Journal Article

Exploring the magnetized cosmic web through low-frequency radio emission

N. Battaglia, C. Pfrommer, J. L. Sievers, J. R. Bond and T. A. Enßlin

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 393, issue 4, pages 1073-1089
Published in print March 2009 | ISSN: 0035-8711
Published online February 2009 | e-ISSN: 1365-2966 | DOI:
Exploring the magnetized cosmic web through low-frequency radio emission

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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 [Low-Frequency Array (LOFAR), Giant Meter Radio Telescope (GMRT), the Murchison Wide-field Array (MWA) and Long Wavelength Array (LWA)] have the potential to discover a substantially larger sample of radio relics, with multiple relics expected for each violently merging cluster. Future experiments [(Square Kilometre Array (SKA)] should enable us to further probe the macroscopic parameters of plasma physics in clusters.

Keywords: elementary particles; magnetic fields; radiation mechanisms: non-thermal; cosmic rays; galaxies: clusters: general

Journal Article.  11758 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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