Formation of the young compact cluster GM 24 triggered by a cloud-cloud collision

Abstract

High-mass star formation is an important step which controls galactic evolution. GM 24 is a heavily obscured star cluster including a single O9 star with more than ∼100 lower-mass stars within a 0.3 pc radius toward (l, b) ∼ (350.5°, 0.96°), close to the Galactic mini-starburst NGC 6334. We found two velocity components associated with the cluster by new observations of ¹²CO J =2-1 emission, whereas the cloud was previously considered to be single. We found that the distribution of the two components of 5 {km}s^-1 separation shows complementary distribution; the two fit well with each other if a relative displacement of 3 pc is applied along the Galactic plane. A position-velocity diagram of the GM 24 cloud is explained by a model based on numerical simulations of two colliding clouds, where an intermediate velocity component created by the collision is taken into account. We estimate the collision time scale to be ∼Myr in projection of a relative motion tilted to the line of sight by 45°. The results lend further support for cloud-cloud collision as an important mechanism of high-mass star formation in the Carina-Sagittarius Arm.