Molecular clouds in the NGC6334 and NGC6357 region; Evidence for a 100 pc-scale cloud-cloud collision triggering the Galactic mini-starbursts

摘要

We carried out new CO ($J=$1-0, 2-1 and 3-2) observations with NANTEN2 andASTE in the region of the twin Galactic mini-starbursts NGC6334 and NGC6357. Wedetected two velocity molecular components of 12 km s$^{-1}$ velocityseparation, which is continuous over 3 degrees along the plane. In NGC6334 thetwo components show similar two-peaked intensity distributions toward the youngHII regions and are linked by a bridge feature. In NGC6357 we found spatiallycomplementary distribution between the two velocity components as well as abridge feature in velocity. Based on these results we hypothesize that the twoclouds in the two regions collided with each other during the last $\sim$1 Myrand triggered formation of the starbursts over $\sim$100 pc along the Galacticplane. We suggest that the formation of the starbursts happened toward thecollisional region with initial high molecular column densities. For NGC6334 wepresent a scenario which includes spatial variation of the colliding epoch dueto non-uniform cloud separation. The scenario possibly explains the apparentage difference among the young O stars in NGC6334 raging from 10$^4$ yrs to10$^6$ yrs, the latest collision happened within 10$^5$ yrs toward the youngeststars in NGC6334 I and I(N) which exhibit molecular outflows without HIIregions. For NGC6357 the O stars were formed a few Myrs ago, and the clouddispersal by the O stars is significant. We conclude that cloud-cloud collisionoffers a possible explanation of the min-starburst over a 100-pc scale.