Probing the transition between Galactic and extragalactic cosmic rays with a multi-messenger approach

The transition energy between Galactic and extragalactic cosmic rays remains an open question. Thanks to the new generation of observatories, observational windows have opened in PeV energies in neutrinos (IceCube, GVD and KM3NeT) and gamma rays (HAWC, LHAASO), complementing CR measurements in this energy range. This expanded dataset provides a more comprehensive framework for investigating the origins of CRs. This study seeks to constrain the extragalactic cosmic ray populations that propagate in the Milky Way, using cosmic rays and a multi-messenger approach: we model the distribution of extragalactic cosmic rays in the Milky Way and compute the spectra of gamma rays and neutrinos produced during their propagation. For our first toy model, we injected a pure proton spectrum, matching local measurement. The resulting intensity of gamma rays and neutrinos is found to be well below diffuse measurements and associated limits: our simple model cannot be ruled out by available measurements.