A parametrized catalog of radio galaxies as UHECR sources
2019 July 30
Many attempts have been made to provide catalogs of potential sources of ultra-high energy cosmic rays (UHECR) based on various astronomical tracers, such as observed radio or gamma-ray emission. A closer look reveals, however, that they all suffer from significant bias and selection effects. We present here a demo-version of a catalog for one often-discussed UHECR source class, radio galaxies (or radio-loud AGN), which is based on a complete theoretical description of jet-energetics, particle acceleration physics, relativistic beaming effects and nuclear composition, parametrized by a comprehensible set of adjustable physical quantities. As found in previous work, the FR-II galaxy Cygnus A at ~250 Mpc distance is expected to be the strongest UHECR contributor in the sky, but in our new sample it is almost matched by the equally distant steep spectrum radio quasar PKS 0521-36 if relativistic beaming effects are considered. Under the assumption that the contribution of Cygnus A is significantly diminished — because it is too young (<10Myr) for its cosmic rays to reach us due to their delay in the propagation through extragalactic magnetic fields (EGMF) — we find that the anisotropy signals expected from radio galaxies promise to be in good agreement with current observational findings. Yet, in particular the current lack of knowledge of the EGMF strength leaves big scope for predictions. We plan to provide a completed and improved version of this catalog in electronic form, to be used in more detailed UHECR propagation simulations. For immediate applications, we suggest a complete set of 15 strong UHECR sources which can contribute to UHECR anisotropy on the level which can be currently probed by experiment, and note that 5 of them have not been considered in any previous studies.