A TeV-based Determination of the Local Extragalactic Background Light and Its Consistency with Galaxy Counts and Direct Measurements

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Abstract
The extragalactic background light (EBL), the cumulative radiation from all extragalactic sources, traces galaxy formation and cosmic evolution. High-energy γ -rays attenuated via pair production with EBL photons are a powerful probe of the EBL. In this work, we use very-high-energy (VHE; E γ > 100 GeV) γ -rays to measure the local EBL intensity and test its consistency with galaxy counts and direct measurements. Our analysis employs a sample of 286 spectra from 45 sources observed with Imaging Atmospheric Cherenkov telescopes. A model-dependent study shows seven EBL templates require only ≤10% rescaling to fit the observed γ -ray attenuation. The galaxy-count-anchored model gives the closest match. We then derive template-marginalized TeV optical depths from a representative model subset. We combine them with Fermi-LAT GeV measurements to reconstruct the EBL at z = 0 using empirical and physically motivated models. The two reconstructions agree and follow the integrated galaxy light to within 2–3 nW m −2 sr −1 (typically μ m. Both are consistent with low-zodiacal-light observations, including outer solar system and dark cloud measurements. In contrast, the near-IR excess reported by the Infrared Telescope in Space and CIBER exceeds our reconstructed intensity by 3 σ –5 σ , implying an additional ≳5–10 nW m −2 sr −1 incompatible with the γ -ray optical depths. Combined with GeV constraints on EBL evolution to z ≃ 4, these TeV optical depths provide a VHE-anchored determination of the local EBL intensity. The agreement with galaxy counts and deep-space measurements indicates that known galaxy populations account for most of the optical and near-IR background, leaving limited room for an additional diffuse component.

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