PRODIGIES: Polarised Radio Observations of DIGItal Extragalactic Shocks

PRODIGIES：数字河外激波的偏振射电观测

• 批准号: 441694982
• 负责人: Professor Dr. Marcus Brüggen, Ph.D., since 1/2023
• 金额: --
• 依托单位: Hamburger Sternwarte
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2020
• 资助国家: 德国
• 起止时间: 2019-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/441694982?language=en
• 关键词: PRODIGIES; Polarised; Radio; Observations; DIGItal

Radio relics belong to the most spectacular sources in the radio sky. These large and mostly elongated sources are found the periphery of galaxy clusters where they emit synchrotron emission, illuminating large-scale magnetic fields and cosmic-ray electrons. Moreover, they are mostly polarised, with average degrees of polarisation up to 60 %. X-ray observations show that radio relics are co-located with shock waves, suggesting that shock waves accelerate electrons from the thermal pool into the relativistic regime. Still, several unsolved questions in the understanding of radio relics exist. Mainly, the origin of the large-scale magnetic fields and the exact particle acceleration mechanism are still unknown. Theoretical studies showed that the acceleration does not only depend on the shock strength but also on the conditions of the local magnetic fields. Hence, proper knowledge of the magnetic fields is needed for the complete understanding of radio relics. The combination of low- and high-frequency radio observations is a perfect tool to derive a three-dimensional picture of the magnetic fields. The observed luminosities are a measurement of the local magnetic field strength. In particular, low-frequency observations, that are sensitive to lower energetic particles, can provide information on the strengths and variations of the downstreammagnetic fields. However, the polarisation signal, that is best measured at high frequencies, gives the orientation of the magnetic field in the plane of the sky. This is complemented by Faraday rotation measurements, that give the strength and direction of the magnetic field along the line-of-sight. Nowadays, several radio telescopes are deployed to study radio relics across all radio wavelengths and cosmological simulations are an essential tool to connect these observations and theory. In order to keep up with the advances in observations, simulations need to model a larger variety of phenomena. In particular, a net advancement in their ability to mimic complex radio emission is presently missing, and this is the motivation for this project proposal. I will use state-of-the-art cosmological simulations of magnetic fields and particle acceleration to model the diffuse emission of radio relics. The main parts of the project are:1) production of a catalogue of simulated radio relics to study the statistical properties and to help to interpret observations2) including re-acceleration to improve the modelling of cosmic-ray electrons 3) using active galaxies as sources of seed electrons4) combining simulations and observations to constrain the cosmic-ray energy budget and the acceleration efficiency5) exposing possible limitations of the observational techniques to study radio relicsHence, I will help to answer two key and unsolved questions in the understanding of radio relics: 1) What are the exact acceleration efficiencies? 2) How do relics obtain their high degree of polarisation?

无线电遗迹属于无线电天空中最壮观的来源。这些巨大且大多拉长的源位于星系团的外围，它们在那里发射同步辐射，照亮大范围的磁场和宇宙射线电子。此外，它们大多是偏振的，平均偏振度高达60%。X射线观测表明，射电遗迹与冲击波位于同一位置，这表明激波将电子从热池加速进入相对论区域。尽管如此，对无线电遗迹的理解仍然存在几个悬而未决的问题。主要的是，大尺度磁场的起源和确切的粒子加速机制仍然未知。理论研究表明，加速度不仅与冲击强度有关，还与局部磁场条件有关。因此，要完全理解无线电遗迹，就需要适当的磁场知识。低频和高频射电观测的结合是得出磁场三维图像的完美工具。观测到的光度是对局部磁场强度的测量。特别是，对低能量粒子敏感的低频观测可以提供关于下行磁场的强度和变化的信息。然而，偏振信号最好在高频下测量，它给出了磁场在天空平面上的方向。这与法拉第旋转测量是相辅相成的，它给出了沿视线的磁场强度和方向。如今，人们部署了几个射电望远镜来研究所有射电波长的射电遗迹，宇宙学模拟是将这些观测与理论联系起来的重要工具。为了跟上观测的进步，模拟需要模拟更多种类的现象。特别是，目前还没有在模拟复杂射电发射能力方面取得净进步，这是本项目提案的动机。我将使用最先进的磁场和粒子加速的宇宙学模拟来模拟射电遗迹的漫射辐射。该项目的主要部分是：1)制作模拟射电遗迹目录，以研究统计性质并帮助解释观测结果2)包括重新加速以改进宇宙线电子的建模3)使用活动星系作为种子电子源4)结合模拟和观测以限制宇宙线能量收支和加速效率5)揭示研究射电遗迹的观测技术可能存在的局限性因此，我将帮助回答在理解射电遗迹方面的两个关键和悬而未决的问题：1)确切的加速效率是什么？2)遗迹如何获得高度的极化？