一个低金属量巨分子云配合物的结构
The Structure of a Low-Metallicity Giant Molecular Cloud Complex
摘要：
为了了解低金属丰度对巨分子云（GMC）结构的影响，我们比较了小麦哲伦云翼中恒星形成复合体N83的远红外尘埃发射，CO发射和动力学。尘埃排放（由斯皮策测量的S3 MC和SAGE-SMC调查的一部分）探测总的气体柱独立的分子线发射和痕迹屏蔽光离解辐射。我们校准的方法来估计尘埃柱仅使用高分辨率的斯皮策数据，并验证尘埃痕迹的ISM在HI占主导地位的区域周围N83。这使我们能够解决一个巨大的分子云复合体中H2，尘埃和CO的相对结构，这是第一次在低金属量星系中进行这样的测量。我们的研究结果支持的假设，CO是光解，而H2的自屏蔽在外部的低金属丰度GMCs，所以灰尘/自屏蔽是决定CO排放的分布的主要因素。有四个证据支持这一观点。首先，整个星云的平均CO到H2的转换因子非常高4-11 \times 10^21 cm^-2/（K km/s），或者说是银河系数值的20-55倍。其次，CO到H2的转换因子在整个复合体中变化，其最低（最接近银河系）值接近CO峰值。第三，明亮的CO辐射主要局限于相对高的视线消光区域，A_V >~ 2等，与PDR模型和银河系观测结果一致。第四，一个简单的模型中，CO出现从一个较小的球体嵌套在一个较大的云可以大致相关的H2质量从CO运动学和尘埃测量。
英文摘要：
To understand the impact of low metallicities on giant molecular cloud (GMC) structure, we compare far infrared dust emission, CO emission, and dynamics in the star-forming complex N83 in the Wing of the Small Magellanic Cloud. Dust emission (measured by Spitzer as part of the S3MC and SAGE-SMC surveys) probes the total gas column independent of molecular line emission and traces shielding from photodissociating radiation. We calibrate a method to estimate the dust column using only the high-resolution Spitzer data and verify that dust traces the ISM in the HI-dominated region around N83. This allows us to resolve the relative structures of H2, dust, and CO within a giant molecular cloud complex, one of the first times such a measurement has been made in a low-metallicity galaxy. Our results support the hypothesis that CO is photodissociated while H2 self-shields in the outer parts of low-metallicity GMCs, so that dust/self shielding is the primary factor determining the distribution of CO emission. Four pieces of evidence support this view. First, the CO-to-H2 conversion factor averaged over the whole cloud is very high 4-11 \times 10^21 cm^-2/(K km/s), or 20-55 times the Galactic value. Second, the CO-to-H2 conversion factor varies across the complex, with its lowest (most nearly Galactic) values near the CO peaks. Third, bright CO emission is largely confined to regions of relatively high line-of-sight extinction, A_V >~ 2 mag, in agreement with PDR models and Galactic observations. Fourth, a simple model in which CO emerges from a smaller sphere nested inside a larger cloud can roughly relate the H2 masses measured from CO kinematics and dust.
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