ALMA CO Observations of a Giant Molecular Cloud in M33: Evidence for High-Mass Star Formation Triggered by Cloud-Cloud Collisions

• Published in: arXiv.org 2020-06
• Main Authors: Sano, Hidetoshi, Tsuge, Kisetsu, Tokuda, Kazuki, Muraoka, Kazuyuki, Tachihara, Kengo, Yamane, Yumiko, Kohno, Mikito, Fujita, Shinji, Enokiya, Rei, Rowell, Gavin, Maxted, Nigel, Filipovic, Miroslav D, Knies, Jonathan, Sasaki, Manami, Onishi, Toshikazu, Plucinsky, Paul P, Fukui, Yasuo
• Format: Article
• Language: English
• Subjects: Astrochemistry; Collisions; Emission; Massive stars; Molecular clouds; Radio telescopes; Spatial distribution; Spatial resolution; Spiral galaxies; Star & galaxy formation; Star formation
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1908.08404

We report the first evidence for high-mass star formation triggered by collisions of molecular clouds in M33. Using the Atacama Large Millimeter/submillimeter Array, we spatially resolved filamentary structures of giant molecular cloud 37 in M33 using \(^{12}\)CO(\(J\) = 2-1), \(^{13}\)CO(\(J\) = 2-1), and C\(^{18}\)O(\(J\) = 2-1) line emission at a spatial resolution of \(\sim\)2 pc. There are two individual molecular clouds with a systematic velocity difference of \(\sim\)6 km s\(^{-1}\). Three continuum sources representing up to \(\sim\)10 high-mass stars with the spectral types of B0V-O7.5V are embedded within the densest parts of molecular clouds bright in the C\(^{18}\)O(\(J\) = 2-1) line emission. The two molecular clouds show a complementary spatial distribution with a spatial displacement of \(\sim\)6.2 pc, and show a V-shaped structure in the position-velocity diagram. These observational features traced by CO and its isotopes are consistent with those in high-mass star-forming regions created by cloud-cloud collisions in the Galactic and Magellanic Cloud HII regions. Our new finding in M33 indicates that the cloud-cloud collision is a promising process to trigger high-mass star formation in the Local Group.