2021MNRAS.506.5389P

Low-mass (M₅₀₀ < 5 x 10¹⁴ M_☉) galaxy clusters have been largely unexplored in radio observations, because of the inadequate sensitivity of existing telescopes. However, the upgraded Giant Metrewave Radio Telescope (uGMRT) and the Low Frequency ARray (LoFAR), with unprecedented sensitivity at low frequencies, have paved the way to study less massive clusters more closely than before. We have started the first large-scale programme to systematically search for diffuse radio emission from low-mass galaxy clusters, chosen from the Planck Sunyaev-Zel'dovich cluster catalogue. We report here the detection of diffuse radio emission from four of the 12 objects in our sample, shortlisted from the inspection of the LoFAR Two-Meter Sky Survey data release 1 (LoTSS-I), followed up by uGMRT Band 3 deep observations. The clusters PSZ2 G089 (Abell 1904) and PSZ2 G111 (Abell 1697) are detected with relic-like emission, while PSZ2 G106 is found to have an intermediate radio halo and PSZ2 G080 (Abell 2018) seems to be a halo-relic system. PSZ2 G089 and PSZ2 G080 are among the lowest-mass clusters discovered with a radio-relic and a halo-relic system, respectively. A high (∼30 per cent) detection rate, with powerful radio emission (P_1.4 GHz_ ∼ 10²³ W Hz^–1) found in most of these objects, opens up prospects of studying radio emission in galaxy clusters over a wider mass range, to much lower-mass systems.