Carvalho, Lautaro
Argentina Instituto de Astronomía y Física del Espacio (IAFE) – UBA
Cosmic Rays at the Epoch of Reionization
The reionization of the intergalactic medium (IGM) during the Cosmic Dawn is an important open problem in Cosmology. The radiation produced by the first galaxies would not have been enough to maintain the ionization fraction of the IGM at large scales, therefore complementary ionization agents have been proposed, including cosmic rays (CR) that escape from those galaxies. In this poster, we investigate the ionization of the IGM produced by the electromagnetic cascades initiated by CR electrons, emphasizing the contribution of secondary photons, which has not been extensively explored yet. We simulated the transport of all the particles comprising the cascades and calculated the rate of ionization and the distribution of energy between the particles and the IGM. Our results show that high energy electrons carry energy far away from the source while ionizing the medium in their path, whilst those with kinetic energies lower than a few keV cool completely via ionization within a distance of kiloparsecs, reinforcing the results of previous works and extending their predictions to higher energy electrons and farther distances from the source. In addition, we show for the first time that photoionization by secondary photons produced in high-energy cascades may contribute significantly to the ionization of the IGM. This particular result implies a significant ionization rate in the far IGM that has not been considered by previous works. Finally, we evaluate the ionization rate at any point in the IGM in terms of the properties of the galaxy population present during the Cosmic Dawn as predicted by cosmological simulations of galaxy formation.