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

TY - JOUR

T1 - Evidence against star-forming galaxies as the dominant source of IceCube neutrinos

AU - Bechtol, K.

AU - Ahlers, Markus Tobias

AU - Di Mauro, M

AU - Ajello, M.

AU - Vandenbroucke, J.P.

PY - 2017/2/10

Y1 - 2017/2/10

N2 - 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 ΓSB ≃ 2.3 for is dN/dE ∝ E-ΓSB 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.

AB - 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 ΓSB ≃ 2.3 for is dN/dE ∝ E-ΓSB 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.

U2 - 10.3847/1538-4357/836/1/47

DO - 10.3847/1538-4357/836/1/47

M3 - Journal article

SN - 0004-637X

VL - 836

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 1

M1 - 47

ER -