Insights from LHAASO and IceCube into the origin of the Galactic diffuse teraelectronvolt-petaelectronvolt emission

High-energy diffuse gamma-ray and neutrino emission are expected from the Galactic plane, generated by hadronuclear interactions between cosmic rays and the interstellar medium. Therefore, measurements of this diffuse emission will provide important clues to the origin and nature of Galactic cosmic rays. Comparing the latest observations of the Large High-Altitude Air Shower Observatory and IceCube on diffuse Galactic gamma-ray and neutrino emission, respectively, we suggest that the diffuse gamma-ray emission at multi-teraelectronvolt energies contains a considerable leptonic component. By modelling the gamma-ray halos powered by middle-aged pulsars in our Galaxy, taking into account the magnetic field configuration and the interstellar radiation field in the Galaxy, we demonstrate that the collective contribution of pulsar halos can account for the excess in the measured diffuse gamma-ray emission with respect to the predicted flux from cosmic-ray-interstellar medium interactions. A joint analysis of the diffuse gamma-ray and neutrino emissions in the Galaxy shows that there is a non-negligible leptonic component in the diffuse gamma-ray emission below 100 TeV that is contributed by pulsar halos.