Evidence against star-forming galaxies as the dominant source of IceCube neutrinos

Nov 2, 2015
9 pages
Published in:
  • Astrophys.J. 836 (2017) 1, 47
  • Published: Feb 7, 2017
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Abstract: (IOP)
The cumulative emission resulting from hadronic cosmic-ray interactions in star-forming galaxies (SFGs) has been proposed as the dominant contribution to the astrophysical neutrino flux at TeV to PeV energies reported by IceCube. The same particle interactions also inevitably create γ-ray emission that could be detectable as a component of the extragalactic γ-ray background (EGB), which is now measured with the Fermi-LAT in the energy range from 0.1 to 820 GeV. New studies of the blazar flux distribution at γ-ray energies above 50 GeV place an upper bound on the residual non-blazar component of the EGB. We show that these results are in strong tension with models that consider SFGs as the dominant source of the diffuse neutrino backgrounds. A characteristic spectral index for parent cosmic rays in starburst galaxies of Γ(SB) ≃ 2.3 for dN/dEEΓSB{dN}/{dE}\propto {E}^{-{{\rm{\Gamma }}}_{\mathrm{SB}}} is consistent with the observed scaling relation between γ-ray and IR luminosity for SFGs, the bounds from the non-blazar EGB, and the observed γ-ray spectra of individual starbursts, but underpredicts the IceCube data by approximately an order of magnitude.
Note:
  • 10 pages, 6 figures, 1 table, published in ApJ
  • galaxies: starburst
  • gamma rays: diffuse background
  • neutrinos
  • gamma ray: energy
  • gamma ray: background
  • neutrino: background
  • neutrino: UHE
  • neutrino: spectrum
  • galaxy
  • accelerator