Non-equilibrium chemistry and cooling in the diffuse interstellar medium – I. Optically thin regime
Non-equilibrium chemistry and cooling in the diffuse interstellar medium – I. Optically thin regime
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弥漫星际介质中的非平衡化学和冷却 – I. 光学薄态
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
B. Oppenheimer
中科院分区：
文献类型：
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作者：
A. J. Richings;J. Schaye;B. Oppenheimer
在流体动力学星系模拟的多相星际介质（ISM）的准确治疗要求我们遵循不仅是气体的热演化，而且其化学状态的演变，包括其分子化学，而不假设化学（包括电离）平衡。我们提出了一个反应网络，可用于解决这种热化学演化。我们的模型如下的11种元素，占主导地位的冷却速率，沿着重要的分子，如H2和CO，以及中间分子物种，参与其形成（共20个分子）的所有电离状态的演变。我们包括尘埃颗粒上的化学反应，涉及尘埃的热过程，宇宙射线电离和加热以及光化学反应。我们关注的是弥漫ISM的典型条件，密度为10^-2 cm^-3 × 10 ^2 cm^-3。最后，我们研究了非平衡化学对等容或等压冷却气体冷却功能的影响。我们发现，在T < 10^4 K时，复合滞后使电子丰度增加到高于给定温度下的平衡值，这可以使冷却速率提高两个数量级。冷却气体也显示出较低的H2丰度比在平衡，由高达一个数量级。
An accurate treatment of the multiphase interstellar medium (ISM) in hydrodynamic galaxy simulations requires that we follow not only the thermal evolution of the gas, but also the evolution of its chemical state, including its molecular chemistry, without assuming chemical (including ionisation) equilibrium. We present a reaction network that can be used to solve for this thermo-chemical evolution. Our model follows the evolution of all ionisation states of the 11 elements that dominate the cooling rate, along with important molecules such as H2 and CO, and the intermediate molecular species that are involved in their formation (20 molecules in total). We include chemical reactions on dust grains, thermal processes involving dust, cosmic ray ionisation and heating and photochemical reactions. We focus on conditions typical for the diffuse ISM, with densities of 10^-2 cm^-3 10^2 cm^-3. Finally, we investigate the impact of non-equilibrium chemistry on the cooling functions of isochorically or isobarically cooling gas. We find that, at T < 10^4 K, recombination lags increase the electron abundance above its equilibrium value at a given temperature, which can enhance the cooling rate by up to two orders of magnitude. The cooling gas also shows lower H2 abundances than in equilibrium, by up to an order of magnitude.