2019MNRAS.484.4174K

We present new synthesis models of the extragalactic background light (EBL) from far infra-red (FIR) to TeV γ-rays, with an emphasis on the extreme ultraviolet (UV) background that is responsible for the observed ionization and thermal state of the intergalactic medium across the cosmic time. Our models use updated values of the star formation rate density and dust attenuation in galaxies, QSO emissivity, and the distribution of HI gas in the intergalactic medium. Two of the most uncertain parameters in these models, the escape fraction of HI ionizing photons from galaxies and the spectral energy distribution (SED) of QSOs, are determined to be consistent with the latest measurements of HI and HeII photoionization rates, the HeII Lyman-α effective optical depths, various constraints on HI and HeII reionization history, and many measurements of the local EBL from soft X-rays till γ-rays. We calculate the EBL from FIR to TeV γ-rays by using FIR emissivities from our previous work and constructing an average SED of high-energy emitting QSOs, i.e, type-2 QSOs and blazars. For public use, we also provide the EBL models obtained using different QSO SEDs at extreme-UV energies over a wide range of redshifts. These can be used to quantify uncertainties in the parameters derived from photoionization models and numerical simulations originating from the allowed variations in the UV background radiation.