An Empirical Determination of the Intergalactic Background Light From Uv to Fir Wavelengths Using Fir Deep Galaxy Surveys and the Gamma-Ray Opacity of the Universe

Abstract

We have previously calculated the intergalactic background light (IBL) as a function of redshift from the Lyman limit in the far-ultraviolet to a wavelength of 5 μm in the near-infrared range, based purely on data from deep galaxy surveys. Here, we use similar methods to determine the mid-and far-infrared IBL from 5 to 850 μm. Our approach enables us to constrain the range of photon densities by determining the uncertainties in observationally determined luminosity densities and spectral gradients. By also including the effect of the 2.7 K cosmic background photons, we determine upper and lower limits on the opacity of the universe to γ-rays up to PeV energies within a 68% confidence band. Our direct results on the IBL are consistent with those from complimentary γ-ray analyses using observations from the Fermi γ-ray space telescope and the H.E.S.S. air Čerenkov telescope. Thus, we find no evidence of previously suggested processes for the modification of γ-ray spectra other than that of absorption by pair production alone.

Measurement of the EBL spectral energy distribution using the VHE γ-ray spectra of H.E.S.S. blazars

“…The results are also in general agreement with other constraints not represented in Fig. 5 obtained using γ rays (Abramowski et al 2013b;Ahnen et al 2016) or with the results of empirical approaches to the determination of the EBL SED (Helgason & Kashlinsky 2012;Stecker et al 2016).…”

EBL effect on the observation of multi-TeV flaring of 2009 from Markarian 501

“…It has been observed that the jet medium is transparent to pair production where the optical depth is very small [14,15]. Also the TeV photons on their way to Earth can interact with the extragalactic background light (EBL) to produce the lepton pair [16][17][18][19][20].…”

Attenuation of TeV γ-rays by the starlight photon field of the host galaxy

“…Taking into account the uncertainty in the EBL models, the absorption by the EBL starts to dominate the absorption by the host galaxy in sources with a redshift zr > 0.015. Calculations by Stecker et al (2016) indicate that the EBL-absorption of 2 TeV photons from a source at zr = 0.015 is at a level of τEBL = 0.15 ± 0.06, where the uncertainty is derived from the observational uncertainty of EBL measurements. The absorption by starlight dominates in sources with a smaller redshift.…”

“…The level of the EBL is not precisely known. The values of τEBL are subject to non-negligible uncertainty (e.g., Stecker et al 2016). Hence, the effect of EBL contributions cannot be corrected in observed data.…”