Astronomers have detected a peculiar mini-halo of diffuse radio emission in the galaxy cluster Abell 3558. The finding was made using multi-band radio observations conducted with the MeerKAT and Upgraded Giant Metrewave Radio Telescope. The team, led by Keegan Trehaeven of Rhodes University, aimed to understand the origin of the emission.
Abell 3558 is a massive galaxy cluster at a redshift of 0.047, containing thousands of galaxies bound together by gravity. Previous observations have revealed mixed characteristics in its intracluster medium and significant diffuse radio emission in the cluster center. The researchers conducted deep observations with different frequency bands to disentangle the origin of the emission.
The team found that the diffuse radio emission has a radio power of 68 ZW/Hz at 1.4 GHz and is more extended than previously thought, stretching up to 1.8 million light years. They identified a faint northern extension beyond the innermost cold front, increasing the projected size of the emission.
The study showed that the investigated emission has an integrated spectral index of 1.18, with a flatter spectrum just inside the X-ray cold front and a steeper spectrum outside. This suggests local turbulent re-acceleration and larger-scale sloshing turbulence, powered by gas sloshing and/or active galactic nucleus (AGN) feedback processes.
The astronomers concluded that the observed diffuse radio emission is a radio mini-halo, likely confined by cold fronts in the core. Radio mini-halos are typically found in dynamically relaxed systems with cool-cores, where no major merger event has occurred. This discovery provides insights into galaxy evolution and cosmology.
Source: https://phys.org/news/2025-07-galaxy-cluster-abell-peculiar-mini.html