Speaker
Description
The extragalactic background light (EBL) encodes the integrated emission history of all extragalactic sources and serves as a key probe of star formation and galaxy evolution. Gamma-ray observations offer a unique method to measure the EBL through the energy-dependent attenuation of blazar spectra via pair production with EBL photons. We present complementary EBL measurements spanning GeV to TeV energies. Using 15 years of Fermi-LAT data and 1576 blazars, we detect EBL attenuation at ~23 sigma significance and measure the optical depth across 19 redshift bins out to z ~ 4.3, providing the most precise GeV determination of the EBL to date. At very high energies, we analyze 268 spectra from 45 sources observed with Imaging Atmospheric Cherenkov Telescopes, finding that seven EBL templates require only ≤10% rescaling to match the observed attenuation. Combining GeV and TeV optical depths, we reconstruct the local EBL intensity at z = 0 using both empirical and physically motivated models. The reconstructions agree with integrated galaxy counts to within 2-3 nW m⁻² sr⁻¹ over 0.5-30 μm, while the near-IR excess reported by IRTS and CIBER is disfavored at 3-5 sigma. These results indicate that known galaxy populations account for most of the optical-to-near-IR background.
