The diffuse $\gamma$-ray background is dominated by star-forming galaxies

Abstract

The Fermi Gamma-ray Space Telescope has revealed a diffuse $\gamma$-ray background at energies from 0.1 GeV to 1 TeV, which can be separated into Galactic emission and an isotropic, extragalactic component. Previous efforts to understand the latter have been hampered by the lack of physical models capable of predicting the $\gamma$-ray emission produced by the many candidate sources, primarily active galactic nuclei and star-forming galaxies, leaving their contributions poorly constrained. Here we present a calculation of the contribution of star-forming galaxies to the $\gamma$-ray background that does not rely on empirical scalings, and is instead based on a physical model for the $\gamma$-ray emission produced when cosmic rays accelerated in supernova remnants interact with the interstellar medium. After validating the model against local observations, we apply it to the observed cosmological star-forming galaxy population and recover an excellent match to both the total intensity and the spectral slope of the $\gamma$-ray background, demonstrating that star-forming galaxies alone can explain the full diffuse, isotropic $\gamma$-ray background.

18 pages, 10 figures. This work has been published in Nature. The version deposited here is the author's pre-print and may not reflect post-acceptance corrections or formatting related changes. The published version (Version of Record) of this manuscript is available at https://www.nature.com/articles/s41586-021-03802-x

References in corpus (18)

• Cosmic Star Formation History
• 3D-HST+CANDELS: The Evolution of the Galaxy Size-Mass Distribution since $z=3$
• The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV
• Parametrization of gamma-ray production cross-sections for pp interactions in a broad proton energy range from the kinematic threshold to PeV energies
• The Origin of the Extragalactic Gamma-Ray Background and Implications for Dark-Matter Annihilation
• The extragalactic background light revisited and the cosmic photon-photon opacity
• X-ray coronae in simulations of disc galaxy formation
• Cosmic Gamma-Ray Background from Star-Forming Galaxies
• Cosmic ray transport in starburst galaxies
• Joint anisotropy and source count constraints on the contribution of blazars to the diffuse gamma-ray background
• Tomography of the Fermi-LAT gamma-ray diffuse extragalactic signal via cross-correlations with galaxy catalogs
• ALMA observations of 99 GHz free-free and H40$\alpha$ line emission from star formation in the centre of NGC 253
• Free-free and H42alpha emission from the dusty starburst within NGC 4945 as observed by ALMA
• What drives the velocity dispersion of ionized gas in star-forming galaxies?
• Gravitational Instability in Radiation Pressure Dominated Backgrounds
• The gamma-ray / infrared luminosity correlation of star-forming galaxies
• Non-linear weak lensing forecasts
• Optical spectroscopy of Arp220: the star formation history of the closest ULIRG

Cited by in corpus (3)

• The extragalactic $\gamma$-ray background: imprints from the physical properties and evolution of star-forming galaxy populations
• Multimessenger Astronomy with Neutrinos
• Classification of Fermi-LAT blazars with Bayesian neural networks