论文标题
动荡的耗散，ch $^+$丰度，h $ _2 $线仪和在冷中性介质中的两极分化
Turbulent dissipation, CH$^+$ abundance, H$_2$ line luminosities, and polarization in the cold neutral medium
论文作者
论文摘要
在冷中性培养基中，高平衡温度是由间歇性耗散过程（包括冲击，粘性加热和双极扩散）创建的。高温偏移被认为可以解释沿弥漫性分子视线观察到的Ch $^{+} $增强的丰度。间歇性的高温也应对h $ _2 $线的发光度产生影响。我们在包括加热和冷却在内的分子云中进行了MHD湍流的模拟，并后处理它们以研究H $ _2 $线排放和热气化学，尤其是CH $^+$的形成。我们探索多个磁场强度和状态方程。我们使用新的H $ _2 $冷却功能，以适用于$ n _ {\ rm h} \ leq 10^5 \，{\ rm cm}^{ - 3} $，$ t \ leq 5000 \，{\ rm k k} $，以及可变的H $ _2 $ frations。我们做出了两个重要的简化假设：（i）$ {\ rm h} _2/{\ rm h} $分数到处固定，并且（ii）我们从分析区域中排除了离子中性漂移速度，该区域被计算为大于5 km/s。我们的模型与许多观察结果一致产生h $ _2 $排放线，尽管某些云中需要额外的激发机制。对于现实的R.M.S.磁场强度（$ \ $ \ 10 $ $ $ g）和速度分散体，我们复制观察到的ch $^+$丰度。这些发现与Valdivia等人的发现形成对比。 （2017）。比较{\ it planck}的预测尘埃极化与观察结果表明，平均场$ \ gtrsim5μ$ g，因此湍流是亚alfvénic。我们建议将来的工作将离子和中性作为单独的流体处理，以更准确地捕获双极扩散对Ch $^+$丰度的影响。
In the cold neutral medium, high out-of-equilibrium temperatures are created by intermittent dissipation processes, including shocks, viscous heating, and ambipolar diffusion. The high-temperature excursions are thought to explain the enhanced abundance of CH$^{+}$ observed along diffuse molecular sight-lines. Intermittent high temperatures should also have an impact on H$_2$ line luminosities. We carry out simulations of MHD turbulence in molecular clouds including heating and cooling, and post-process them to study H$_2$ line emission and hot-gas chemistry, particularly the formation of CH$^+$. We explore multiple magnetic field strengths and equations of state. We use a new H$_2$ cooling function for $n_{\rm H} \leq 10^5\,{\rm cm}^{-3}$, $T\leq 5000\,{\rm K}$, and variable H$_2$ fraction. We make two important simplifying assumptions: (i) the ${\rm H}_2/{\rm H}$ fraction is fixed everywhere, and (ii) we exclude from our analysis regions where the ion-neutral drift velocity is calculated to be greater than 5 km/s. Our models produce H$_2$ emission lines in accord with many observations, although extra excitation mechanisms are required in some clouds. For realistic r.m.s. magnetic field strengths ($\approx 10$ $μ$G) and velocity dispersions, we reproduce observed CH$^+$ abundances. These findings contrast with those of Valdivia et al. (2017). Comparison of predicted dust polarization with observations by {\it Planck} suggests that the mean field $\gtrsim 5 μ$G, so that the turbulence is sub-Alfvénic. We recommend future work treating ions and neutrals as separate fluids to more accurately capture the effects of ambipolar diffusion on CH$^+$ abundance.
