Non-equilibrium chemistry and cooling in the diffuse interstellar medium – II. Shielded gas
Non-equilibrium chemistry and cooling in the diffuse interstellar medium – II. Shielded gas
复制标题
扩散星际介质中的非平衡化学和冷却 – II。
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
我们扩展了Richings等人（2014）提出的diuse星际气体化学和热演化的非平衡模型。我们衰减的光化学速率的灰尘和气体，包括吸收的Hi，H2，Hei，Heii和CO在适当的情况下。然后，我们使用这个模型来研究星际气体中占主导地位的冷却和加热过程，因为它成为屏蔽紫外线辐射。我们考虑一个一维的平面平行板的气体照射的星际辐射场，无论是在恒定的密度和温度或在热和压力平衡。主要的热过程倾向于在云中形成三个不同的区域。在低柱密度下，冷却由离子化金属如SiII、FeII、FeIII和CII主导，其通过主要来自Hi的光加热来平衡。一旦氢电离辐射被中性氢衰减，光电尘埃加热占主导地位，而Cii则成为冷却的主导。最后，灰尘屏蔽触发CO的形成并抑制光电加热。在这个完全屏蔽的区域中占主导地位的冷却剂是H2和CO。我们的模型预测的Hi-H2过渡的柱密度在较高的密度（或在较高的压力下的气体云压力平衡）和较高的金属丰度下较低，与以前的PDR模型一致。我们还比较了Hi-H2过渡在我们的模型中的两个处方的分子氢的形成，已实施的流体动力学模拟。
We extend the non-equilibrium model for the chemical and thermal evolution of diuse interstellar gas presented in Richings et al. (2014) to account for shielding from the UV radiation eld. We attenuate the photochemical rates by dust and by gas, including absorption by Hi, H2, Hei, Heii and CO where appropriate. We then use this model to investigate the dominant cooling and heating processes in interstellar gas as it becomes shielded from the UV radiation. We consider a one-dimensional plane-parallel slab of gas irradiated by the interstellar radiation eld, either at constant density and temperature or in thermal and pressure equilibrium. The dominant thermal processes tend to form three distinct regions in the clouds. At low column densities cooling is dominated by ionised metals such as Siii, Feii, Feiii and Cii, which are balanced by photoheating, primarily from Hi. Once the hydrogen-ionising radiation becomes attenuated by neutral hydrogen, photoelectric dust heating dominates, while Cii becomes dominant for cooling. Finally, dust shielding triggers the formation of CO and suppresses photoelectric heating. The dominant coolants in this fully shielded region are H2 and CO. The column density of the Hi-H2 transition predicted by our model is lower at higher density (or at higher pressure for gas clouds in pressure equilibrium) and at higher metallicity, in agreement with previous PDR models. We also compare the Hi-H2 transition in our model to two prescriptions for molecular hydrogen formation that have been implemented in hydrodynamic simulations.
DOI：
10.1088/0004-6256/140/5/1194
发表时间：
2010-07
期刊：
The Astronomical Journal
影响因子：
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作者：
F. Bigiel;A. Leroy;F. Walter;L. Blitz;E. Brinks;W. D. Blok;B. M. U. Berkeley;Mpia Heidelberg;Nrao;U. Hertfordshire;U. C. Town;C. Observatories
通讯作者：
F. Bigiel;A. Leroy;F. Walter;L. Blitz;E. Brinks;W. D. Blok;B. M. U. Berkeley;Mpia Heidelberg;Nrao;U. Hertfordshire;U. C. Town;C. Observatories