宇宙学尺度上的协变极化辐射转移研究大尺度磁场结构
Covariant polarized radiative transfer on cosmological scales for investigating large-scale magnetic field structures
摘要：
辐射极化是研究宇宙磁学的有力工具，极化分析可以作为诊断大尺度结构的工具。在本文中，我们提出了一个坚实的理论基础，利用偏振光研究大尺度磁场结构：宇宙学偏振辐射转移（CPRT）制定。CPRT公式是完全协变的。它以自洽的方式解释了宇宙学和相对论效应，并明确地对待法拉第旋转，以及法拉第转换，发射和吸收过程。该公式是从相空间体积守恒和光子数守恒的第一性原理推导出来的。在不失一般性的前提下，我们考虑了平坦的Friedmann-Robertson-Walker（FRW）时空度规，并构造了相应的极化辐射转移方程。我们提出了一个全天空的CPRT计算算法，基于射线跟踪方法，它允许宇宙学模拟结果被纳入，从而，偏振图的模型模板被构造。这些地图对于我们解释偏振数据至关重要，例如平方公里阵列（SKA）收集的数据。我们描述了几个测试，用于验证代码和演示应用程序中的极化签名在不同分布的电子数密度和磁场的研究。我们提出了一个双光束CPRT计算和全天计算，使用一个模拟的星系团或一个模型磁化宇宙从GCMHD+模拟作为各自的输入结构。对大尺度磁场研究的影响进行了讨论，使用旋转测量的标准方法的意见突出。
英文摘要：
Polarization of radiation is a powerful tool to study cosmic magnetism and analysis of polarization can be used as a diagnostic tool for large-scale structures. In this paper, we present a solid theoretical foundation for using polarized light to investigate large-scale magnetic field structures: the cosmological polarized radiative transfer (CPRT) formulation. The CPRT formulation is fully covariant. It accounts for cosmological and relativistic effects in a self-consistent manner and explicitly treats Faraday rotation, as well as Faraday conversion, emission, and absorption processes. The formulation is derived from the first principles of conservation of phase-space volume and photon number. Without loss of generality, we consider a flat Friedmann-Robertson-Walker (FRW) space-time metric and construct the corresponding polarized radiative transfer equations. We propose an all-sky CPRT calculation algorithm, based on a ray-tracing method, which allows cosmological simulation results to be incorporated and, thereby, model templates of polarization maps to be constructed. Such maps will be crucial in our interpretation of polarized data, such as those to be collected by the Square Kilometer Array (SKA). We describe several tests which are used for verifying the code and demonstrate applications in the study of the polarization signatures in different distributions of electron number density and magnetic fields. We present a pencil-beam CPRT calculation and an all-sky calculation, using a simulated galaxy cluster or a model magnetized universe obtained from GCMHD+ simulations as the respective input structures. The implications on large-scale magnetic field studies are discussed; remarks on the standard methods using rotation measure are highlighted.
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