Speaker
Description
The extragalactic background light (EBL) is a key observable for understanding galaxy evolution and cosmology, as it represents the cumulative radiation from all star-forming galaxies throughout cosmic history, spanning ultraviolet to far-infrared wavelengths, with an additional, less certain contribution from active galactic nuclei. High-energy gamma rays from distant blazars interact with the EBL via pair production, leading to an energy-dependent attenuation measurable with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. We present an updated measurement of the evolving EBL using the first 15 years of Fermi-LAT data, analyzing a sample of approximately 1500 blazars from the 4LAC catalog, reaching z ~ 4 and effectively doubling the source count from previous studies. Compared to the 12 redshift bins in our previous analysis based on 9 years of data, we now resolve EBL attenuation across 19 redshift bins with reduced uncertainties, refining our ability to trace its evolution back to a Universe age of only 1.5 billion years. These results enables us to probe the cosmic gamma-ray horizon, i.e. the energy at which the universe becomes opaque to gamma rays, and the EBL evolution with unprecedented accuracy. These findings provide the most detailed characterization of the EBL ever achieved with Fermi-LAT.
| Collaboration(s) | Fermi-LAT |
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