Large-Scale NH3 Observations toward the Galactic Star-Forming Regions I. W 51 Molecular Cloud Complex

• Published in: Publications of the Astronomical Society of Japan Vol. 60; no. 6; pp. 1285 - 1296
• Main Authors: Sorai, Kazuo, Habe, Asao, Nishitani, Hiroyuki, Hosaka, Keita, Watanabe, Yoshimasa, Miwa, Shinichi, Ohishi, Yukie, Motogi, Kazuhito, Minamidani, Tetsuhiro, Awano, Johta, Sumida, Sakurako, Fukuya, Yoshiaki, Uchida, Ryosuke, Kaneko, Noboru, Fujimoto, Masayuki Y., Koyama, Yasuhiro, Kimura, Moritaka, Nakai, Naomasa
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford University Press 25.12.2008
• Subjects: stars: formation; ISM: clouds; ISM: individual (W51)
• ISSN: 0004-6264; 2053-051X
• DOI: 10.1093/pasj/60.6.1285

Large-area observations of dense molecular gas were made in NH $_{3}$ ( $J$ , $K$ ) $=$ (1, 1), (2, 2), and (3, 3) inversion lines with 4'.5 resolution toward the molecular cloud complex of the W51 region. The observations were a part of a NH $_{3}$ survey of the Galactic star-forming regions using the Tomakomai 11-m radio telescope. NH $_{3}$ ( $J$ , $K$ ) $=$ (1, 1) and (2, 2) emission was detected in the W51 A and B complexes, while the detection of ( $J$ , $K$ ) $=$ (2, 2) emission was marginal in W51 B. The rotation temperature was $\sim$ 40K in the central part of the W51 A complex, while being $\sim$ 20K in the other positions. A weak correlation is found that the ortho-to-para ratio decreases with increasing the rotation temperature, the far-infrared luminosity and the index of the star-formation efficiency. This tendency is explained if star formation has continued for more than the time scale of the transformation between ortho- and para-NH $_{3}$ : active star formation on a large scale, such as the interaction of molecular clouds with a spiral arm, has made the molecular gas warmer, even in a scale of $\sim$ 10pc, and the proceeding transformation has made the ortho-to-para ratio lower.