分子云的Cosmic-ray电离
Cosmic-ray ionization of molecular clouds
摘要：
低能宇宙射线是分子云电离的基本来源，影响其化学、热和动力学演化。这项工作的目的是探索宇宙射线的低能量成分的可能性，从地球上不能直接测量，可以解释在弥漫和密集的星际云测量的电离率之间的差异。我们收集了最新的实验和理论数据的横截面的生产H2+和He+的电子和质子的影响，我们讨论了现有的约束条件的宇宙射线通量在本地星际介质。从解调的宇宙线质子和电子谱的低能不同外推出发，考虑到所有相关的能量损失过程，在连续慢化近似下计算了分子云中的传播谱。只有当宇宙射线电子或质子的通量在低能量下增加时，宇宙射线电离率的理论值作为穿过物质的柱密度的函数才与观测数据一致。最成功的模型的特点是一个显着的（甚至占主导地位的）贡献的电子成分的电离速率，与以前的建议。然而，从分子云核的化学模型中推断出的宇宙射线电离率的大范围传播仍有待解释。现有的数据与简单的传播模型相结合，支持宇宙射线电子或质子的低能成分（低于约100兆电子伏）的存在，负责电离的分子云核心和致密的原恒星信封。
英文摘要：
Low-energy cosmic rays are a fundamental source of ionization for molecular clouds, influencing their chemical, thermal and dynamical evolution. The purpose of this work is to explore the possibility that a low-energy component of cosmic-rays, not directly measurable from the Earth, can account for the discrepancy between the ionization rate measured in diffuse and dense interstellar clouds. We collect the most recent experimental and theoretical data on the cross sections for the production of H2+ and He+ by electron and proton impact, and we discuss the available constraints on the cosmic-ray fluxes in the local interstellar medium. Starting from different extrapolations at low energies of the demodulated cosmic-ray proton and electron spectra, we compute the propagated spectra in molecular clouds in the continuous slowing-down approximation taking into account all the relevant energy loss processes. The theoretical value of the cosmic-ray ionization rate as a function of the column density of traversed matter is in agreement with the observational data only if either the flux of cosmic-ray electrons or of protons increases at low energies. The most successful models are characterized by a significant (or even dominant) contribution of the electron component to the ionization rate, in agreement with previous suggestions. However, the large spread of cosmic-ray ionization rates inferred from chemical models of molecular cloud cores remains to be explained. Available data combined with simple propagation models support the existence of a low-energy component (below about 100 MeV) of cosmic-ray electrons or protons responsible for the ionization of molecular cloud cores and dense protostellar envelopes.
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