Diffuse $\gamma$-ray emission from misaligned active galactic nuclei

TL;DR

This paper models the diffuse gamma-ray emission from misaligned active galactic nuclei (MAGN), showing they could account for up to nearly all of the isotropic gamma-ray background, with a significant theoretical uncertainty.

Contribution

It establishes a physical correlation between gamma-ray and radio-core luminosities for MAGN and constrains their gamma-ray luminosity function using Fermi-LAT data.

Findings

MAGN can contribute up to nearly 100% of the IGRB.

A correlation between gamma-ray and radio-core luminosities is demonstrated.

Theoretical flux uncertainty is nearly an order of magnitude.

Abstract

Active galactic nuclei (AGN) with jets seen at small viewing angles are the most luminous and abundant objects in the $\gamma$-ray sky. AGN with jets misaligned along the line-of-sight appear fainter in the sky, but are more numerous than the brighter blazars. We calculate the diffuse $\gamma$-ray emission due to the population of misaligned AGN (MAGN) unresolved by the Large Area Telescope (LAT) on the {\it Fermi} Gamma-ray Space Telescope ({\it Fermi}). A correlation between the $\gamma$-ray luminosity and the radio-core luminosity is established and demonstrated to be physical by statistical tests, as well as compatible with upper limits based on {\it Fermi}-LAT data for a large sample of radio-loud MAGN. We constrain the derived $\gamma$-ray luminosity function by means of the source count distribution of the radio galaxies (RGs) detected by the {\it Fermi}-LAT. We finally calculate the diffuse $\gamma$-ray flux due to the whole MAGN population. Our results demonstrate that the MAGN can contribute from 10% up to nearly the entire measured Isotropic Gamma-Ray Background (IGRB). We evaluate a theoretical uncertainty on the flux of almost an order of magnitude.