ALMA CO observations of a giant molecular cloud in M 33: Evidence for high-mass star formation triggered by cloud-cloud collisions
Tokuda, Kazuki; Tachihara, Kengo; Sasaki, Manami; Fukui, Yasuo; Onishi, Toshikazu; Sano, Hidetoshi; Filipović, Miroslav D.; Plucinsky, Paul P.; Muraoka, Kazuyuki; Tsuge, Kisetsu; Fujita, Shinji; Kohno, Mikito; Yamane, Yumiko; Rowell, Gavin; Knies, Jonathan; Enokiya, Rei; Maxted, Nigel
Japan, Australia, Germany, United States
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.