High-Energy Neutrinos and Gamma-rays from the Milky Way

Hadronic interactions of high energy protons (or nuclei) with ambient medium represent one of the main processes that produce high-energy neutrinos and TeV gamma-rays in our Galaxy. They occur both within the sources where cosmic rays (CR) are accelerated and/or in the interstellar gas contained in our Galaxy. Being gamma and neutrino production strictly related, it is natural to adopt a multimessenger approach in which their observations are explained within the same framework. We present updated calculations of the diffuse emission produced by the interaction of CR with the gas contained in the Galactic disk considering also the possibility of CR spectral hardening in the inner Galaxy, recently emerged from the analysis of Fermi-LAT data at lower energies. Above TeV energies diffuse and source components are expected to provide comparable contributions and it is difficult to separate them on observational grounds. Hence we compare our estimates with the total (diffuse + sources) observed fluxes: IceCube HESE signal for neutrinos, and fluxes from the Galactic plane measured by Argo-YBJ, H.E.S.S., HAWC and Milagro for the gamma counterpart. We provide a limit to the fraction of the high energy neutrino signal observed by IceCube that can be ascribed to a Galactic origin. We demonstrate that the TeV gamma-ray sky can be used to probe the distribution of Galactic cosmic rays. We state that a potential tension exists between the CR spectral hardening hypothesis and observational results. The constraints can be strengthened if the contribution of sources not resolved by H.E.S.S. is taken into account. The analysis of H.E.S.S. Galactic Plane Survey allows to infer the properties of Galactic TeV source population. Evaluating the cumulative flux expected at Earth by the considered population, we show that the H.E.S.S. unresolved sources provide a relevant contribution to the diffuse Galactic emission. By the population study we infer general information on the total Milky Way such as its high-energy gamma-ray luminosity and total flux. Finally, in the hypothesis that the majority of bright sources detected by H.E.S.S. are powered by pulsar activity, like e.g. pulsar wind nebulae or TeV halos, we estimate the main properties of the pulsar population.