Large-scale NH3 observations toward the galactic star-forming regions I. W 51 molecular cloud complex

Kazuo Sorai, Asao Habe, Hiroyuki Nishitani, Keita Hosaka, Yoshimasa Watanabe, Shinichi Miwa, Yukie Ohishi, Kazuhito Motogi, Tetsuhiro Minamidani, Johta Awano, Sakurako Sumida, Yoshiaki Fukuya, Ryosuke Uchida, Noboru Kaneko, Masayuki Y. Fujimoto, Yasuhiro Koyama, Moritaka Kimura, Naomasa Nakai

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)

Abstract

Large-area observations of dense molecular gas were made in NH3 (J, K) = (1, 1), (2, 2), and (3, 3) inversion lines with 4′.5 resolution toward the molecular cloud complex of the W 51 region. The observations were a part of a NH3 survey of the Galactic star-forming regions using the Tomakomai 11-m radio telescope. NH3 (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 W 51 B. The rotation temperature was ∼40 K in the central part of the W 51 A complex, while being ∼20 K 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-NH3: 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 ∼ 10 pc, and the proceeding transformation has made the ortho-to-para ratio lower.

Original languageEnglish
Pages (from-to)1285-1296
Number of pages12
JournalPublications of the Astronomical Society of Japan
Volume60
Issue number6
DOIs
Publication statusPublished - 2008
Externally publishedYes

Keywords

  • ISM: Clouds
  • ISM: Individual (W 51)
  • Stars: Formation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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