Cosmic Gamma-Ray Background from Star-Forming Galaxies

Abstract

The origin of the extragalactic gamma-ray background is a pressing cosmological mystery. The Fermi Gamma-Ray Space Telescope has recently measured the intensity and spectrum of this background; both are substantially different from previous measurements. We present a novel calculation of the gamma-ray background from normal star-forming galaxies. Contrary to long-standing expectations, we find that numerous but individually faint normal galaxies may comprise the bulk of the Fermi signal, rather than rare but intrinsically bright active galaxies. This result has wide-ranging implications, including: the possibility to probe the cosmic star formation history with gamma rays; the ability to infer the cosmological evolution of cosmic rays and galactic magnetic fields; and an increased likelihood of identifying subdominant components from rare sources (e.g., dark matter clumps) through their large anisotropy.

5 pages, 1 figure. Matches version published in ApJL. Sharper focus on normal (vs starburst) galaxies. Basic conclusions unchanged

References in corpus (11)

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Cited by in corpus (7)

• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Joint anisotropy and source count constraints on the contribution of blazars to the diffuse gamma-ray background
• Gamma-Ray and Neutrino Backgrounds as Probes of the High-Energy Universe: Hints of Cascades, General Constraints, and Implications for TeV Searches
• Contribution from Star-Forming Galaxies to the Cosmic Gamma-Ray Background Radiation
• The cosmic X-ray and gamma-ray background from dark matter annihilation
• Diffuse gamma-ray constraints on dark matter revisited. I: the impact of subhalos
• Probing the coupling of heavy dark matter to nucleons by detecting neutrino signature from the Earth's core