Components of the Extragalactic Gamma Ray Background

TL;DR

This paper estimates the contributions of unresolved blazars and star-forming galaxies to the extragalactic gamma-ray background, discussing constraints on other potential sources like dark matter and diffuse emission.

Contribution

It provides new theoretical estimates of the relative contributions of unresolved sources to the EGB and analyzes their compatibility with observational data.

Findings

Unresolved blazars could dominate the EGB according to Fermi data.

Unresolved star-forming galaxies may significantly contribute within uncertainties.

Star-forming galaxies cannot explain the EGB spectrum at 50-200 MeV.

Abstract

We present new theoretical estimates of the relative contributions of unresolved blazars and star-forming galaxies to the extragalactic gamma-ray background (EGB) and discuss constraints on the contributions from alternative mechanisms such as dark matter annihilation and truly diffuse gamma-ray production. We find that the Fermi source count data do not rule out a scenario in which the EGB is dominated by emission from unresolved blazars, though unresolved star-forming galaxies may also contribute significantly to the background, within order-of-magnitude uncertainties. In addition, we find that the spectrum of the unresolved star-forming galaxy contribution cannot explain the EGB spectrum found by EGRET at energies between 50 and 200 MeV, whereas the spectrum of unresolved FSRQs, when accounting for the energy-dependent effects of source confusion, could be consistent with the combined spectrum of the low-energy EGRET EGB measurements and the Fermi-LAT EGB measurements.