Inverse Compton Contribution to the Star-Forming Extragalactic Gamma-Ray Background

Understand

Fermi has resolved several star-forming galaxies, but the vast majority of the star-forming universe is unresolved and thus contributes to the extragalactic gamma ray background (EGB).

• Here, we calculate the contribution from star-forming galaxies to the EGB in the Fermi range from 100 MeV to 100 GeV, due to inverse-Compton (IC) scattering of the interstellar photon field by cosmic-ray electrons.
• We first construct a one-zone model for a single star-forming galaxy, assuming supernovae power the acceleration of cosmic rays.
• The same IC interactions leading to gamma rays also substantially contribute to the energy loss of the high-energy cosmic-ray electrons.