The Ultra-Low Frequency Universe

The ULU project will explore the largest scales of our Universe mapping one of the last uncharted observational windows of the cosmic electromagnetic spectrum: the ultra-low radio frequencies (10-100 MHz). Although these frequencies are crucial to unveil the nature and evolution of galaxy clusters, the complexity of such observations prevented their exploitation until now. Techniques I developed to analyse Low Frequency Array (LOFAR) data were able to overcome this limitation. With ULU we will survey the northern sky producing ultra-low frequency images that are 100 times more sensitive than the state-of-the-art. The legacy of ULU will be long lasting with a far reaching scientific outcome: from galaxy evolution to ionospheric science, from exoplanet habitability to the detection of the first galaxies at cosmic dawn.Within the ULU project, I will combine the survey with my expertise on the study of galaxy clusters. My group will adopt an innovative approach based on unveiling the full picture of the cosmic ray (CR) life-cycle in the intracluster medium, effectively combining diverse topics historically studied independently, such as the growth of structures, AGN activity, and galaxy evolution. While conventional radio frequencies are sensitive to emission generated by highly energetic CRs, with ULU we will explore the far larger domain of low-energy CRs that can be accelerated by still unexplored microphysical mechanisms. Furthermore, their emission can be observed over Gyr time scales, revealing the long-term actions and interactions of radio sources in cluster environments. With a full picture of the CR life-cycle we will 1. unveil how cluster merger energy is deposited in the intracluster medium through shocks, turbulence and other mechanisms, 2. measure the long-term effect of AGN feedback up to the age of cluster formation, and 3. make a realistic attempt at the characterisation of the WHIM properties and constrain the origin of cosmological magnetic fields.