A New Measurement of the Extragalactic Background Light using 15\,yr of {\it Fermi}-Large Area Telescope Data

TL;DR

This paper presents a highly precise measurement of the extragalactic background light (EBL) using 15 years of Fermi-LAT gamma-ray data, enhancing understanding of cosmic star formation and galaxy evolution.

Contribution

It provides the most accurate EBL measurement to date by analyzing gamma-ray attenuation in a large sample of blazars over an extended redshift range.

Findings

Detected EBL attenuation with ~23σ significance.

Measured EBL optical depth across 19 redshift bins.

Reconstructed EBL evolution consistent with recent models.

Abstract

The extragalactic background Light (EBL) from ultraviolet to infrared comprises the emission from all stars, galaxies, and actively accreting black holes in the observable Universe. A precise measurement of the EBL is critically important to probe models of star formation and galaxy evolution. The EBL can be measured via the absorption imprint left on the spectra of gamma-ray blazars. In this work, we rely on 15 years of {\it Fermi}-LAT data and 1576 blazars to measure the EBL optical depth in the $0<z<4.3$ range. We detect the EBL attenuation with $\sim23\sigma$ significance and measure the optical depth in 19 redshift bins, extending the coverage and improving on our previous results. This allows us to reconstruct the EBL evolution and find general consistency with recent EBL models. These results represent the most precise determination of the EBL with GeV $\gamma$ rays to date.