辐射驱动沙尘风的数值模拟
Numerical Simulations of Radiatively-Driven Dusty Winds
摘要：
尘埃颗粒上的辐射压力可能是在各种天体物理系统中驱动风的重要机制。然而，辐射场和含尘气体之间的耦合的效率是知之甚少的环境中，其特征在于高的光学深度。我们提出了一系列理想化的数值实验，进行辐射流体动力学代码ORION，在其中我们研究这种风的动力学和量化其属性。我们发现，在风加速开始后，辐射瑞利-泰勒不稳定性迫使气体进入一种配置，与基于大气底部光学厚度的估计相比，该配置将从辐射场到气体的动量传递速率降低了约10 - 100倍;相反，从亮度为L的驱动辐射场到气体的动量传递速率大致为L/c乘以1加上使用光球温度估计的光学深度的一半，其远小于使用内部温度所获得的光学深度。当我们将我们的结果适用于ULIRGs和星团的条件下，我们发现，渐近风动量通量从这样的对象不应该显着超过所携带的直接辐射场，L/C。这一结果限制了预期的质量损失率从系统，超过爱丁顿限制的顺序，所谓的“单散射”的限制，而不是显着更高。我们提出了一个近似的拟合公式的动量转移率从辐射尘埃气体通过它，这是适合于实施的亚网格模型的星系形成。最后，我们提供了第一张地图的柱密度分布的气体在辐射驱动风的速度和速度色散的函数。
英文摘要：
[abridged] Radiation pressure on dust grains may be an important mechanism in driving winds in a wide variety of astrophysical systems. However, the efficiency of the coupling between the radiation field and the dusty gas is poorly understood in environments characterized by high optical depths. We present a series of idealized numerical experiments, performed with the radiation-hydrodynamic code ORION, in which we study the dynamics of such winds and quantify their properties. We find that, after wind acceleration begins, radiation Rayleigh-Taylor instability forces the gas into a configuration that reduces the rate of momentum transfer from the radiation field to the gas by a factor ~ 10 - 100 compared to an estimate based on the optical depth at the base of the atmosphere; instead, the rate of momentum transfer from a driving radiation field of luminosity L to the gas is roughly L/c multiplied by one plus half the optical depth evaluated using the photospheric temperature, which is far smaller than the optical depth one would obtain using the interior temperature. When we apply our results to conditions appropriate to ULIRGs and star clusters, we find that the asymptotic wind momentum flux from such objects should not significantly exceed that carried by the direct radiation field, L/c. This result constrains the expected mass loss rates from systems that exceed the Eddington limit to be of order the so-called "single-scattering" limit, and not significantly higher. We present an approximate fitting formula for the rate of momentum transfer from radiation to dusty gas through which it passes, which is suitable for implementation in sub-grid models of galaxy formation. Finally, we provide a first map of the column density distribution of gas in a radiatively-driven wind as a function of velocity, and velocity dispersion.
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