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arXiv · 1706.07164

CO observations of the molecular gas in the galactic HII region Sh2-48; Evidence for cloud-cloud collision as a trigger of high-mass star formation

Kazufumi Torii·Yusuke Hattori·Mitsuhiro Matsuo·Shinji Fujita·Atsushi Nishimura·Mikito Kohno·Mika Kuriki·Yuya Tsuda·Tetsuhiro Minamidani·Tomofumi Umemoto·Nario Kuno·Satoshi Yoshiike·Akio Ohama·Kengo Tachihara·Yasuo Fukui·Kazuhiro Shima·Asao Habe·Thomas J. Haworth
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Abstract

Sh2-48 is a Galactic HII region located at 3.8 kpc with an O9.5-type star identified at its center. As a part of the FOREST Unbiased Galactic plane Imaging survey using the Nobeyama 45-m telescope (FUGIN) project, we obtained the CO J=1-0 dataset for a large area of Sh2-48 at a spatial resolution of 21"(~0.4 pc), which we used to find a molecular cloud with a total molecular mass of ~3.8x10^4 Mo associated with Sh2-48. The molecular cloud has a systematic velocity shift within a velocity range ~42-47 km/s . On the lower velocity side the CO emission spatially corresponds with the bright 8 μm filament at the western rim of Sh2-48, while the CO emission at higher velocities is separated at the eastern and western sides of the 8μm filament. This velocity change forms V-shaped, east-west-oriented feature on the position-velocity diagram. We found that these lower and higher-velocity components are, unlike the infrared and radio continuum data, physically associated with Sh2-48. To interpret the observed V-shaped velocity distribution, we assessed a cloud-cloud collision scenario and found from a comparison between the observations and simulations that the velocity distribution is an expected outcome of a collision between a cylindrical cloud and a spherical cloud, with the cylindrical cloud corresponding to the lower-velocity component, and the two separated components in the higher-velocity part interpretable as the collision-broken remnants of the spherical cloud. Based on the consistency of the ~1.3Myr estimated formation timescale of the HII region with that of the collision, we concluded that the high-mass star formation in Sh2-48 was triggered by the collision.

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Kazufumi Torii, Yusuke Hattori, Mitsuhiro Matsuo, Shinji Fujita, Atsushi Nishimura, Mikito Kohno, Mika Kuriki, Yuya Tsuda, Tetsuhiro Minamidani, Tomofumi Umemoto, Nario Kuno, Satoshi Yoshiike, Akio Ohama, Kengo Tachihara, Yasuo Fukui, Kazuhiro Shima, Asao Habe, Thomas J. Haworth. 2018-08-01. CO observations of the molecular gas in the galactic HII region Sh2-48; Evidence for cloud-cloud collision as a trigger of high-mass star formation. https://doi.org/10.1093/pasj%2Fpsy098

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