Cooling and heating functions of cosmic gas are a crucial ingredient for any study of gas dynamics and thermodynamics in the interstellar and intergalactic medium. As such, they have been studied extensively in the past under the assumption of collisional ionization equilibrium. However, for a wide range of applications, the local radiation field introduces a non-negligible, often dominant, modification to the cooling and heating functions. In the most general case, these modifications cannot be described in simple terms, and would require a detailed calculation with a large set of chemical species using a radiative transfer code (the well-known code Cloudy, for example). We show, however, that for a sufficiently general variation in the spectral shape and intensity of the incident radiation field, the cooling and heating functions can be approximated as depending only on several photoionization rates, which can be thought of as representative samples of the overall radiation field. This dependence is easy to tabulate and implement in cosmological or galactic-scale simulations, thus economically accounting for an important but rarely-included factor in the evolution of cosmic gas. We also show a few examples where the radiation environment has a large effect, the most spectacular of which is a quasar that suppresses gas cooling in its host halo without any mechanical or non-radiative thermal feedback.
Can Cooling and Heating Functions be Modeled with Homogeneous Radiation Fields?
Cooling and heating functions describe how radiative processes impact the thermal state of a gas as a function of its temperature and other physical properties. In a most general case the functions depend on the detailed distributions of ionic species and on the radiation spectrum. Hence, these functions may vary on a very wide range of spatial and temporal scales. In this paper, we explore cooling and heating functions between $5\leq z \leq10$ in simulated galaxies from the Cosmic Reionization On Computers (CROC) project. We compare three functions. First, the actual cooling and heating rates…
Cosmic ray heating of intergalactic medium: patchy or uniform?
研究了高红移恒星形成星系周围的星系际介质（IGM）由于宇宙线（CR）的加热。我们考虑到低能量宇宙射线的扩散，并研究由此产生的加热的斑块。我们讨论了高红移微晕（$z\sim 10\hbox{--}20$，M $\sim 10^5\hbox{--}10^7$ M $_\odot$）周围IGM加热的情况，并对扩散系数$D\le 1\times 10^{26}$ cm $^2$ s $^{-1}$设定了上限，以使$z\sim 10$处的加热不均匀，并且$D\le 5\hbox{--}6 \times 10^{26}$ cm $^2$ s $^{-1}$在$z\sim 20$。对于$D$的典型值，我们的结果表明均匀加热CR在高红移，虽然有磁场和其他CR参数的不确定性。我们还讨论了连续恒星形成的两种情况，一种是星系的恒星形成率（SFR）高到足以使附近的IGM光电离，另一种是SFR低到足以保持中性，但高到足以引起宇宙射线质子显着加热。在中性的情况下（低SFR），我们发现，由此产生的加热可以使气体热比宇宙微波背景（CMB）辐射的$D < 10^{30}$厘米$^2$的$^{-1}$，在几千秒差距的星系，不太可能探测到不久的将来的射电观测。在光电离IGM（高SFR）的情况下，在高红移（PDMATHAMBMX）星系附近的气体加热质量$\ge 10^{12}$ M $_\odot$可以抑制气体进入星系。…
