We report a possibility that the high-mass star located in the H ii region RCW 34 was formed by a triggering induced by a collision of molecular clouds .
Molecular gas distributions of the ^ { 12 } CO and ^ { 13 } CO J = 2-1 , and ^ { 12 } CO J = 3-2 lines in the direction of RCW 34 were measured by using the NANTEN2 and ASTE telescopes .
We found two clouds with the velocity ranges of 0–10 km s ^ { -1 } and 10–14 km s ^ { -1 } .
Whereas the former cloud as massive as \sim 1.4 \times 10 ^ { 4 } { \it M } _ { \odot } has a morphology similar to the ring-like structure observed in the infrared wavelengths , the latter cloud with the mass of \sim 600 { \it M } _ { \odot } , which has not been recognized by previous observations , distributes just likely to cover the bubble enclosed by the other cloud .
The high-mass star with the spectral type of O8.5V is located near the boundary of the two clouds .
The line intensity ratio of ^ { 12 } CO J = 3-2 / J = 2-1 yields high values ( \gtrsim 1.0 ) , suggesting that these clouds are associated with the massive star .
We also confirmed that the obtained position-velocity diagram shows a similar distribution to that derived by a numerical simulation of the supersonic collision of two clouds .
Using the relative velocity between the two clouds ( \sim 5 km s ^ { -1 } ) , the collisional time scale is estimated to be \sim 0.2 Myr with the assumption of the distance of 2.5 kpc .
These results suggest that the high-mass star in RCW 34 was formed rapidly within a time scale of \sim 0.2 Myr via a triggering of cloud-cloud collision .