Using the Extragalactic Gamma-Ray Background to Constrain the Hubble Constant and Matter Density of the Universe

Abstract

Abstract The attenuation produced by extragalactic background light (EBL) in γ-ray spectra of blazars has been used to constrain the Hubble constant (H 0) and matter density (Ωm) of the universe. We propose to estimate H 0 and Ωm using the well-measured >10 GeV extragalactic γ-ray background (EGB). This suggestion is based on the fact that the >10 GeV EGB is totally explained by the emissions from blazars, and an EBL-absorption cutoff occurs at ∼50 GeV in the EGB spectrum. We fit the >10 GeV EGB data with modeled EGB spectrum. This results in and . Note that the uncertainties may be underestimated due to the limit of our realization for EBL model. H 0 and Ωm are degenerate in our method. Independent determination of Ωm by other methods would improve the constraint on H 0.