Speaker
Description
We present the first study to investigate ultra-fast outflows (UFOs) of active galactic nuclei as potential sites for the production of the highest-energy cosmic rays, focusing on cosmic-ray nuclei, a previously unexplored aspect. These mildly-relativistic large-scale outflows, with velocities reaching up to half the speed of light, are ubiquitous in active galactic nuclei. We numerically study the processes that affect the maximum energy of the cosmic rays with 3D CRPropa simulations of the vicinity of the AGN. We then apply our method to 87 observed UFOs. We find that the studied UFOs can accelerate iron nuclei to $\sim10^{20}\,$eV, but only a small fraction of these sources allow the nuclei to escape, owing to photonuclear interactions with the intense photon fields within the AGN. The vast majority of the investigated outflows mainly allow protons and neutrons, which are either primary or byproducts of photodisintegration, to escape. Up to $50\%$ of the studied UFOs can contribute to the observed proton flux above $10^{18}\,$eV, depending on the strength of the extragalactic magnetic field, which imposes a magnetic horizon. We conclude that UFOs can supply the protons below the ankle of the cosmic-ray spectrum, making them intriguing source candidates for this component of the observed flux.
