arXiv 1012.50372010-12-22astro-ph.GAastro-ph.CO

大麦云中巨分子云的致密团块：由$^{13}$ CO（$J=3-2$）观测导出的密度和温度

Dense Clumps in Giant Molecular Clouds in the Large Magellanic Cloud: Density and Temperature Derived from $^{13}$CO($J=3-2$) Observations

Tetsuhiro Minamidani, Takanori Tanaka, Yoji Mizuno, Norikazu Mizuno, Akiko Kawamura, Toshikazu Onishi, Tetsuo Hasegawa, Ken'ichi Tatematsu, Tatsuya Takekoshi, K… 展开作者

Tetsuhiro Minamidani, Takanori Tanaka, Yoji Mizuno, Norikazu Mizuno, Akiko Kawamura, Toshikazu Onishi, Tetsuo Hasegawa, Ken'ichi Tatematsu, Tatsuya Takekoshi, Kazuo Sorai, Nayuta Moribe, Kazufumi Torii, Takeshi Sakai, Kazuyuki Muraoka, Kunihiko Tanaka, Hajime Ezawa, Kotaro Kohno, Sungeun Kim, Mónica Rubio, Yasuo Fukui

备注：: 39 pages, 7 figures, 4 tables. Accepted for publication in The Astronomical Journal
DOI：: 10.1088/0004-6256/141/3/73

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摘要：

为了精确测定大麦云云中分子气体的温度和密度，我们利用ASTE 10 m望远镜对9个观测到$^{12}$ CO（$J=3-2$）团簇的峰进行了光学薄$^{13}$ CO（$J=3-2$）跃迁的观测。这些分子团包括巨分子云（GMC）中的I型（没有大质量恒星形成的迹象）、II型（只有HII区域）和III型（有HII区域和年轻星团）。我们检测到$^{13}$ CO（$J=3-2$）发射的所有峰，发现它们的强度是3 - 12倍低于$^{12}$ CO（$J=3-2$）。我们在45 $\arcsec$分辨率下测定了$^{12}$ CO（$J=3-2$）与$^{13}$ CO（$J=3-2$）、$R^{12/13}_{3-2}$以及$^{13}$ CO（$J=3-2$）与$^{13}$ CO（$J=1-0$）、$R^{13}_{3-2/1-0}$的强度比。这些比率用于辐射传输计算，以估计团块的温度和密度。这些团块的参数范围为动力学温度$T\mathrm{_{kin}}$ = 15 - 200 K，分子氢气密度$n(\mathrm{H_2})$ = 8 $\times 10^2$ - 7 $\times 10^3$ cm $^{-3}$。我们证实，较高密度的团块表现出较高的动力学温度，较低密度的团块较低的动力学温度在一个更好的精度比以前的工作。动力学温度和密度增加一般从I型GMC到III型GMC。我们解释说，这种差异反映了恒星形成的分子团的演化趋势。团簇的$R^{13}_{3-2/1-0}$和动力学温度与H $α$通量有很好的相关性，表明分子气体的加热$n(\mathrm{H_2})$ = $10^3$ -- $10^4$ cm $^{-3}$可以用恒星FUV光子来解释。

英文摘要：

In order to precisely determine temperature and density of molecular gas in the Large Magellanic Cloud, we made observations of optically thin $^{13}$CO($J=3-2$) transition by using the ASTE 10m telescope toward 9 peaks where $^{12}$CO($J=3-2$) clumps were previously detected with the same telescope. The molecular clumps include those in giant molecular cloud (GMC) Types I (with no signs of massive star formation), II (with HII regions only), and III (with HII regions and young star clusters). We detected $^{13}$CO($J=3-2$) emission toward all the peaks and found that their intensities are 3 -- 12 times lower than those of $^{12}$CO($J=3-2$). We determined the intensity ratios of $^{12}$CO($J=3-2$) to $^{13}$CO($J=3-2$), $R^{12/13}_{3-2}$, and $^{13}$CO($J=3-2$) to $^{13}$CO($J=1-0$), $R^{13}_{3-2/1-0}$, at 45$\arcsec$ resolution. These ratios were used for radiative transfer calculations in order to estimate temperature and density of the clumps. The parameters of these clumps range kinetic temperature $T\mathrm{_{kin}}$ = 15 -- 200 K, and molecular hydrogen gas density $n(\mathrm{H_2})$ = 8$\times 10^2$ -- 7$\times 10^3$ cm$^{-3}$. We confirmed that the higher density clumps show higher kinetic temperature and that the lower density clumps lower kinetic temperature at a better accuracy than in the previous work. The kinetic temperature and density increase generally from a Type I GMC to a Type III GMC. We interpret that this difference reflects an evolutionary trend of star formation in molecular clumps. The $R^{13}_{3-2/1-0}$ and kinetic temperature of the clumps are well correlated with H$α$ flux, suggesting that the heating of molecular gas $n(\mathrm{H_2})$ = $10^3$ -- $10^4$ cm$^{-3}$ can be explained by stellar FUV photons.

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