Radio Galaxies Dominate the High-Energy Diffuse Gamma-Ray Background

TL;DR

Radio galaxies are the primary contributors to the diffuse gamma-ray background above 1 GeV, with new detections supporting their dominant role and potential link to high-energy neutrinos.

Contribution

This study provides the first significant gamma-ray detections of three specific radio galaxies and quantifies their dominant contribution to the gamma-ray background.

Findings

Radio galaxies produce approximately 77% of the diffuse gamma-ray background above 1 GeV.

First statistically significant gamma-ray detection of 3C 212, 3C 411, and B3 0309+411B.

Supports the hypothesis that radio galaxies are sources of high-energy astrophysical neutrinos.

Abstract

It has been suggested that unresolved radio galaxies and radio quasars (sometimes referred to as misaligned active galactic nuclei) could be responsible for a significant fraction of the observed diffuse gamma-ray background. In this study, we use the latest data from the Fermi Gamma-Ray Space Telescope to characterize the gamma-ray emission from a sample of 51 radio galaxies. In addition to those sources that had previously been detected using Fermi data, we report here the first statistically significant detection of gamma-ray emission from the radio galaxies 3C 212, 3C 411, and B3 0309+411B. Combining this information with the radio fluxes, radio luminosity function, and redshift distribution of this source class, we find that radio galaxies dominate the diffuse gamma-ray background, generating $77.2^{+25.4}_{-9.4}\%$ of this emission at energies above $\sim$1 GeV. We discuss the implications of this result and point out that it provides support for scenarios in which IceCube's high-energy astrophysical neutrinos also originate from the same population of radio galaxies.