Discovery of a nearby radio relic in the low-mass, merging cluster Abell 4067

TL;DR

This paper reports the discovery of a radio relic in the low-mass galaxy cluster Abell 4067, providing new insights into merger-driven shock waves and diffuse radio emissions in such environments.

Contribution

It presents the first detection of a radio relic in a low-mass cluster, expanding understanding of relic formation in less energetic merger scenarios.

Findings

Relic size is approximately 1.48 Mpc.

Relic's radio power is about 3.10 x 10^{24} W/Hz at 150 MHz.

Relic's properties suggest formation through weak merger shocks.

Abstract

Shock waves generated during cluster mergers offer a powerful probe of how large-scale structure grows and evolves in the Universe. As part of the MeerKAT-South Pole Telescope (SPT) survey, we report the discovery of a single arc-like radio relic in the galaxy cluster Abell 4067 ($z=0.099$), one of the lowest-mass clusters known to host such a structure. MeerKAT UHF-band (0.58--1.09 GHz) observations reveal a relic with a largest linear size of $\sim 1.48 \pm 0.02$ Mpc, located at a projected distance of 0.95 Mpc from the cluster centre. XMM-Newton X-ray data show that the relic's position and orientation relative to the intracluster medium (ICM) elongation are consistent with a merger-driven shock-wave scenario. The relic has an estimated radio power of $3.10 \pm 0.03 \times 10^{24}$ W Hz$^{-1}$ at 150 MHz. When placed in the $P_{150\,\mathrm{MHz}}$--$M_{500}$ scaling relation, the Abell 4067 relic appears less luminous compared to relics in more massive clusters, suggesting an association with weak merger shocks. This finding supports the idea that relics in low-mass clusters may form through less energetic merger events, leading to weak merger shocks. This is further supported by the absence of a detectable central radio halo in Abell 4067, reinforcing the idea that luminous radio halos are not a universal outcome of cluster mergers and highlighting the role of cluster mass, merger energetics, and evolutionary stage in shaping diffuse radio emission in the intracluster medium.