MOLECULAR CLOUDS IN THE TRIFID NEBULA M20: POSSIBLE EVIDENCE FOR A CLOUD-CLOUD COLLISION IN TRIGGERING THE FORMATION OF THE FIRST GENERATION STARS
- Department of Physics and Astrophysics, Nagoya University, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan)
- Department of Astrophysics, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531 (Japan)
- Solar-Terrestrial Environment Laboratory, Nagoya University, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan)
A large-scale study of the molecular clouds toward the Trifid Nebula, M20, has been made in the J = 2-1 and J = 1-0 transitions of {sup 12}CO and {sup 13}CO. M20 is ionized predominantly by an O7.5 star HD164492. The study has revealed that there are two molecular components at separate velocities peaked toward the center of M20 and that their temperatures-30-50 K as derived by a large velocity gradient analysis-are significantly higher than the 10 K of their surroundings. We identify the two clouds as the parent clouds of the first generation stars in M20. The mass of each cloud is estimated to be {approx}10{sup 3} M{sub sun} and their separation velocity is {approx}8 km s{sup -1} over {approx}1-2 pc. We find that the total mass of stars and molecular gas in M20 is less than {approx}3.2 x 10{sup 3} M{sub sun}, which is too small by an order of magnitude to gravitationally bind the system. We argue that the formation of the first generation stars, including the main ionizing O7.5 star, was triggered by the collision between the two clouds in a short timescale of {approx}1 Myr, a second example alongside Westerlund 2, where a super-star cluster may have been formed due to cloud-cloud collision triggering.
- OSTI ID:
- 21582930
- Journal Information:
- Astrophysical Journal, Vol. 738, Issue 1; Other Information: DOI: 10.1088/0004-637X/738/1/46; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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