The Imprint of The Extragalactic Background Light in the Gamma-Ray Spectra of Blazars

TL;DR

This paper detects an absorption feature in gamma-ray spectra of blazars caused by the extragalactic background light, enabling measurement of the EBL flux density and shedding light on cosmic star formation and galaxy evolution.

Contribution

It presents the first measurement of the EBL flux density using gamma-ray absorption features in blazar spectra, providing new insights into the EBL's intensity and its role in cosmic history.

Findings

Detected absorption feature in gamma-ray spectra of blazars.

Measured EBL flux density in optical to UV frequencies.

Confirmed EBL's impact on gamma-ray attenuation at high redshift.

Abstract

The light emitted by stars and accreting compact objects through the history of the Universe is encoded in the intensity of the extragalactic background light (EBL). Knowledge of the EBL is important to understand the nature of star formation and galaxy evolution, but direct measurements of the EBL are lim- ited by Galactic and other foreground emissions. Here we report an absorption feature seen in the combined spectra of a sample of gamma-ray blazars out to a redshift of z$\sim$1.6. This feature is caused by attenuation of gamma rays by the EBL at optical to UV frequencies, and allowed us to measure the EBL flux density in this frequency band.