Active Galactic Nuclei Jets Enriched by Wolf-Rayet Stars and Their Possible Contribution to Ultra-High-Energy Cosmic Rays

Despite all that we have learned from observational data, the sources of ultra-high-energy cosmic rays (UHECRs) have not yet been identified. Among the candidates discussed in the literature, starburst galaxies and active galactic nuclei (AGNs) are likely the most popular. Studies from the Pierre Auger Observatory indicate that the mass composition of particles with energies above $10^{19.3}$~eV is compatible with Carbon-Nitrogen-Oxygen (CNO) nuclei. While starburst galaxies contain the necessary CNO elements, their energy budget has been shown to be insufficient to accelerate UHECRs beyond $1$~EeV. In contrast, radiogalaxies, a subclass of AGNs, provide the required energy through their powerful jets. The lepton-dominated nature of these jets, however, makes the presence of nuclei nontrivial, requiring a mass-loading mechanism. One possible process for introducing nuclei into these jets is the interaction with embedded stars. In this work, we investigate the role of Wolf-Rayet (WRs) stars, which have CNO-rich winds, in supplying intermediate-mass nuclei to AGN jets. By exploring typical parameters for radiogalaxies, we estimate the resulting integrated UHECR flux and find solutions consistent with the flux measured by the Pierre Auger Observatory, suggesting that WR stars can supply sufficient CNO and heavier nuclei to be accelerated in AGN jets. We also discuss our results for the expected mass-composition fractions and the spectrum observed on Earth after propagation, particularly for Centaurus A.