Composition of the Fermi-LAT isotropic gamma-ray background intensity: Emission from extragalactic point sources and dark matter annihilations

TL;DR

This paper analyzes the isotropic gamma-ray background observed by Fermi-LAT, attributing it to extragalactic sources and dark matter annihilations, and sets limits on dark matter properties based on the data.

Contribution

It provides a new estimation of the IGRB, models its sources including active galactic nuclei, star-forming galaxies, and dark matter, and explores dark matter parameter space.

Findings

Good fit of IGRB with AGN and star-forming galaxy models

Stringent limits on dark matter annihilation cross section

Identification of dark matter parameters that improve fit

Abstract

A new estimation of the isotropic diffuse gamma-ray background (IGRB) observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi) has been presented for 50 months of data, in the energy range 100 MeV-820 GeV and for different modelings of the Galactic foreground. We attempt here the interpretation of the Fermi-LAT IGRB data in terms of the gamma-ray unresolved emission from different extragalactic populations. We find very good fits to the experimental IGRB, obtained with theoretical predictions for the emission from active galactic nuclei and star-forming galaxies. In addition, we probe a possible emission coming from the annihilation of weakly interacting dark matter (DM) particles in the halo of our Galaxy. We set stringent limits on its annihilation cross section into gamma rays, which are about the thermal relic value for a wide range of DM masses. We also identify regions in the DM mass and annihilation cross section parameter space which can significantly improve the fit to the IGRB data. Our analysis is conducted within the different IGRB data sets obtained from different models for the Galactic emission, which is shown to add a significant ambiguity on the IGRB interpretation.