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arXiv · 0811.1984

Modeling Gamma-Ray Attenuation in High-Redshift GeV Spectra

Rudy C. Gilmore·Piero Madau·Joel R. Primack·Rachel S. Somerville
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Abstract

We present two models for the cosmological UV background light, and calculate the opacity of GeV gamma--rays out to redshift 9. The contributors to the background include 2 possible quasar emissivities, and output from star--forming galaxies as determined by recent a semi--analytic model (SAM) of structure formation. The SAM used in this work is based upon a hierarchical build-up of structure in a $Λ$CDM universe and is highly successful in reproducing a variety of observational parameters. Above 1 Rydberg energy, ionizing radiation is subject to reprocessing by the IGM, which we treat using our radiative transfer code, CUBA. The two models for quasar emissivity differing above z = 2.3 are chosen to match the ionization rates observed using flux decrement analysis and the higher values of the line-of-sight proximity effect. We also investigate the possibility of a flat star formation rate density at z $>5$. We conclude that observations of gamma--rays from 10 to 100 GeV by Fermi (GLAST) and the next generation of ground based experiments should confirm a strongly evolving opacity from $1<$ z $<4$. Observation of attenuation in the spectra of gamma--ray bursts at higher redshift could constrain emission of UV radiation at these early times, either from a flat or increasing star-formation density or an unobserved population of sources.

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Rudy C. Gilmore, Piero Madau, Joel R. Primack, Rachel S. Somerville. 2008-11-12. Modeling Gamma-Ray Attenuation in High-Redshift GeV Spectra. https://doi.org/10.1063/1.3076738

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