Assessing the origin of the extragalactic neutrino background with new cosmological simulations

The extragalactic neutrino background is a diffuse emission with unknown origin ranging between 10 TeV and 2 PeV in energy. Different classes of sources have been suggested as potential contributors to the background, among these: Active Galactic Nuclei, Star Forming Galaxies and cosmic shocks. My Thesis work has the goal of understanding the contributions of cosmic populations to the neutrino background through the employment of cosmological magneto-hydrodynamical simulations using ENZO. Such simulations are designed to investigate the injection and evolution of cosmic rays by different mechanisms operating in the cosmic web. They cover a comoving volume of (42.5M pc)3 with a static grid of cells with a constant spatial resolution of 41.5 kpc/cell. Cosmic rays are injected at runtime by simulated jetted AGN, star formation and cosmic shocks and are assumed to generate neutrinos and gamma-rays through proton-proton interactions. These simulations allow me to compute the neutrino and gamma-ray fluxes, based on the formalism developed by Pfrommer and Ensslin (2004). I computed the cumulative neutrino and gamma ray fluxes taking into account redshift dependent corrections in order to generate a realistic model for the full sky background in the energy bands 0.5 − 200 GeV for the gamma-rays and 10^5 − 10^6 GeV for the neutrinos. I compared the simulated cumulative gamma ray fluxes with the Fermi-Large Area Telescope (LAT) limit and the cumulative neutrino flux with the IceCube obseravtory limit. I found that, in order for the gamma-ray emission to be consistent with the Fermi-LAT limit, the injection efficiency of AGN and cosmic shocks in the simulation should be decreased by at least a factor 6. Once this effect is taken into account, the main contributors to the neutrino background are found to be AGN. The results show that AGN, star-formation and cosmic shocks are responsible for the entirety of the gamma-ray emission, but only for a fraction of the neutrino emission