Very-high-energy γ-rays from Active Galactic Nuclei and the astroparticle connection

Research on ultra-high-energy cosmic rays and on TeV -rays investigates the most energetic phenomena in the Universe. Connections between these two fields are not only given by the common indirect detection methods, but also by the possibility of common astrophysical sources. Among the very few objects proposed as sites for the acceleration of ultra-high-energy cosmic rays, Active Galactic Nuclei (AGNs) are still prime candidates. They also represent the almost exclusive class of extragalactic sources detected at the highest observable photon energies with ground-based Cherenkov telescopes. The present document proposes an overview of a few selected observations of AGNs of the blazar class seen in TeV -rays with the H.E.S.S. experiment, together with interpretations of their multi-waveband emission based on different radiative transfer models. A special emphasis is put on so-called hadronic models, which try to provide a direct link between the observed electromagnetic emission and a possible accompanying ux of highly energetic cosmic rays and neutrinos. The future of very-high-energy astronomy will be determined by the first open observatory in this domain, the Cherenkov Telescope Array. The ongoing preparation of this project is described, with a focus on the simulations of air showers and telescopes, necessary to determine its performance, and on the science case for AGNs