Extragalactic Gamma-ray Background Radiation from Beamed and Unbeamed Active Galactic Nuclei

TL;DR

This paper estimates the contributions of different active galactic nuclei populations, including blazars and radio galaxies, to the extragalactic gamma-ray background, revealing that radio galaxies account for about 25% of the unresolved EGRB.

Contribution

It introduces a new estimate of gamma-ray loud radio galaxies' contribution to the EGRB using radio luminosity functions and luminosity correlations, expanding understanding beyond blazars.

Findings

Blazars explain ~22% of unresolved EGRB.

Radio galaxies contribute ~25% to unresolved EGRB.

Combined, AGN populations account for a significant portion of EGRB.

Abstract

The origin of the extragalactic gamma-ray background (EGRB) radiation has been a mystery in astrophysics for a long time. Recently the Fermi gamma-ray satellite (Fermi) has revealed that ~22% of the unresolved EGRB would be explained by blazars, which are one population of beamed active galactic nuclei (AGNs). The remaining ~78% of the unresolved EGRB is still unknown. We estimate the contribution of gamma-ray loud radio galaxies, which are misaligned radio loud AGNs recently detected by Fermi, to EGRB using the radio luminosity function of radio-loud AGNs with the correlation between the radio and gamma-ray luminosities. We find that ~25% of the unresolved EGRB will be explained by gamma-ray loud radio galaxy population. We also discuss further about the origin of EGRB by comparing the Fermi EGRB data with our studies on various AGN populations' contribution to EGRB, which are radio quiet AGNs, blazars, and gamma-ray loud radio galaxies.