PROFESSOR RUTA KALE

Clusters of galaxies are the Universes' most massive gravitational potential wells that hold large reservoirs of baryons in the form of diffuse gas called the intra-cluster medium (ICM). The ICM is mainly thermal gas of temperature ~ten million Kelvin that is weakly magnetised with field strengths of 0.1 - a few micro Gauss. The cosmic rays and magnetic fields, referred to as the non-thermal components, elude detection in most spectral bands and thus have remained the least understood components of the ICM. The relativistic electrons in the ICM manifest the non-thermal components at low radio frequencies (<= GHz) via synchrotron radiation providing a direct probe of their life cycles. From the radio surveys with the GMRT in the past few years, it has emerged that cluster mass and re-acceleration of seed relativistic electrons by shocks and turbulence are the factors important in the generation of the megaparsec-scale diffuse radio sources termed as radio halos, mini-halos and relics. Cluster mergers are responsible for driving shocks and turbulence in the ICM and the hadronic collisions and radio galaxies are the likely sources of the seed relativistic electrons. Although cluster mergers and radio galaxies are fairly common in massive clusters the rarity of the diffuse radio sources indicates the gaps in our understanding. With the Upgraded Giant Metrewave Radio Telescope (uGMRT) it is now possible to make radio images that are a factor of a few better in sensitivity than the GMRT and to obtain a well sampled spectrum across the frequency range of 150 - 1400 MHz. I will describe our discoveries of diffuse sources and results towards characterising the cosmic rays and magnetic fields with the uGMRT to unravel the details on the connection between cluster mergers and the re-acceleration mechanisms.