Galaxy formation simulations demonstrate that cosmic-ray ( CR ) feedback may be important in the launching of galactic-scale winds .
CR protons dominate the bulk of the CR population , yet most observational constraints of CR feedback come from synchrotron emission of CR electrons .
In this paper , we present an analysis of 105 months of Fermi Gamma-ray Space Telescope observations of the Small Magellanic Cloud ( SMC ) , with the aim of exploring CR feedback and transport in an external galaxy .
We produce maps of the 2 - 300 GeV emission and detect statistically significant , extended emission along the “ Bar ” and the “ Wing ” , where active star formation is occurring .
Gamma-ray emission is not detected above \sim 13 GeV , and we set stringent upper-limits on the flux above this energy .
We find the best fit to the gamma-ray spectrum is a single-component model with a power-law of index \Gamma = -2.11 \pm 0.06 \pm 0.06 and an exponential cutoff energy of E _ { c } = 13.1 \pm 5.1 \pm 1.6 GeV .
We assess the relative contribution of pulsars and CRs to the emission , and we find that pulsars may produce up to 14 ^ { +4 } _ { -2 } % of the flux above 100 MeV .
Thus , we attribute most of the gamma-ray emission ( based on its spectrum and morphology ) to CR interactions with the ISM .
We show that the gamma-ray emissivity of the SMC is five times smaller than that of the Milky Way and that the SMC is far below the “ calorimetric limit ” , where all CR protons experience pion losses .
We interpret these findings as evidence that CRs are escaping the SMC via advection and diffusion .