The wealth of high-quality observational data from the epoch of reionization that will become available in the next decade motivates further development of modeling techniques for their interpretation. Among the key challenges in modeling reionization are (1) its multi-scale nature, (2) the computational demands of solving the radiative transfer (RT) equation, and (3) the large size of reionization's parameter space. In this paper, we present and validate a new RT code designed to confront these challenges. FlexRT (Flexible Radiative Transfer) combines adaptive ray tracing with a highly flexible treatment of the intergalactic ionizing opacity. This gives the user control over how the intergalactic medium (IGM) is modeled, and provides a way to reduce the computational cost of a FlexRT simulation by orders of magnitude while still accounting for small-scale IGM physics. Alternatively, the user may increase the angular and spatial resolution of the algorithm to run a more traditional reionization simulation.FlexRT has already been used in several contexts, including simulations of the Lyman-α forest of high-z quasars, the redshifted 21cm signal from reionization, as well as in higher resolution reionization simulations in smaller volumes. In this work, we motivate and describe the code, and validate it against a set of standard test problems from the Cosmological Radiative Transfer Comparison Project. We find that FlexRT is in broad agreement with a number of existing RT codes in all of these tests. Lastly, we compare FlexRT to an existing adaptive ray tracing code to validate FlexRT in a cosmological reionization simulation.

中文翻译：

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FlexRT — 一种用于再电离研究的快速灵活的宇宙学辐射传输代码。第一部分 代码验证


未来十年将提供的来自再电离时代的大量高质量观测数据，这推动了进一步开发解释它们的建模技术。再电离建模的主要挑战包括 （1） 其多尺度性质，（2） 求解辐射传输 （RT） 方程的计算需求，以及 （3） 再电离参数空间的大尺寸。在本文中，我们提出并验证了一种旨在应对这些挑战的新 RT 代码。FlexRT（Flexible Radiative Transfer）将自适应光线追踪与星际电离不透明性的高度灵活处理相结合。这使用户可以控制星系际介质 （IGM） 的建模方式，并提供一种方法，可以将 FlexRT 仿真的计算成本降低几个数量级，同时仍考虑小规模 IGM 物理。或者，用户可以提高算法的角度和空间分辨率，以运行更传统的再电离仿真。FlexRT 已经用于多种环境，包括高 z 类星体的莱曼α森林模拟、再电离产生的红移 21cm 信号，以及较小体积的更高分辨率再电离模拟。在这项工作中，我们激发和描述代码，并根据宇宙学辐射传输比较项目的一组标准测试问题对其进行验证。我们发现，在所有这些测试中，FlexRT 与许多现有的 RT 代码基本一致。最后，我们将 FlexRT 与现有的自适应光线追踪代码进行比较，以在宇宙学再电离模拟中验证 FlexRT。