On the largest scales, the Universe consists of voids and filaments making up the cosmic web. Galaxy clusters are located at the knots in this web, at the intersection of filaments. Clusters grow... Show moreOn the largest scales, the Universe consists of voids and filaments making up the cosmic web. Galaxy clusters are located at the knots in this web, at the intersection of filaments. Clusters grow through accretion from these large-scale filaments and by mergers with other clusters and groups. In a growing number of galaxy clusters, elongated Mpc-sized radio sources have been found1,2 . Also known as radio relics, these regions of diffuse radio emission are thought to trace relativistic electrons in the intracluster plasma accelerated by low-Mach-number shocks generated by cluster–cluster merger events 3 . A long-standing problem is how low-Mach-number shocks can accelerate electrons so efficiently to explain the observed radio relics. Here, we report the discovery of a direct connection between a radio relic and a radio galaxy in the merging galaxy cluster Abell 3411–3412 by combining radio, X-ray and optical observations. This discovery indicates that fossil relativistic electrons from active galactic nuclei are re-accelerated at cluster shocks. It also implies that radio galaxies play an important role in governing the non-thermal component of the intracluster medium in merging clusters. Show less
We present Very Large Array (VLA) radio and Chandra X-ray observations of the merging galaxy cluster A3411. For the cluster, we find an overall temperature of 6.4^{}${$+0.6$}$_${$-1.0$}$ keV and... Show moreWe present Very Large Array (VLA) radio and Chandra X-ray observations of the merging galaxy cluster A3411. For the cluster, we find an overall temperature of 6.4^{}${$+0.6$}$_${$-1.0$}$ keV and an X-ray luminosity of 2.8 {plusmn} 0.1 { imes} 10$^{44}$ erg s$^{-1}$ between 0.5 and 2.0 keV. The Chandra observation reveals the cluster to be undergoing a merger event. The VLA observations show the presence of large-scale diffuse emission in the central region of the cluster, which we classify as a 0.9 Mpc size radio halo. In addition, a complex region of diffuse, polarized emission is found in the southeastern outskirts of the cluster along the projected merger axis of the system. We classify this region of diffuse emission as a radio relic. The total extent of this radio relic is 1.9 Mpc. For the combined emission in the cluster region, we find a radio spectral index of -1.0 {plusmn} 0.1 between 74 MHz and 1.4 GHz. The morphology of the radio relic is peculiar, as the relic is broken up into five fragments. This suggests that the shock responsible for the relic has been broken up due to interaction with a large-scale galaxy filament connected to the cluster or other substructures in the intracluster medium. Alternatively, the complex morphology reflects the presence of electrons in fossil radio bubbles that are re-accelerated by a shock. Show less