漫射X射线在驱动分子云的光电离中是否重要？
Can diffuse X-rays be important in driving photoionisation in molecular clouds?
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中文总结 AI 辅助
本研究量化了漫射X射线对分子云电离的贡献，发现其在低柱密度下的电离率低于银河宇宙射线，无法主导屏蔽良好的分子气体的电离平衡，仅对低消光物质的热化学结构有一定贡献。
中文摘要 AI 辅助
分子云的电离平衡受多种电离源调控，包括宇宙射线、X射线和紫外线辐射，它们的相对重要性取决于局地物理条件和屏蔽柱密度。在缺乏年轻恒星等强局地X射线源的情况下，我们计算了大尺度漫射X射线辐射场对分子云电离的贡献，目标是量化其相对于银河系宇宙射线的重要性。利用首个eROSITA全天巡天的漫射X射线发射测量结果，我们估算了不同银环境下分子云中随深度变化的X射线电离率，同时考虑了观测到的漫射场和通过逐像素框架利用HI4PI视线柱密度校正前景银河消光得到的消光后漫射场。对于屏蔽良好的分子气体（N_H > 5×10²¹ cm⁻²），漫射银河X射线不太可能主导电离平衡，宇宙射线仍是主要电离剂；在低柱密度下，消光后漫射X射线场在N_H ~ 10¹⁹ cm⁻²处产生的电离率ζ_X ~ 10⁻¹⁸ s⁻¹，仍低于银河系宇宙射线电离率的下限（~10⁻¹⁷ s⁻¹），且X射线贡献随屏蔽增强迅速下降，在N_H ~ 10²¹ cm⁻²处降至ζ_X ~ 10⁻¹⁹ s⁻¹，在N_H ~ 10²² cm⁻²处降至ζ_X ~5×10⁻²¹ s⁻¹。因此，漫射X射线可能对低消光物质的热结构和化学结构有贡献，在解释漫射或云包层环境中的电离示踪剂时应将其纳入考虑。
英文摘要
The ionisation balance in molecular clouds is regulated by several ionising sources, including cosmic rays, X-rays, and ultraviolet radiation. Their relative importance depends on the local physical conditions and on the shielding column density. We compute the contribution of the large-scale diffuse X-ray radiation field to the ionisation in molecular clouds in the absence of strong local X-ray sources, such as young stars. Our goal is to quantify its significance relative to the Galactic cosmic rays. Using measurements of diffuse X-ray emission from the first eROSITA all-sky survey, we estimate the depth-dependent X-ray ionisation rate in molecular clouds across different Galactic environments. We consider both the observed diffuse field and a deabsorbed field obtained by correcting for foreground Galactic attenuation using HI4PI line-of-sight column densities in a pixel-by-pixel framework. Diffuse Galactic X-rays are unlikely to dominate the ionisation balance in well-shielded molecular gas ($N_{\mathrm{H}} > 5 \times 10^{21} \mathrm{cm^{-2}}$), where cosmic rays remain the primary ionising agent. At low column densities, the deabsorbed diffuse X-ray field produces ionisation rate of $ζ_X \sim 10^{-18}\mathrm{s^{-1}}$ at $N_{\mathrm H} \sim 10^{19}\mathrm{cm^{-2}}$, remaining below the lower end of Galactic cosmic ray ionisation rate ($\sim 10^{-17} \mathrm{s^{-1}}$). The X-ray contribution decreases rapidly with increasing shielding, falling to $ζ_{X}\sim10^{-19}\mathrm{s^{-1}}$ by $N_{\rm H}\sim10^{21}\mathrm{cm^{-2}}$ and to $ζ_X \sim5\times10^{-21}\mathrm{s^{-1}}$ by $N_{\rm H}\sim10^{22}\mathrm{cm^{-2}}$. Diffuse X-ray may therefore contribute to the thermal and chemical structure of low-extinction material and should be considered when interpreting ionisation tracers in diffuse or cloud-envelope environments.
发表机构
- Max Planck Institute for Extraterrestrial Physics（马克斯·普朗克地外物理研究所）
- Physics Department, Technion - Israel Institute of Technology（以色列理工学院物理系）
- Faculty of Physics, University of Duisburg-Essen（杜伊斯堡-埃森大学物理学院）
- INAF–Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切特里天文台）
机构由 AI 辅助整理，请以论文原文为准。
