Radio Galaxies as the Origin of Ultra-High-Energy Cosmic Rays

Abstract

Relativistic jets in radio galaxies (RGs) are considered a promising candidate for the acceleration sites of ultra-high-energy cosmic rays (UHECRs). To access this hypothesis, we first quantify the UHECRs produced at relativistic jets using relativistic hydrodynamic simulations for the evolution of RG jets and Monte Carlo simulations for the transport of cosmic ray particles. The strong shear produced at the jet-backflow boundary provides the main mechanism of UHECR acceleration, and the energy spectrum of the UHECRs escaping from RGs could be described by a double-power law with an exponential cutoff. We then predict the energy spectrum and composition of UHECRs arriving at the Earth from RGs, using simulations with the CRPropa3 code for the propagation of UHECRs through the intergalactic space. Finally, we model the Auger and TA observatories with UHECRs from nearby RGs as well as cosmologically distributed RGs, by estimating their relative importance. In this presentation, we present the results and argue that the energy spectrum and composition in the TA and Auger observations could be reasonably modeled with UHECRs produced at RGs.