星系团星系团内介质中法拉第旋转量的宇宙学演化
Cosmic evolution of the Faraday rotation measure in the intracluster medium of galaxy clusters
AI总结：
本研究利用弱碰撞发电机模型模拟了星系团内介质中法拉第旋转量至红移1.5的演化，发现其标准差和绝对平均值随星系团质量增加而增加，且径向剖面与红移无关，模型结果与观测数据吻合，可用于生成射电望远镜的模拟偏振观测。
摘要：
射电观测揭示了星系团内介质（ICM）中的磁场几乎与湍流处于能量均分状态。这表明磁场是通过发电机过程放大的。然而，观测仅限于红移 z <~ 0.7，且 ICM 的弱碰撞特性使得通过理论模型和模拟研究更高红移处的磁场演化变得复杂。使用弱碰撞发电机模型，我们模拟了不同质量星系团中法拉第旋转量（RM）的演化（至 z <~ 1.5），并研究了其性质。我们将结果与各种星系团的射电观测进行了比较。我们使用由改进的 GALFORM 算法生成的并合树来追踪星系团形成过程中等离子体物理量的演化。假设磁场保持与湍流速度场的能量均分，我们生成了 RM 图以研究其性质。我们发现 RM 的标准差 sigma_RM 和绝对平均值 |mu_RM| 均随星系团质量增加而增加。由于红移稀释效应，对于固定质量的星系团，其 RM 值在 z=0 到 z=1.5 之间保持近乎恒定。对于 r/r200 >~ 0.4，sigma_RM 不随 L/r200 显著变化（L 为观测 RM 区域的大小）。低于此界限时，sigma_RM 随 L 减小而增加。我们发现径向 RM 剖面具有一致的形状，与 10^{-1.2(r/r200)} 成正比，且几乎与红移无关。我们针对 M_clust = 10^15 Msol 的 z~0 剖面与后发座星系团的 RM 观测相符，但与英仙座存在差异，这可能归因于高气体混合。对于 M_clust = 10^13 和 M_clust = 10^15 Msol 的星系团，在 z=0 和 z=0.174 处的模型在 r/r200 <~ 0.4 范围内与天炉座和 A2345 的数据高度吻合。我们的模型可用于为射电望远镜生成模拟偏振观测。
英文摘要：
Radio observations have revealed magnetic fields in the intracluster medium (ICM) of galaxy clusters nearly in equipartition with turbulence. This suggests magnetic field amplification by dynamo processes. However, observations are limited to redshifts z <~ 0.7, and the weakly collisional nature of the ICM complicates studying magnetic field evolution at higher redshifts through theoretical models and simulations. Using a model of the weakly collisional dynamo, we modelled the evolution of the Faraday rotation measure (RM) in clusters of different masses, up to z <~ 1.5, and investigated its properties. We compared our results with radio observations of various galaxy clusters. We used merger trees generated by the modified GALFORM algorithm to track the evolution of plasma quantities during galaxy cluster formation. Assuming the magnetic field remains in equipartition with the turbulent velocity field, we generated RM maps to study their properties. We find that both the standard deviation of RM, sigma_RM, and the absolute average |mu_RM| increase with cluster mass. Due to redshift dilution, RM values for a fixed cluster mass remain nearly constant between z=0 and z=1.5. For r/r200 >~ 0.4, sigma_RM does not vary significantly with L/r200, with L being the size of the observed RM patch. Below this limit, sigma_RM increases as L decreases. We find that radial RM profiles have a consistent shape, proportional to 10^{-1.2(r/r200)}, and are nearly independent of redshift. Our z~0 profiles for M_clust = 10^15 Msol match RM observations in the Coma cluster but show discrepancies with Perseus, possibly due to high gas mixing. Models for clusters with M_clust = 10^13 and M_clust = 10^15 Msol at z=0 and z = 0.174 align well with Fornax and A2345 data for r/r200 <~ 0.4. Our model can be useful for generating mock polarization observations for radio telescopes.
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