Tomographic Constraints on High-Energy Neutrinos of Hadronuclear Origin

TL;DR

This study uses tomographic analysis of gamma-ray and galaxy data to constrain the origins of high-energy neutrinos, ruling out certain source classes and supporting starburst galaxies as potential sources.

Contribution

It introduces a novel tomographic approach to constrain neutrino sources by cross-correlating gamma-ray and galaxy distributions, providing tighter bounds than previous spectral methods.

Findings

Excludes hadronuclear sources with spectra softer than E^{-2.1} under certain evolution assumptions.

Finds starburst galaxies are consistent with spectral and tomographic constraints.

Provides tighter bounds on neutrino luminosity density than gamma-ray background spectrum analysis.

Abstract

Mounting evidence suggests that the TeV-PeV neutrino flux detected by the IceCube telescope has mainly an extragalactic origin. If such neutrinos are primarily produced by a single class of astrophysical sources via hadronuclear ($pp$) interactions, a similar flux of gamma-ray photons is expected. For the first time, we employ tomographic constraints to pinpoint the origin of the IceCube neutrino events by analyzing recent measurements of the cross correlation between the distribution of GeV gamma rays, detected by the Fermi satellite, and several galaxy catalogs in different redshift ranges. We find that the corresponding bounds on the neutrino luminosity density are up to one order of magnitude tighter than those obtained by using only the spectrum of the gamma-ray background, especially for sources with mild redshift evolution. In particular, our method excludes any hadronuclear source with a spectrum softer than $E^{-2.1}$ as a main component of the neutrino background, if its evolution is slower than $(1+z)^3$. Starburst galaxies, if able to accelerate and confine cosmic rays efficiently, satisfy both spectral and tomographic constraints.