The role of Galactic unresolved PWNe to the gamma-ray diffuse emission

We discuss the implications of the TeV galactic PulsarWind Nebulae (PWNe) population observed by HESS Galactic Plane Survey (HGPS) for the interpretation of Fermi-LAT data in the GeV domain. We show that consistency among HGPS and 3FGL catalogs requires that the average ratio R-Phi = Phi(GeV) /Phi(TeV), where Phi(GeV) (Phi(TeV)) is the integrated gamma-ray flux emitted by sources in the range 1-100 GeV(1-100 TeV) probed by Fermi-LAT (HESS), is R-Phi = 500 1000. Considering that the average spectral index of observed sources at TeV energies is beta(TeV) = 2.3, the required value for R-Phi can be only obtained by assuming that sources have spectral break below 1 TeV and harder emission spectrum with beta(GeV) < 2 in the GeV domain. Such spectral shapes are well compatible with the expected gamma-ray emission in young PWNe due to Inverse Compton scattering of high-energy electrons on background radiation fields. Finally, we show that a relevant fraction of the TeV source population cannot be resolved by Fermi-LAT in the GeV domain. We suggest that unresolved sources can provide a not negligible contribution to the large-scale diffuse emission observed by Fermi-LAT, possibly explaining the spectral hardening of this component toward the galactic center reported by Gaggero et al. 2018, Yang et al. 2016, Acero et al. 2016.