Abstract

We have performed a theoretical calculation of the influence of radiative pumping on the populations of the rotational levels of the ground vibrational state for HD molecules under conditions of the cold phase of the interstellar medium. Two main excitation mechanisms have been taken into account in our analysis: (i) collisions with atoms and molecules of the interstellar medium and (ii) radiative pumping by the ultraviolet interstellar background. The radiative pumping rate coefficients \(\Gamma_{ij}\) corresponding to the average galactic ultraviolet background in Draine’s model have been determined. The influence of HD self-shielding on the radiative pumping rate coefficients has been studied. The population of the first HD rotational level (\(J=1\)) is shown to be determined mainly by radiative pumping rather than by collisions if the thermal gas pressure \(p_{\rm th}\leq 10^{4}\left(\frac{I_{\textrm{UV}}}{1}\right)\textrm{ K cm}^{-3}\) and the column density \(\log N({\textrm{HD}})<15\). In such clouds the relative population of the HD levels \(N(J=1)/N(J=0)\) turns out to be more sensitive to the ultraviolet background intensity than the relative population of the C I fine-structure levels. Thus, an analysis of the relative HD level population can become an important additional source of information about the physical conditions in the interstellar medium both in our Galaxy and in the forming galaxies of the early Universe.

中文翻译：

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辐射泵浦对星际介质弥散分子云中高清旋转能级种群的影响

摘要

我们已经完成了星际介质冷相条件下辐射抽运对HD分子地面振动状态旋转能级总体的影响的理论计算。在我们的分析中考虑了两个主要的激发机制：（i）与星际介质的原子和分子的碰撞，以及（ii）紫外线星际背景的辐射泵浦。确定了与Draine模型中的平均银河紫外线背景相对应的辐射泵浦率系数\（\ Gamma_ {ij} \）。研究了高清自屏蔽对辐射泵浦率系数的影响。第一HD旋转级别（\（J = 1 \））主要由辐射泵浦决定，而不是由热气体压力\（p _ {\ rm th} \ leq 10 ^ {4} \ left（\ frac {I _ {\ textrm {UV}}} { 1} \ right）\ textrm {K cm} ^ {-3} \）和列密度\（\ log N（{\ textrm {HD}}）<15 \）。在这样的云中，HD水平的相对种群\（N（J = 1）/ N（J = 0）\）证明比CI精细结构水平的相对种群对紫外线背景强度更敏感。因此，对相对高清水平种群的分析可能成为有关我们银河系和早期宇宙形成的星系中星际介质中物理条件的重要信息的重要来源。