Coffee talks
Friday 27/06/2025 @ 11:30, Sala riunioni quarto piano e on-line (meet.google.com/sue-bwvk-axf)
Sameer Salunkhe (National Centre for Radio Astrophysics, Pune, India), "Probing the large scale structures with SKA pathfinder and precursor"
Diffuse radio emission in galaxy clusters traces the non-thermal components of the intracluster medium (ICM), including magnetic fields and relativistic electrons. Radio observations reveal extended structures—such as halos, relics, and mini-halos—driven by turbulence and shocks during large-scale structure formation. These phenomena offer crucial insights into particle acceleration processes in magnetized plasma. I will discuss the discovery of a radio megahalo in the merging galaxy cluster PLCKG287.0+32.9, based on deep uGMRT observations. The diffuse central emission extends to ?3.2 Mpc, reaching the cluster’s R500. The surface brightness profile shows a clear flattening beyond ?0.5 R500, while the outer envelope has a steep spectral index (? ?1.5) and ?20 times lower emissivity than the core—confirming its megahalo nature. The emission’s alignment with the merger axis supports a turbulence-driven re-acceleration scenario, consistent with recent simulations. This is the first detection of such a structure above 144 MHz, opening new avenues for spectral studies. I will also present the results from the GEMSS survey (Galaxy Evolution and Magnetization of the Saraswati Supercluster), based on MeerKAT L-band observations over ? 12 deg2. A catalog of radio sources above the 5? threshold was generated, including cluster-scale diffuse sources. Cross-matching with uGMRT Band-3 data revealed spectral flattening at low flux densities, indicating a larger population of star-forming galaxies and compact AGN. The Euclidean normalized source counts align with models, offering insights into the evolving radio galaxy population. Together, these results demonstrate the power of SKA pathfinders and precursors in probing galaxy evolution, diffuse emission and particle acceleration in large-scale cosmic structures.