ALMA CO observations of a giant molecular cloud in M 33: Evidence for high-mass star formation triggered by cloud–cloud collisions

• Published in: Publications of the Astronomical Society of Japan 2021-01, Vol.73 (Supplement_1), p.S62-S74
• Main Authors: Sano, Hidetoshi, Tsuge, Kisetsu, Tokuda, Kazuki, Muraoka, Kazuyuki, Tachihara, Kengo, Yamane, Yumiko, Kohno, Mikito, Fujita, Shinji, Enokiya, Rei, Rowell, Gavin, Maxted, Nigel, Filipović, Miroslav D, Knies, Jonathan, Sasaki, Manami, Onishi, Toshikazu, Plucinsky, Paul P, Fukui, Yasuo
• Format: Article
• Language: English
• ISSN: 0004-6264; 2053-051X
• DOI: 10.1093/pasj/psaa045

Abstract We report the first evidence for high-mass star formation triggered by collisions of molecular clouds in M 33. Using the Atacama Large Millimeter/submillimeter Array, we spatially resolved filamentary structures of giant molecular cloud 37 in M 33 using 12CO(J = 2–1), 13CO(J = 2–1), and C18O(J = 2–1) line emission at a spatial resolution of ∼2 pc. There are two individual molecular clouds with a systematic velocity difference of ∼6 km s−1. Three continuum sources representing up to ∼10 high-mass stars with spectral types of B0V–O7.5V are embedded within the densest parts of molecular clouds bright in the C18O(J = 2–1) line emission. The two molecular clouds show a complementary spatial distribution with a spatial displacement of ∼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 H ii regions. Our new finding in M 33 indicates that cloud–cloud collision is a promising process for triggering high-mass star formation in the Local Group.