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

Keith Bechtol; Markus Ahlers; Mattia Di Mauro; Marco Ajello; Justin Vandenbroucke

doi:10.3847/1538-4357/836/1/47

paper

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

arXiv:1511.00688 · doi:10.3847/1538-4357/836/1/47

Abstract

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 $d N / d E \propto E^{- Γ_{SB}}$ 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.

10 pages, 6 figures, 1 table, published in ApJ

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

Abstract

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