Exploring the magnetized cosmic web through low frequency radio emission

TL;DR

This paper models radio emission from shock waves in the cosmic web to understand magnetic fields and plasma properties, predicting that upcoming radio telescopes can significantly enhance our observational insights.

Contribution

It introduces a simulation-based framework linking radio relics to shock properties and magnetic fields, aiding interpretation of low frequency radio observations of the cosmic web.

Findings

Radio relics trace structure formation shocks and magnetic fields.

Shock Mach numbers can be measured from radio surface brightness peaks.

Future telescopes will significantly increase relic detections and constrain plasma parameters.

Abstract

Recent improvements in the capabilities of low frequency radio telescopes provide a unique opportunity to study thermal and non-thermal properties of the cosmic web. We argue that the diffuse, polarized emission from giant radio relics traces structure formation shock waves and illuminates the large-scale magnetic field. To show this, we model the population of shock-accelerated relativistic electrons in high-resolution cosmological simulations of galaxy clusters and calculate the resulting radio synchrotron emission. We find that individual shock waves correspond to localized peaks in the radio surface brightness map which enables us to measure Mach numbers for these shocks. We show that the luminosities and number counts of the relics strongly depend on the magnetic field properties, the cluster mass and dynamical state. By suitably combining different cluster data, including Faraday rotation measures, we are able to constrain some macroscopic parameters of the plasma at the structure formation shocks, such as models of turbulence. We also predict upper limits for the properties of the warm-hot intergalactic medium, such as its temperature and density. We predict that the current generation of radio telescopes (LOFAR, GMRT, MWA, LWA) have the potential to discover a substantially larger sample of radio relics, with multiple relics expected for each violently merging cluster. Future experiments (SKA) should enable us to further probe the macroscopic parameters of plasma physics in clusters.