Cosmic γ-ray background from structure formation in the intergalactic medium

Abraham Loeb () and Eli Waxman
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Abraham Loeb: Harvard-Smithsonian Center for Astrophysics
Eli Waxman: Weizmann Institute

Nature, 2000, vol. 405, issue 6783, 156-158

Abstract: Abstract The Universe is filled with a diffuse background of γ-ray radiation1, the origin of which remains one of the unsolved puzzles of cosmology. Less than one-quarter of the γ-ray flux can be attributed to unresolved discrete sources2,3, such as active galactic nuclei; the remainder appears to constitute a truly diffuse background. Here we show that the shock waves induced by gravity in the gas of the intergalactic medium, during the formation of large-scale structures like filaments and sheets of galaxies, produce a population of highly relativistic electrons. These electrons scatter a small fraction of the cosmic microwave background photons in the local Universe up to γ-ray energies, thereby providing the γ-ray background. The predicted diffuse flux agrees with the observed background across more than four orders of magnitude in photon energy, and the model predicts that the γ-ray background, though generated locally, is isotropic to better than five per cent on angular scales larger than a degree. Moreover, the agreement between the predicted and observed background fluxes implies a mean cosmological density of baryons that is consistent with Big Bang nucleosynthesis.

Date: 2000
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Persistent link: https://EconPapers.repec.org/RePEc:nat:nature:v:405:y:2000:i:6783:d:10.1038_35012018

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DOI: 10.1038/35012018

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