Diffuse Extragalactic Background Radiation

Abstract

Attenuation of high—energy gamma rays by pair—production with UV, optical and IR background photons provides a link between the history of galaxy formation and high—energy astrophysics. We present results from our latest semi‐analytic models (SAMs), based upon a ΛCDM hierachical structural formation scenario and employing all ingredients thought to be important to galaxy formation and evolution, as well as reprocessing of starlight by dust to mid‐ and far‐IR wavelengths. Our models also use results from recent hydrodynamic galaxy merger simulations. These latest SAMs are successful in reproducing a large variety of observational constraints such as number counts, luminosity and mass functions, and color bimodality. We have created 2 models that bracket the likely ranges of galaxy emissivities, and for each of these we show how the optical depth from pair—production is affected by redshift and gamma‐ray energy. We conclude with a discussion of the implications of our work, and how the burgeoning science of...