Combined Fit of Spectrum and Composition for FR0 Radio Galaxy Emitted Ultra-High-Energy Cosmic Rays with Resulting Secondary Photons and Neutrinos
arxiv(2024)
Abstract
This study comprehensively investigates the gamma-ray dim population of
Fanaroff-Riley Type 0 (FR0) radio galaxies as potentially significant sources
of ultra-high-energy cosmic rays (UHECRs, E > 10^18 eV) detected on
Earth. While individual FR0 luminosities are relatively low compared to the
more powerful Fanaroff-Riley Type 1 and Type 2 galaxies, FR0s are substantially
more prevalent in the local universe, outnumbering the more energetic galaxies
by a factor of ∼5 within a redshift of z ≤ 0.05.
Employing CRPropa3 simulations, we estimate the mass composition and energy
spectra of UHECRs originating from FR0 galaxies for energies above 10^18.6
eV. This estimation fits data from the Pierre Auger Observatory (Auger) using
three extensive air shower models; both constant and energy-dependent observed
elemental fractions are considered. The simulation integrates an isotropic
distribution of FR0 galaxies, extrapolated from observed characteristics, with
UHECR propagation in the intergalactic medium, incorporating various plausible
configurations of extragalactic magnetic fields, both random and structured. We
then compare the resulting emission spectral indices, rigidity cutoffs, and
elemental fractions with recent Auger results. In total, 25 combined energy
spectrum and mass composition fits are considered.
Beyond the cosmic ray fluxes emitted by FR0 galaxies, this study predicts the
secondary photon and neutrino fluxes from UHECR interactions with intergalactic
cosmic photon backgrounds. The multi-messenger approach, encompassing
observational data and theoretical models, helps elucidate the contribution of
low luminosity FR0 radio galaxies to the total cosmic ray energy density.
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