Star-forming galaxies as the origin of diffuse high-energy backgrounds: Gamma-ray and neutrino connections, and implications for starburst history

Apr 4, 2014
23 pages
Published in:
  • JCAP 09 (2014) 043
  • Published: Sep 25, 2014
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Abstract: (IOP)
Star-forming galaxies have been predicted to contribute considerably to the diffuse gamma-ray background as they are guaranteed reservoirs of cosmic rays. Assuming that the hadronic interactions responsible for high-energy gamma rays also produce high-energy neutrinos and that Script O(100) PeV cosmic rays can be produced and confined in starburst galaxies, we here discuss the possibility that star-forming galaxies are also the main sources of the high-energy neutrinos observed by the IceCube experiment. First, we compute the diffuse gamma-ray background from star-forming galaxies, adopting the latest Herschel PEP/HerMES luminosity function and relying on the correlation between the gamma-ray and infrared luminosities reported by Fermi observations. Then we derive the expected intensity of the diffuse high-energy neutrinos from star-forming galaxies including normal and starburst galaxies. Our results indicate that starbursts, including those with active galactic nuclei and galaxy mergers, could be the main sources of the high-energy neutrinos observed by the IceCube experiment. We find that assuming a cosmic-ray spectral index of 2.1–2.2 for all starburst-like galaxies, our predictions can be consistent with both the Fermi and IceCube data, but larger indices readily fail to explain the observed diffuse neutrino flux. Taking the starburst high-energy spectral index as free parameter, and extrapolating from GeV to PeV energies, we find that the spectra harder than E(-2.15) are likely to be excluded by the IceCube data, which can be more constraining than the Fermi data for this population.
Note:
  • 26 pages, including 7 figures. Discussion expanded, new figures added. Accepted by JCAP
  • gamma ray theory
  • gamma ray experiments
  • neutrino astronomy
  • galaxy surveys
  • gamma ray: background
  • gamma ray: emission
  • galaxy
  • cosmic radiation
  • neutrino
  • GLAST