Diffuse Extragalactic Background Radiation

TL;DR

This paper presents semi-analytic models linking galaxy formation and evolution with high-energy gamma-ray attenuation, providing insights into cosmic history and the role of galaxy emissivities in gamma-ray astronomy.

Contribution

The study introduces two galaxy evolution models that bracket the range of galaxy emissivities and analyze their impact on gamma-ray optical depth across redshifts.

Findings

Models successfully reproduce observational galaxy properties.

Optical depth varies with redshift and gamma-ray energy.

Implications for gamma-ray astronomy and cosmology are discussed.

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 $\Lambda$CDM hierarchical 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 gamma-ray astronomy will continue to help constrain cosmology.