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Spatial variations of the average properties that characterize the hadroniccomponent of the diffuse Galactic cosmic-ray sea, in particular the spectralslope and normalization, may unveil critical information about theirconfinement mechanism in the Galaxy. In the first part of this paper we performan analysis of the Fermi-LAT gamma-ray data with the SkyFACT package, whichcombines image reconstruction techniques with standard template fitting,isolate the hadronic emission and decompose it into Galactocentric rings. Wefind a significant hardening of the hadronic spectral index towards themolecular ring. We study this hardening in different energy ranges, and assessits resilience with respect to different prescriptions in the analysis setup.In the second part we quantify the contribution to the diffuse gamma-ray fluxcoming from unresolved point sources with a dedicated Monte Carlo simulation,and consider whether the trend characterized in the first part can be mimickedby a progressively more relevant flux associated to this component in the innerGalaxy. We find that the observed hardening of the hadronic spectral indexcannot be due to unresolved sources in the sub-TeV energy range, especiallyoutside the molecular ring, given reasonable assumptions about the unresolvedsource population.

On the progressive hardening of the cosmic-ray proton spectrum in the inner Galaxy