GeV gamma-ray attenuation and the high-redshift UV background |
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| Authors: | Rudy C Gilmore Piero Madau Joel R Primack Rachel S Somerville Francesco Haardt |
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| Institution: | Department of Physics, University of California, Santa Cruz, CA 95064, USA;Department of Astronomy &Astrophysics, University of California, Santa Cruz, CA 95064, USA;Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA;Dipartimento di Fisica e Matematica, Universitádell'Insubria, Via Valleggio 11, 22100 Como, Italy |
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| Abstract: | We present new calculations of the evolving UV background out to the epoch of cosmological reionization and make predictions for the amount of GeV gamma-ray attenuation by electron–positron pair production. Our results are based on recent semi-analytic models of galaxy formation, which provide predictions of the dust-extinguished UV radiation field due to starlight, and empirical estimates of the contribution due to quasars. We account for the reprocessing of ionizing photons by the intergalactic medium. We test whether our models can reproduce estimates of the ionizing background at high redshift from flux decrement analysis and proximity effect measurements from quasar spectra, and identify a range of models that can satisfy these constraints. Pair production against soft diffuse photons leads to a spectral cut-off feature for gamma rays observed between 10 and 100 GeV. This cut-off varies with redshift and the assumed star formation and quasar evolution models. We find only negligible amounts of absorption for gamma rays observed below 10 GeV for any emission redshift. With observations of high-redshift sources in sufficient numbers by the Fermi Gamma-ray Space Telescope and new ground-based instruments, it should be possible to constrain the extragalactic background light in the UV and optical portion of the spectrum. |
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| Keywords: | intergalactic medium gamma rays: bursts cosmology: theory gamma rays: theory diffuse radiation ultraviolet: galaxies |
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