The Galactic diffuse gamma ray emission in the energy range 30 TeV - 3 PeV

The new generation gamma ray telescopes, such as LHAASO, HISCORE and CTA will have a much larger sensitivity at energies above 30 TeV with respect to the current instruments, allowing the study of the gamma ray sky in an energy range almost completely unexplored. The observations will focus both on individual gamma ray sources and (in case of large field of view detectors like air shower arrays) on diffuse emissions, such as the radiation generated by cosmic ray interactions in the interstellar medium. In this energy range the absorption effects due to pair production, when the gamma rays interact with the radiation fields present in space, effectively prevent the observations of extragalactic sources, but are also significant for Galactic photons. In this paper we describe different predictions for the diffuse Galactic emission in the energy range [30 TeV, 3 PeV], that are based on extrapolations of the observations at lower energy, and also include the possibility that a non negligible fraction of the IceCube signal of astrophysical neutrinos is of Galactic origin, and has a gamma ray counterpart. A detailed modeling of the effects of gamma ray absorption is required for a correct interpretation of the observations, because the absorption, that strongly depends on the distance and direction of the emission point, modifies the spectral shape, and distorts the angular distribution of the observed flux. In this work we discuss the potential of the future observatories for the study of the Galactic gamma ray diffuse emission, and the importance of these studies for our understanding the properties of Galactic cosmic rays.