A new derivation of the Hubble constant from γ -ray attenuation using improved optical depths for the Fermi and CTA era

Abstract

We present γ -ray optical-depth calculations from a recently published extragalactic background light (EBL) model built from multiwavelength galaxy data from the Hubble Space Telescope Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (HST/CANDELS). CANDELS gathers one of the deepest and most complete observations of stellar and dust emissions in galaxies. This model resulted in a robust derivation of the evolving EBL spectral energy distribution up to z ∼ 6, including the far-infrared peak. Therefore, the optical depths derived from this model will be useful for determining the attenuation of γ -ray photons coming from high-redshift sources, such as those detected by the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope, and for multi-TeV photons that will be detected from nearby sources by the future Cherenkov Telescope Array. From these newly calculated optical depths, we derive the cosmic γ -ray horizon and also measure the expansion rate and matter content of the Universe including an assessment of the impact of the EBL uncertainties. We find H0 = 62.4 +−3491 km s−1 Mpc−1 when fixing Ωm = 0.32, and H0 = 65.1 +−4690 km s−1 Mpc−1 and Ωm = 0.19 ± 0.08, when exploring these two parameters simultaneously.