Much of the evolution of galaxies before they are assimilated into clusters occurs in groups where AGN feedback has the greatest impact on galaxy formation and evolution. Conversely, clusters are the largest gravitationally bound structures in the Universe, with radio observations being powerful tools for detecting diffuse cluster-scale synchrotron emission, which conveys information about the cluster formation history.
In the first part of this talk, I will summarize results from studies of the central brightest group early-type galaxies (BGEs) of an optically selected, statistically complete sample of 53 nearby groups (<80 Mpc; CLoGS sample), observed in radio 235/610 MHz (GMRT), CO (IRAM/APEX) and X-ray (Chandra and XMM-Newton) frequencies examining the balance between hot and cold gas (AGN feedback) and the AGN activity and star formation in groups, presenting also updated results from MeerKAT L-Band observations.
In the second part, I will summarise results from the recently published MeerKAT’s Galaxy Cluster Legacy Survey (MGCLS) diffuse radio emission catalogue work (Kolokythas et al. 2025), a project which originally comprised the first MeerKAT L-Band long-track observations of 115 galaxy clusters at 1.28 GHz across the Southern sky. I will focus on the detection rates, statistics, discoveries, and properties of the various diffuse radio emission structures detected in MGCLS galaxy clusters, which reveal new areas of investigation in cluster formation and evolution that pave the way for the SKA era.