Volume 386, Number 1, April IV 2002
|Page(s)||1 - 11|
|Published online||15 April 2002|
Implications of cosmological gamma-ray absorption
I. Evolution of the metagalactic radiation field
Universität Würzburg, Am Hubland, 97057 Würzburg, Germany
2 Clemson University, Clemson, SC 29634-0978, USA
Corresponding author: T. M. Kneiske, firstname.lastname@example.org
Accepted: 30 January 2002
Gamma-ray absorption due to -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 predicted 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 with a seperate star formation rate. The accuracy and reliability of the model, out to redshifts of , allow a realistic estimate of the attenuation length of GeV-to-TeV gamma-rays and its uncertainty, which will be the focus of a subsequent paper.
Key words: galaxies: evolution / ISM: general / radiation mechanisms: general / cosmology: observations
© ESO, 2002
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