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首页> 外文期刊>The Astrophysical journal >The Atomic-to-molecular Transition In Galaxies. I. An Analytic Approximation For Photodissociation Fronts In Finite Clouds
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The Atomic-to-molecular Transition In Galaxies. I. An Analytic Approximation For Photodissociation Fronts In Finite Clouds

机译：星系中的原子到分子的跃迁。 I.有限云中光解离前沿的解析近似

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In this series of papers, we study the structure of the atomic-to-molecular transition in the giant atomic-molecular complexes that are the repositories of most molecular gas in galaxies, with the ultimate goal of attaining a better understanding of what determines galaxies' molecular content. Here we derive an approximate analytic solution for the structure of a photodissociation region (PDR) in a cloud of finite size that is bathed in an external dissociating radiation field. Our solution extends previous work, which with few exceptions has been restricted to a one-dimensional treatment of the radiation field. We show that our analytic results compare favorably to exact numerical calculations in the one-dimensional limit. However, our more general geometry provides a more realistic representation than a semi-infinite slab for atomic-molecular complexes exposed to the interstellar radiation field, particularly in environments such as low-metallicity dwarf galaxies, where the curvature and finite size of the atomic envelope cannot be neglected. For clouds that are at least 20% molecular, we obtain analytic expressions for the molecular fraction in terms of properties of the gas and radiation field that are accurate to tens of percent, while for clouds of lower molecular content we obtain upper limits. As a side benefit, our analysis helps to clarify when self-shielding is the dominant process in H_2 formation, and under what circumstances shielding by dust makes a significant contribution.
机译：在这一系列论文中，我们研究了巨大的原子分子复合物中的原子到分子的跃迁结构，这些复合物是星系中大多数分子气体的储存库，其最终目标是更好地了解决定银河系的因素。分子含量。在这里，我们得出了沐浴在外部解离辐射场中的有限大小云中光解离区（PDR）结构的近似解析解。我们的解决方案扩展了以前的工作，除少数例外，这些工作仅限于对辐射场进行一维处理。我们表明，我们的分析结果与在一维范围内的精确数值计算相比具有优势。但是，对于暴露于星际辐射场的原子-分子配合物，我们的半球形几何形状比半无限平板更为真实，特别是在诸如低金属矮化星系等环境中，其中原子包络的曲率和有限尺寸不容忽视。对于分子至少为20％的云，我们获得了分子分数的解析表达式，其中气体和辐射场的特性精确到百分之几十，而对于分子含量较低的云，我们获得了上限。作为附带好处，我们的分析有助于弄清何时自我屏蔽是H_2形成过程中的主要过程，以及在什么情况下通过粉尘进行屏蔽会起到重要作用。

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