Extended diffuse radio emission in galaxy clusters

Abstract

Galaxy clusters are the most massive gravitationally bound systems in the universe which grow through mergers with other clusters, galaxy groups, and accretion of gas. The mergers generate shocks and turbulence in the intra-cluster medium (ICM). Along the shock edges, particles are accelerated to relativistic energies through multiple crossings at the shock front. The extended diffuse emission sources formed as a result are commonly classified as radio halos and radio relics. The precise nature and origin of the relativistic particles is nevertheless not well understood. We study the nature of the radio relic candidate in Abell 115. We obtain it s spectral properties using radio continuum observations at 150\\,MHz with LOFAR, 610\\,MHz with the GMRT, and 1.5\\,GHz with the VLA. We confirm it s nature as a radio relic. Polarization analyses suggest that part of the large scale synchrotron source is embedded in a region of high ICM density. We show that the galaxy cluster A1430 hosts a two-component radio halo using observations at 150\\,MHz with LOFAR. We obtain the spectral index of the radio halo and derive estimates of the radio power at 1.4 GHz. We also show that a part of the radio halo could be produced via turbulence and the rest lies in a region compressed by the merger via adiabatic compression. Using a 100-m single dish radio telescope, we observe the galaxy clusters PSZ1-G108, Abell 746, 0809+39, and Abell 1367. We detected the polarised flux at 4.85 GHz in all the sources that were previously labelled as radio relics. The radio spectra of the integreted emission below 4.85 GHz can be well fitted with a single power law for all the radio relics. Polarisation observations of radio synchrotron sources offer a method of measuring the strength and geometry of the shock front. The observations of the galaxy clusters PSZ1-G108, Abell 746, 0809+39, and Abell 1367 show that radio relics spectral properties are well represented by a single power-law below 5GHz.