Discovery of a radio relic in the low mass, merging galaxy cluster PLCK G200.9-28.2

Abstract

Radio relics at the peripheries of galaxy clusters are tracers of the elusive cluster merger shocks. We report the discovery of a single radio relic in the galaxy cluster PLCK G200.9-28.2 ($z=0.22$, $M_{500}=2.7\pm 0.2\times 10^{14}{M}_{\odot }$) using the Giant Metrewave Radio Telescope at 235 and 610 MHz and the Karl G. Jansky Very Large Array at 1500 MHz. The relic has a size of $\sim 1\times 0.28$ Mpc, an arc-like morphology and is located at 0.9 Mpc from the X-ray brightness peak in the cluster. The integrated spectral index of the relic is $1.21\pm 0.15$. The spectral index map between 235 and 610 MHz shows steepening from the outer to the inner edge of the relic in line with the expectation from a cluster merger shock. Under the assumption of diffusive shock acceleration, the radio spectral index implies a Mach number of $3.3\pm 1.8$ for the shock. The analysis of archival XMM Newton data shows that PLCK G200.9-28.2 consists of a northern brighter sub-cluster, and a southern sub-cluster in a state of merger. This cluster has the lowest mass among the clusters hosting single radio relics. The position of the Planck Sunyaev Ze'ldovich effect in this cluster is offset by 700 kpc from the X-ray peak in the direction of the radio relic, suggests a physical origin for the offset. Such large offsets in low mass clusters can be a useful tool to select disturbed clusters and to study the state of merger.

10 pages, 7 figures, 4 tables. Accepted for publication in MNRAS

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• Diffuse Radio Emission from Galaxy Clusters
• The MeerKAT Galaxy Cluster Legacy Survey I. Survey Overview and Highlights
• Electron Heating in Low Mach Number Perpendicular shocks. I. Heating Mechanism
• MERGHERS Pilot: MeerKAT discovery of diffuse emission in nine massive Sunyaev-Zel'dovich-selected galaxy clusters from ACT
• The unusually weak and exceptionally steep radio relic in Abell 2108
• SoUthern Cluster sCale Extended Source Survey (SUCCESS): A GMRT and MeerKAT study of nine massive galaxy clusters
• Using the polarization properties of double radio relics to probe the turbulent compression scenario
• Exploring diffuse radio emission in galaxy clusters and groups with the uGMRT and the SKA
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• MeerKAT's discovery of a radio relic in the bimodal merging cluster A2384
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• Radio-relic and the diffuse emission trail discovered in a low mass galaxy cluster Abell 1697
• MOSS I: Double radio relics in the Saraswati supercluster