masses than non-HFs.

Velocity gradients indicate gas inflow towards hubs.

An evolutionary sequence from non-HFs to HFs is suggested.

Abstract

We decomposed the G333 complex and the G331 giant molecular cloud into multi-scale hub-filament systems (HFs) using the high-resolution $^{13}$CO (3$-$2) data from LAsMA observations. We employed the filfinder algorithm to identify and characterize filaments within HFs. Compared with non-HFs, HFs have significantly higher density contrast, larger 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. Currently, non-HFs lack a distinct gravitational focusing process that would result in significant density contrast. The density contrast can effectively measure the extent of gravitational collapse and the strength of the gravitational center of the structure that definitively shape the hub-filament morphology. Combined with the kinematic evidence in 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. Actually, clumps in molecular clouds are equivalent to the hubs. The network structure of molecular clouds can naturally explain that feedback from protoclusters does not significantly change the kinematic properties of the surrounding embedded dense gas structures, as concluded in our previous studies.