Cloud-Cloud Collision: Formation of Hub-Filament Systems and Associated Gas Kinematics; Mass-collecting cone: A new signature of Cloud-Cloud Collision

TL;DR

This study uses magneto-hydrodynamic simulations to demonstrate how cloud-cloud collisions can form hub-filament systems and drive gas kinematics, revealing new signatures like mass-collecting cones that aid in identifying such events.

Contribution

It provides a detailed simulation-based explanation of how cloud-cloud collisions lead to hub-filament system formation and introduces the mass-collecting cone as a new observational signature.

Findings

Cloud-cloud collisions induce filamentary structures within shock-compressed layers.

The formation of hub-filament systems results from combined effects of turbulence, magnetic fields, and gravity.

Mass-collecting cones serve as a new signature for identifying cloud-cloud collision events.

Abstract

Massive star-forming regions (MSFRs) are commonly associated with hub-filament systems (HFSs) and sites of cloud-cloud collision (CCC). Recent observational studies of some MSFRs suggest a possible connection between CCC and the formation of HFSs. To understand this connection, we analyzed the magneto-hydrodynamic simulation data from Inoue et al. (2018). This simulation involves the collision of a spherical turbulent molecular cloud with a plane-parallel sea of dense molecular gas at a relative velocity of about 10 km/s. Following the collision, the turbulent and non-uniform cloud undergoes shock compression, rapidly developing filamentary structures within the compressed layer. We found that CCC can lead to the formation of HFSs, which is a combined effect of turbulence, shock compression, magnetic field, and gravity. The collision between the cloud components shapes the filaments into a cone and drives inward flows among them. These inward flows merge at the vertex of the cone, rapidly accumulating high-density gas, which can lead to the formation of massive star(s). The cone acts as a mass-collecting machine, involving a non-gravitational early process of filament formation, followed by gravitational gas attraction to finalize the HFS. The gas distribution in the position-velocity (PV) and position-position spaces highlights the challenges in detecting two cloud components and confirming their complementary distribution if the colliding clouds have a large size difference. However, such CCC events can be confirmed by the PV diagrams presenting gas flow toward the vertex of the cone, which hosts gravitationally collapsing high-density objects, and by the magnetic field morphology curved toward the direction of the collision.