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arXiv · 1706.05871

High-mass star formation possibly triggered by cloud-cloud collision in the HII region RCW 34

Katsuhiro Hayashi·Hidetoshi Sano·Rei Enokiya·Kazufumi Torii·Yusuke Hattori·Mikito Kohno·Shinji Fujita·Atsushi Nishimura·Akio Ohama·Hiroaki Yamamoto·Kengo Tachihara·Yutaka Hasegawa·Kimihiro Kimura·Hideo Ogawa·Yasuo Fukui
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Abstract

We report a possibility that the high-mass star located in the HII 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=$3-2 lines toward RCW 34 were measured by using the NANTEN2 and ASTE telescopes. We found two clouds with the velocity ranges of 0-10 km s$^{-1}$ and 10-14 km s$^{-1}$. Whereas the former cloud as massive as ~2.7 x 10$^{4}$ Msun has a morphology similar to the ring-like structure observed in the infrared wavelengths, the latter cloud with the mass of ~10$^{3}$ Msun, 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 types of O8.5V is located near the boundary of the two clouds. The line intensity ratio of $^{12}$CO $J=$3-2 / $J=$2-1 yields high values (~1.5) in the neighborhood of the high-mass star, suggesting that these clouds are associated with the massive star. We also confirmed that the obtained position-velocity diagram shows a similar distribution with that derived by a numerical simulation of the supersonic collision of two clouds. Using the relative velocity between the two clouds (~5 km s$^{-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 ~0.2 Myr via a triggering of cloud-cloud collision.

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Katsuhiro Hayashi, Hidetoshi Sano, Rei Enokiya, Kazufumi Torii, Yusuke Hattori, Mikito Kohno, Shinji Fujita, Atsushi Nishimura, Akio Ohama, Hiroaki Yamamoto, Kengo Tachihara, Yutaka Hasegawa, Kimihiro Kimura, Hideo Ogawa, Yasuo Fukui. 2017-11-10. High-mass star formation possibly triggered by cloud-cloud collision in the HII region RCW 34. https://doi.org/10.1093/pasj%2Fpsx141

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