CCAPP Seminar: Takahiro Sudoh (OSU Physics)

July 27, 2018
Tuesday, September 4, 2018 - 11:30am to 12:30pm
PRB 4138
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High-energy gamma-ray and neutrino production in star-forming galaxies across cosmic time

We present new theoretical modeling to predict the luminosity and spectrum of gamma-ray and neutrino emission of a star-forming galaxy, from the star formation rate, gas mass, stellar mass, and size, taking into account production, propagation, and interactions of cosmic rays. The model reproduces observed gamma-ray luminosities of nearby galaxies better than empirical power-law relations. This model is then used to predict the cosmic background flux of gamma-rays and neutrinos from star-forming galaxies, by using a semi-analytical model of cosmological galaxy formation. In our baseline model, star-forming galaxies produce about 20% of the isotropic gamma-ray background unresolved by Fermi, and only 0.5% of IceCube neutrinos. Even with an extreme model assuming a hard injection cosmic-ray spectral index of 2.0 for all galaxies, at most 22% of IceCube neutrinos can be accounted for. These results indicate that it is difficult to explain most of the IceCube neutrinos by star-forming galaxies, without violating the gamma-ray constraints from nearby galaxies.

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