Updated Fermi-LAT Constraints on the Extragalactic Background Light
2017 December 12
The extragalactic background light (EBL) is a fundamental cosmological observable of our universe, allowing insight into the history of star formation within our universe. Extending between 0.1 - 1000 $\mu$m, it is the UV to near-IR that is of interest in high and very high energy astronomy, where EBL photons interact via pair production to leave a visible imprint in the spectra of distant AGN. Multiple studies have been carried out using ground-based Cherenkov telescopes, which can observe the spectra of relatively nearby AGN to provide limits on the density of the EBL. These however do not reveal a great amount of detail concerning the evolution of the EBL with time, and therefore the star formation rate. The Fermi-LAT instrument, with its long exposure of the extragalactic sky, holds an extensive sample of AGN extending out to large redshifts (z < 2.56) and has been used by the Fermi-LAT collaboration to study the EBL. Here we further that study by combining a sample of 259 AGN, carefully modelling their spectral energy distributions and determine a redshift-dependent EBL correction factors to a range of models, taking into account the temporal and spectral variability of sources.