Implications of Cosmological Gamma-Ray Absorption - I.Evolution of the Metagalactic Radiation Field

TL;DR

This paper presents a semi-empirical model of the evolving metagalactic radiation field based on galaxy observations, enabling better estimates of gamma-ray absorption and attenuation lengths across cosmic history.

Contribution

It introduces a minimal-parameter model for the cosmic radiation field that incorporates galaxy survey data and accounts for infrared galaxy contributions, improving gamma-ray absorption predictions.

Findings

The model's intensity predictions are independent of cosmological parameters.

The far-infrared background discrepancy is addressed by including luminous infrared galaxies.

The model reliably estimates gamma-ray attenuation lengths up to redshift 5.

Abstract

Gamma-ray absorption due to gamma-gamma-pair creation on cosmological scales depends on the line-of-sight integral of the evolving density of low-energy photons in the Universe, i.e. on the history of the diffuse, isotropic radiation field. Here we present and discuss a semi-empirical model for this metagalactic radiation field based on stellar light produced and reprocessed in evolving galaxies. With a minimum of parameters and assumptions, the present-day background intensity is obtained from the far-IR to the ultraviolet band. Predicted model intensities are independent of cosmological parameters, since we require that the comoving emissivity, as a function of redshift, agrees with observed values obtained from deep galaxy surveys. The far-infrared background at present day prediced from optical galaxy surveys falls short in explaining the observed one, and we show that this deficit can be removed by taking into account (ultra)luminous infrared galaxies (ULIGs/LIGs) with a seperate star formation rate. The accuracy and reliability of the model, out to redshifts of 5, allow a realistic estimate of the attenuation length of GeV-to-TeV gamma-rays and its uncertainty, which is the focus of a subsequent paper.