Contributed Talk - Splinter Magnetic

Thursday, 24 September 2020, 09:37   (virtual room H)

Unveiling large-scale magnetic fields using radio observations (insights from simulations)

D. Wittor (1); F. Vazza (2); M. Hoeft (3); M. Brüggen (1); K. Rajpurohit (2); C. Stuardi (2)
(1) Universität Hamburg; (2) Università Di Bologna; (3) Thüringer Landessternwarte Tautenburg

In this contribution, I will discuss our on-going systematic numerical investigation of radio relics and large-scale magnetic fields in galaxy clusters. In the periphery of clusters, Megaparsec-size diffuse radio sources, called radio relics, proof the existence of magnetic fields and cosmic-ray electrons on cluster scales. These elongated and highly polarised sources trace shock waves in the intracluster medium and, hence, it is assumed that these shock waves accelerate cosmic-ray electrons. Yet, neither the origin of the cosmological magnetic fields nor the exact acceleration mechanism are known. Therefore, the study of radio relics is of high interest as they probe both the intracluster magnetic fields and the shock acceleration of cosmic-ray electrons on large-scales. Radio telescopes provide the perfect tool to study radio relics: High frequency radio observations enlarge our view on the magnetic field at the shock front, while low frequency observations explore the magnetic fields in the downstream region. In addition, polarisation observations and measurements of the Rotation Measure yield information on the magnetic field orientation and the magnetic field along the line-of-sight, respectively. Hence, radio observations are able to produce a three-dimensional picture of the magnetic fields at the radio relics. This helps to explain the origin of magnetic fields and to pin-point the exact shock acceleration mechanism of cosmic-ray electrons in the intracluster medium. As modern facilities as Lofar, the VLA or the uGMRT produce more and more spectacular images of radio relics, it becomes more and more difficult to interpret these. Hence, cosmological simulations are an inevitable tool to connect observation and theory. In this talk, I will present our latest advances in the numerical modeling of radio relics. These models include, for the first time, the aging of cosmic-ray electrons behind the shock front. Moreover, they are able to reproduce realistic features as observed in real radio relics. This provides new possibilities to study radio relics and, more importantly, the associated large-scale magnetic fields. First, I will give a brief background on the used simulations and underlying theoretical models. Following, I will present the results obtained from a simulated galaxy cluster that hosts a radio relic, which can be considered as the textbook example of a radio relic. I will focus the physical features of the simulated magnetic fields and how they are appear in the radio relic. Finally, I will give examples on how these results have been successful applied to the interpretation of real observations. Specifically, I will show examples for the relics observed in RXC 1314.4-2515 and 1RXS J0603.3+4214.