Warm and Dense Molecular Gas in the N 159 Region: 12CO J = 4–3 and 13CO J = 3–2 Observations with NANTEN2 and ASTE

• Published in: Publications of the Astronomical Society of Japan 2010-02, Vol.62 (1), p.51-67
• Main Authors: Mizuno, Yoji, Kawamura, Akiko, Onishi, Toshikazu, Minamidani, Tetsuhiro, Muller, Erik, Yamamoto, Hiroaki, Hayakawa, Takahiro, Mizuno, Norikazu, Mizuno, Akira, Stutzki, Jürgen, Pineda, Jorge L., Klein, Uli, Bertoldi, Frank, Koo, Bon-Chul, Rubio, Monica, Burton, Michael, Benz, Arnold, Ezawa, Hajime, Yamaguchi, Nobuyuki, Kohno, Kotaro, Hasegawa, Tetsuo, Tatematsu, Ken’ichi, Ikeda, Masafumi, Ott, Jürgen, Wong, Tony, Hughes, Annie, Meixner, Margaret, Indebetouw, Remy, Gordon, Karl D., Whitney, Barbara, Bernard, Jean-Philippe, Fukui, Yasuo
• Format: Article
• Language: English
• ISSN: 0004-6264; 2053-051X
• DOI: 10.1093/pasj/62.1.51

New $^{12}$ CO $J =$ 4–3 and $^{13}$ CO $J =$ 3–2 observations of the N 159 region, an active site of massive star formation in the Large Magellanic Cloud, have been made with the NANTEN2 and ASTE submillimeter telescopes, respectively. The $^{12}$ CO $J =$ 4–3 distribution is separated into three clumps, each associated with N 159 W, N 159 E, and N 159 S. These new measurements toward the three clumps are used in coupled calculations of molecular rotational excitation and line radiation transfer, along with other transitions of the $^{12}$ CO $J =$ 1–0, $J =$ 2–1, $J =$ 3–2, and $J =$ 7–6 as well as the isotope transitions of $^{13}$ CO $J =$ 1–0, $J =$ 2–1, $J =$ 3–2, and $J =$ 4–3. The $^{13}$ CO $J =$ 3–2 data were newly taken for the present work. The temperatures and densities were found to be $\sim$ 70 80 K and $\sim$ 3 $\times$ 10 $^{3}$ cm $^{-3}$ in N 159 W and N 159 E, and $\sim$ 30 K and $\sim$ 1.6 $\times$ 10 $^{3}$ cm $^{-3}$ in N 159 S. These results were compared with the star-formation activity based on data of young stellar clusters and HII regions as well as midinfrared emission obtained with the Spitzer MIPS. The N 159 E clump is associated with cluster(s) embedded, as observed at 24 $\mu$ m by the Spitzer MIPS, and the derived high temperature, 80 K, is interpreted as being heated by these sources. The N 159 E clump is likely to be responsible for a dark lane in a large H II region by dust extinction. On the other hand, the N 159 W clump is associated with clusters embedded mainly toward the eastern edge of the clump only. These clusters show offsets of 20 ^{\prime\prime}$ –40 ^{\prime\prime}$ from the $^{12}$ CO $J =$ 4–3 peak, and are probably responsible for heating indicated by the derived high temperature, 70 K. The N 159 W clump exhibits no sign of star formation toward the $^{12}$ CO $J =$ 4–3 peak position and its western region that shows enhanced $R_{4-3/1-0}$ and $R_{3-2/1-0}$ ratios. We therefore suggest that the N 159 W peak represents a pre-star-cluster core of $\sim$ 10 $^{5} M_{\odot}$ which deserves further detailed studies. The N 159 S clump shows little sign of star formation, as is consistent with the lower temperature, 30 K, and has a somewhat lower density than N 159 W and N 159 E. The N 159 S clump is also a candidate for future star formation.