Infrared Response of H2 to X-Rays in Dense Clouds
Infrared Response of H2 to X-Rays in Dense Clouds
复制标题
浓云中 H2 对 X 射线的红外响应
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
A. Dalgarno
中科院分区：
文献类型：
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作者：
S. Tiné;S. Lepp;R. Gredel;A. Dalgarno
分析了X射线和宇宙射线对星际云中氢分子的激发。我们进行了详细的计算，在振转水平的H2与快速电子产生的X射线电离的气体的影响后的入口效率。详细研究了碰撞激发和淬火的竞争效应。采用了H-H_2碰撞速率系数的最新值，并对已有文献中的H_2-H_2振转速率系数进行了推导。几个模型作为温度，密度和电离率的函数。我们发现，在X射线主导区（XDR）的H2红外发射是潜在的可观察的温度和电离率低于某些临界值（通常T < 1000 K和nH/nH < 10-15 cm 3 s-1，其中nH是电离率）。在较高的温度下，碰撞激发的环境气体占主导地位的人口低振动水平，并在较高的值的H2/nH的丰度是可以忽略不计的。如果满足这些条件，所产生的红外发射光谱可以用作附近X射线源的诊断，例如星系团、类星体、塞弗特星系和超新星遗迹中的冷却流。在塞弗特星系NGC 1275中测量到的2- 1 S（1）和1- 0 S（1）线的强度比与X射线泵浦一致。
The excitation by X-rays and cosmic rays of molecular hydrogen in interstellar clouds is analyzed. We carried out detailed calculations of entry efficiencies in rovibrational levels of H2 following impact with fast electrons produced by X-ray ionization of the gas. The competing effect of collisional excitation, and quenching, by the ambient gas is examined in detail. Up to date values for H-H2 collisional rate coefficients are adopted, and some derivations of H2-H2 rovibrational rate coefficients from existing literature data are proposed. Several models as a function of temperature, density, and ionization rate are presented. We found that H2 infrared emission in X-ray dominated regions (XDR) is potentially observable for temperatures and ionization rates lower than certain critical values (typically T < 1000 K and ζ/nH < 10-15 cm3 s-1, where ζ is the ionization rate). At higher temperatures, collisional excitation by the ambient gas dominates the population of low vibrational levels, and at higher values of ζ/nH the abundance of H2 is negligible. If such conditions are satisfied, the resulting infrared emission spectrum can be used as a diagnostic of nearby X-ray sources such as in cooling flows in galaxy clusters, quasars, Seyfert galaxies and supernova remnants. The intensity ratio of the 2-1S(1) and 1-0S(1) lines measured for the Seyfert galaxy NGC 1275 is consistent with X-ray pumping.