Author(s): , , , , ,
Institution(s): 1. Nagoya University
Since 2009, several molecular line observations toward the galactic high-mass star forming regions have indicated that cloud-cloud collisions (CCC) play an important role in forming high-mass stars; for example, super star clusters Westerlund2, NGC3603, and RCW38 (Furukawa et al. 2009; Fukui et al. 2014, 2015) and small galactic HII regions M20 and RCW120 which are each excited by a single O star (Torii et al. 2011, 2015). Using the NANTEN2 4-m telescope situated at Atacama, Chile, we have completed a large-scale molecular line mapping toward young galactic starburst regions NGC6334 and NGC6357. The two regions have several clusetrs which are rich in O stars having 30-100 MSun and are suggested to be physically connected with each other, although they are separated by 100 pc. Our new CO observations show that two molecular cloud complexes are distributed toward NGC6334 and NGC6357 at two different velocities, -3 km/s and -18 km/s. They have filamentary distributions elongated for over 100 pc nearly parallel to the galactic plane. The -3km/s complex apparently shows morphological agreements with the nebulosity in NGC6334 and NGC6357, and the -18km/s complex shows complementary distributions with the -3 km/s complex especially toward the O stars. Furthermore, intermediate velocity features which connect the two complexes are seen toward the same direction. These observational signatures indicate the physical association of the two cloud complexes with NGC6334 and NGC6357. We postulate a scenario that a collision between the two filamentary cloud complexes with a colliding velocity ~15 km/s triggered high-mass star formation in NGC6334 and NGC6357. The timescale of the collision, thus the high-mass star formation, is estimated to be less than 0.5 Myrs, which corresponds to a mass accretion rate up to 2×10-4 MSun/yr. Previous known CCC origin objects are the ones in which high-mass star were formed at a very limited volume less than 1pc3. In contrast, the CCC in NGC6334 and NGC6357 are extended for over 100 pc. NGC6334 and NGC6357 provide a unique site to study the interaction between the galactic arms.