论文标题
Ly-Alpha辐射转移：Wouthuysen-Field效应的蒙特卡罗模拟
Ly-alpha Radiative Transfer: Monte-Carlo Simulation of the Wouthuysen-Field Effect
论文作者
论文摘要
开发了一个名为LART的三维蒙特卡洛级辐射转移（RT）代码，以研究Ly-Alpha RT和Wouthuysen-Field（WF）效应。使用代码，我们计算多相星际介质（ISM）内Ly-Alpha辐射的线轮廓，并特别强调低密度下的气体。我们表明，WF效应是在行动的：线轮廓的中央部分倾向于接近一小部分的Planck功能，其色温等于气体的动力温度，即使在具有tau_0〜100-500的光学厚度的系统中也是如此。我们还研究了ISM湍流运动对出现的Ly-Alpha光谱和色温的影响。正如通常预期的那样，湍流运动扩大了新兴光谱，但色温不受典型的天体物理环境中湍流运动的影响。我们利用适合太阳附近的两个多相ISM模型来计算中性氢的21厘米自旋温度，包括通过Ly-Alpha谐振散射激发。第一个ISM模型是一个简单的块状模型，而第二个是使用老虎框架的自一致的磁流失动力学模拟模型。考虑到源自H II区域和碰撞冷却气体的Ly-Alpha光子。我们发现，通常，Ly-Alpha辐射场可能足够强大，可以使温暖的中性培养基的21厘米自旋温度接近动力学温度。在我们的ISM模型中，Ly-Alpha的逃逸部分估计为约7-20％。
A three-dimensional Monte Carlo Ly-alpha radiative transfer (RT) code, named LaRT, is developed to study the Ly-alpha RT and the Wouthuysen-Field (WF) effect. Using the code, we calculate the line profile of Ly-alpha 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 tau_0~100-500. We also investigate the effects of the turbulent motion of the ISM on the emergent Ly-alpha spectrum and color temperature. The turbulent motion broadens, as generally expected, the emergent spectrum, but the color temperature is not affected by the turbulent motion in typical astrophysical environments. We utilize two multiphase ISM models, appropriate for the vicinity of the Sun, to calculate the 21-cm spin temperature of neutral hydrogen, including excitation via the Ly-alpha resonant scattering. The first ISM model is a simple clumpy model, while the second is a self-consistent magnetohydrodynamics simulation model using the TIGRESS framework. Ly-alpha photons originating from both H II regions and the collisionally cooling gas are taken into account. We find that the Ly-alpha radiation field is, in general, likely to be strong enough to bring the 21-cm spin temperature of the warm neutral medium close to the kinetic temperature. The escape fraction of Ly-alpha in our ISM models is estimated to be ~7-20%.
