Particle re-acceleration and Faraday-complex structures in the RXC J1314.4-2515 galaxy cluster

TL;DR

This study investigates the magnetic field structures and electron re-acceleration mechanisms in the RXC J1314.4-2515 galaxy cluster's radio relics using multi-frequency radio observations, polarization analysis, and simulations.

Contribution

It provides new insights into the magnetic topology, polarization properties, and shock acceleration efficiency in galaxy cluster relics through combined observational and simulation approaches.

Findings

Detection of polarized emission with 31% polarization fraction at 3 GHz.

Identification of Faraday-complex structures indicating filamentary magnetic fields.

Constraints on the shock Mach number and magnetic field orientation from combined data.

Abstract

Radio relics are sites of electron (re)acceleration in merging galaxy clusters but the mechanism of acceleration and the topology of the magnetic field in and near relics are yet to be understood. We are carrying out an observational campaign on double relic galaxy clusters starting with RXC J1314.4-2515. With $Jansky Very Large Array$ multi-configuration observations in the frequency range 1-4 GHz, we perform both spectral and polarization analyses, using the Rotation Measure synthesis technique. We use archival $XMM-Newton$ observations to constrain the properties of the shocked region. We discover a possible connection between the activity of a radio galaxy and the emission of the eastern radio relic. In the northern elongated arc of the western radio relic, we detect polarized emission with an average polarization fraction of $31 \ \%$ at 3 GHz and we derive the Mach number of the underlying X-ray shock. Our observations reveal low levels of fractional polarization and Faraday-complex structures in the southern region of the relic, which point to the presence of thermal gas and filamentary magnetic field morphology inside the radio emitting volume. We measured largely different Rotation Measure dispersion from the two relics. Finally, we use cosmological magneto-hydrodynamical simulations to constrain the magnetic field, viewing angle, and to derive the acceleration efficiency of the shock. We find that the polarization properties of RXC J1314.4-2515 are consistent with a radio relic observed at $70^{\circ}$ with respect to the line of sight and that efficient re-acceleration of fossil electrons has taken place.