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

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 ~1.48 ± 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 ± 0.03 × 1024 W Hz−1 at 150 MHz. When placed in the P150 MHz-M500 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. The latter is supported by the absence of a detectable central radio halo in Abell 4067, which reinforces the idea that luminous radio halos are not a universal outcome of cluster mergers and highlights the role of cluster mass, merger energetics and evolutionary stage in shaping diffuse radio emission in the intracluster medium.