低金属含量环境中致密致密团簇PDR--LMC N159W的亚毫米谱线发射
Submillimeter Line Emission from LMC N159W: a Dense, Clumpy PDR in a Low Metallicity Environment
摘要：
早期宇宙学时期的恒星形成发生在金属丰度较低的星际介质中。大麦云云（LMC）非常适合研究在这样的环境中的恒星形成。ISM在恒星形成环境中的物理和化学状态可以通过观测主要载碳物质CO、CI和CII的亚毫米和远红外谱线来限制，这些物质起源于新形成的年轻恒星的紫外辐射照射的分子云的表面层。本文介绍了利用NANTEN 2望远镜在大麦哲伦星云N159 W区获得的高角分辨率亚毫米观测资料，观测到了12 CO J = 4-3，J = 7-6和1 - 3CO J = 4-3的转动跃迁和[CI] 3 P1 - 3 P0和3 P2 - 3 P1的精细结构跃迁。在LMC中首次检测到~（13）CO J =4-3和[CI]~ 3 P2 - 3 P1跃迁。我们推导出的物理和化学性质的低金属分子气体的逃逸概率代码和自洽的解决方案的化学和热平衡的气体的框架下的clusterium云PDR模型。对亚毫米CO谱线和碳精细结构谱线的单独激发分析表明，N159 W区域的发射气体温度约为80 K，密度约为10^4 cm^-3。估计的C与CO丰度比接近1，远高于银河系中密集的大质量恒星形成区。对所有观测到的谱线进行分析，包括文献中报道的[CII]谱线强度，在云团PDR模型的背景下，将紫外强度限制在约χ~220，云团系综的平均密度约为10^5 cm^-3，从而证实了大麦哲伦星云N159 W区域存在高密度物质。
英文摘要：
Star formation at earlier cosmological times takes place in an interstellar medium with low metallicity. The Large Magellanic Cloud (LMC) is ideally suited to study star formation in such an environment. The physical and chemical state of the ISM in a star forming environment can be constrained by observations of submm and FIR spectral lines of the main carbon carrying species, CO, CI and CII, which originate in the surface layers of molecular clouds illuminated by the UV radiation of the newly formed, young stars. We present high-angular resolution sub-millimeter observations in the N159W region in the LMC obtained with the NANTEN2 telescope of the 12CO J = 4-3, J = 7-6, and 13CO J = 4-3 rotational and [CI] 3P1-3P0 and 3P2-3P1 fine-structure transitions. The 13CO J =4-3 and [CI] 3P2-3P1 transitions are detected for the first time in the LMC. We derive the physical and chemical properties of the low-metallicity molecular gas using an escape probability code and a self-consistent solution of the chemistry and thermal balance of the gas in the framework of a clumpy cloud PDR model. The separate excitation analysis of the submm CO lines and the carbon fine structure lines shows that the emitting gas in the N159W region has temperatures of about 80 K and densities of about 10^4 cm^-3. The estimated C to CO abundance ratio close to unity is substantially higher than in dense massive star-forming regions in the Milky Way. The analysis of all observed lines together, including the [CII] line intensity reported in the literature, in the context of a clumpy cloud PDR model constrains the UV intensity to about χ~220 and an average density of the clump ensemble of about 10^5 cm^-3, thus confirming the presence of high density material in the LMC N159W region.
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