A formation mechanism for "Wrong Way" Radio Relics

Abstract

Radio Relics are typically found to be arc-like regions of synchrotron emission in the outskirts of merging galaxy clusters, bowing out from the cluster center. In most cases they show synchrotron spectra that steepen towards the cluster center, indicating that they are caused by relativistic electrons being accelerated at outwards traveling merger shocks. A number of radio relics break with this ideal picture and show morphologies that are bent the opposite way and show spectral index distributions which do not follow expectations from the ideal picture. We propose that these `Wrong Way' Relics can form when an outwards travelling shock wave is bent inwards by an in-falling galaxy cluster or group. We test this in an ultra-high resolution zoom-in simulation of a massive galaxy cluster with an on-the-fly spectral Cosmic Ray model. This allows us to study not only the synchrotron emission at colliding shocks, but also their synchrotron spectra to adress the open question of relics with strongly varying spectral indices over the relic surface.

13 pages, 7 figures, accepted for publication in ApJL. arXiv admin note: text overlap with arXiv:2308.00448

References in corpus (28)

• Smoothed Particle Hydrodynamics and Magnetohydrodynamics
• Diffuse Radio Emission from Galaxy Clusters
• Particle Acceleration on Megaparsec Scales in a Merging Galaxy Cluster
• Simultaneous Acceleration of Protons and Electrons at Nonrelativistic Quasiparallel Collisionless Shocks
• Simulating cosmic rays in clusters of galaxies - II. A unified scheme for radio halos and relics with predictions of the gamma-ray emission
• Non-Thermal Electron Acceleration in Low Mach Number Collisionless Shocks. I. Particle Energy Spectra and Acceleration Mechanism
• Simulating cosmic rays in clusters of galaxies - I. Effects on the Sunyaev-Zel'dovich effect and the X-ray emission
• Diffuse radio emission from clusters in the MareNostrum Universe simulation
• The Planck clusters in the LOFAR sky. I. LoTSS-DR2: new detections and sample overview
• An implementation of radiative transfer in the cosmological simulation code GADGET
• Simulating cosmic rays in clusters of galaxies - III. Non-thermal scaling relations and comparison to observations
• Deep LOFAR observations of the merging galaxy cluster CIZA J2242.8+5301
• Testing cosmic-ray acceleration with radio relics: a high-resolution study using MHD and tracers
• Wideband VLA Observations of Abell 2256 I: Continuum, Rotation Measure and Spectral Imaging
• Electron Preacceleration in Weak Quasi-perpendicular Shocks in High-beta Intracluster Medium
• The radio relic in Abell 2256: overall spectrum and implications for electron acceleration
• PIC Simulation Methods for Cosmic Radiation and Plasma Instabilities
• Radio fossils, relics, and haloes in Abell 3266: cluster archaeology with ASKAP-EMU and the ATCA
• Theory of Electron Injection at Oblique Shock of Finite Thickness
• Shock waves in the magnetized cosmic web: the role of obliquity and cosmic-ray acceleration
• Electron Acceleration at Rippled Low-Mach-number Shocks in High-beta Collisionless Cosmic Plasmas
• Radio relics radio emission from multi-shock scenario
• Discovery of a radio halo (and relic) in a $M_{500}<2\times 10^{14}$ M${}_{\odot }$ cluster
• Collision of Merger and Accretion Shocks: Formation of Mpc-scale Contact Discontinuity in the Perseus Cluster
• Chandra and XMM-Newton observations of A2256: cold fronts, merger shocks, and constraint on the IC emission
• MC^2: A deeper look at ZwCl 2341.1+0000 with Bayesian galaxy clustering and weak lensing analyses
• On the Challenges of Cosmic-Ray Proton Shock Acceleration in the Intracluster Medium
• A morphological analysis of the substructures in radio relics