A three-dimensional Monte Carlo Ly α radiative transfer (RT) code, named LaRT, is developed to study the Ly α RT and the Wouthuysen–Field (WF) effect. Using the code, we calculate the line profile of Ly α radiation within the multiphase interstellar medium (ISM), with a particular emphasis on gas at low densities. We show that the WF effect is in action: the central portion of the line profile tends to approach a small slice of the Planck function with a color temperature equal to the kinetic temperature of the gas, even in a system with an optical thickness as low as τ 0 ≈ 100–500. We also investigate the effects of the turbulent motion of the ISM on the emergent Ly α spectrum and color temperature. The turbulent motion broadens the emergent spectrum, as generally expected, but the color temperature is not affected by the turbulent motion in typical astrophysical environments. We utilize two multiphase ISM models, appropriate for the vi...

中文翻译：

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Lyα辐射传递：Wouthuysen场效应的蒙特卡罗模拟

开发了一个名为LaRT的三维蒙特卡洛Lyα辐射转移（RT）码，以研究LyαRT和Wouthuysen–Field（WF）效应。使用该代码，我们可以计算出多相星际介质（ISM）中Lyα辐射的线形，特别着重于低密度气体。我们证明了WF效应正在起作用：即使在光学厚度低的系统中，线轮廓的中心部分也趋于接近普朗克函数的一小部分，色温等于气体的动力学温度。如τ0≈100–500。我们还研究了ISM湍流对新兴的Lyα光谱和色温的影响。正如人们普遍预期的那样，湍流扩大了出射谱，但在典型的天体物理环境中，色温不受湍流运动的影响。我们利用两个多相ISM模型，适用于可视化应用。