An Empirical Determination of the Intergalactic Background Light from UV to FIR Wavelengths Using FIR Deep Galaxy Surveys and the Gamma-ray Opacity of the Universe

TL;DR

This paper empirically determines the intergalactic background light across UV to FIR wavelengths using galaxy surveys and gamma-ray observations, providing constraints on universe opacity and gamma-ray absorption.

Contribution

It extends previous UV-NIR IBL measurements to mid- and far-infrared, constraining photon densities and gamma-ray opacity up to PeV energies based on observational data.

Findings

Consistent IBL measurements with gamma-ray analyses.

No evidence for additional gamma-ray spectrum modifications.

Provides upper and lower limits on gamma-ray universe opacity.

Abstract

We have previously calculated the intergalactic background light (IBL) as a function of redshift in the far ultraviolet to near infrared range, based purely on data from deep galaxy surveys. Here we utilize similar methods to determine the mid- and far infrared IBL out to a wavelength of 850 microns. Our approach enables us to constrain the range of photon densities, based on the uncertainties from observationally determined luminosity densities and colors. By also including the effect of the 2.7 K cosmic background photons, we determine 68% confidence upper and lower limits on the opacity of the universe to gamma-rays up to PeV energies. Our direct results on the IBL are consistent with those from complimentary gamma-ray analyses using observations from the Fermi $\gamma$-ray space telescope and the H.E.S.S. air Cherenkov telescope. Thus, we find no evidence of previously suggested processes for the modification of gamma-ray spectra other than that of absorption by pair production alone.