Exploring magnetic fields on the largest scales

探索最大尺度的磁场

• 批准号: 2307840
• 负责人: Alexandre Lazarian
• 金额: $ 42.01万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-09-01 至 2026-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2307840&HistoricalAwards=false
• 关键词: Exploring; magnetic; fields; largest; scales

Magnetic fields permeate the cosmos, including in clusters of galaxies where they extend for millions of light years. Recently, magnetic fields were discovered on even larger scales around clusters of galaxies in so-called "megahalos". These magnetic megahalos are important both because their existence challenges theories of the origins of magnetic fields and because they may play a part in the growth of large-scale structure in the universe. Traditional techniques to probe the magnetic field direction fail on these gigantic scales. A team from University of Wisconsin, Madison, have developed a new method, the Gradient Technique (GT), to measure the direction of magnetic fields in megahalos. The GT reveals the magnetic field direction by employing the properties of fluid turbulent motions that are affected by the magnetic field. Maps of magnetic fields obtained using the Chandra X-ray telescope and the LOw Frequency ARray (LOFAR) radio telescope will be used to (1) test theories of the origin of the magnetic field in megahalos, and (2) the part megahalo magnetic fields play in the acceleration of energetic particles and the development of structures within galaxy clusters. Students, both graduate and undergraduates, will be trained in applying the new technique to observational data, analyzing observations and testing theoretical predictions. The team will be actively involved in outreach involving high school students.The team will employ extensive numerical simulations to gauge the accuracy of GT in measuring magnetic fields. Cubes from Galaxy Cluster Merger Catalog will be used for this purpose. The results of the numerical simulations will be used to better understand the effect of key parameters on maps of the magnetic field derived from the GT method. These include plasma magnetization, turbulent Alfven number, the evolutional stage of the cluster and the resolution of the telescope. The GT magnetic maps of the parts of clusters where polarization measurements are possible, i.e., radio relics, will be compared with the available polarization data. The structure of magnetic fields in halos and relics will be compared for merging and relaxed clusters to evaluate the effect of cluster merger. The magnetic structure of clusters with different redshifts, dynamical states, with/without cool cores will be analyzed with the results compared to the theoretical predictions of turbulent dynamo theory. The effects of cosmic ray re-acceleration and propagation will be re-evaluated in view of the obtained magnetic field structure. The predictions of the heat-buoyancy instability in cool cores and magnetothermal instability in outskirts of the galaxy clusters will be compared with the obtained magnetic field data.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

磁场遍布宇宙，包括延伸数百万光年的星系团。 最近，在所谓的“巨晕”星系团周围发现了更大尺度的磁场。这些磁巨晕很重要，因为它们的存在挑战了磁场起源的理论，而且因为它们可能在宇宙中大规模结构的生长中发挥了作用。探测磁场方向的传统技术在如此巨大的尺度上失败了。 威斯康星大学麦迪逊分校的一个团队开发了一种新方法，即梯度技术（GT），用于测量巨晕中的磁场方向。 GT 通过利用受磁场影响的流体湍流运动的特性来揭示磁场方向。使用钱德拉X射线望远镜和低频阵列（LOFAR）射电望远镜获得的磁场图将用于（1）测试巨晕磁场起源的理论，以及（2）巨晕磁场在高能粒子加速和星系团内结构发展中所起的作用。研究生和本科生将接受培训，将新技术应用于观测数据、分析观测结果和测试理论预测。该团队将积极参与涉及高中生的推广活动。该团队将采用广泛的数值模拟来衡量 GT 在测量磁场方面的准确性。星系团合并目录中的立方体将用于此目的。数值模拟的结果将用于更好地理解关键参数对 GT 方法得出的磁场图的影响。其中包括等离子体磁化强度、湍流阿尔文数、星团的演化阶段和望远镜的分辨率。 可以进行极化测量的星团部分（即射电遗迹）的 GT 磁图将与可用的极化数据进行比较。将比较合并和松弛星团的晕和遗迹中的磁场结构，以评估星团合并的效果。将分析具有不同红移、动态状态、有/无冷核的团簇的磁结构，并将结果与​​湍流发电机理论的理论预测进行比较。根据所获得的磁场结构，将重新评估宇宙线再加速和传播的影响。对冷核心的热浮力不稳定性和星系团外围的磁热不稳定性的预测将与获得的磁场数据进行比较。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。