Milky Way as a Neutrino Desert Revealed by IceCube Galactic Plane Observation

TL;DR

This paper analyzes high-energy neutrino and gamma-ray data from the Galactic plane, revealing that the Milky Way's neutrino emission is significantly lower than that of distant galaxies, suggesting it is a neutrino desert.

Contribution

It demonstrates that the Milky Way's neutrino luminosity is much lower than extragalactic sources, indicating a lack of dominant neutrino emitters in our galaxy in recent times.

Findings

Neutrino flux from the Milky Way is 1-2 orders of magnitude lower than distant galaxies.

Gamma-ray observations are consistent with hadronuclear interactions above 1 TeV.

Our galaxy has not hosted dominant neutrino sources in the recent tens of kiloyears.

Abstract

The Galactic diffuse emission (GDE) is formed when cosmic rays leave the sources where they were accelerated, diffusively propagate in the Galactic magnetic field, and interact with the interstellar medium and interstellar radiation field. GDE in $\gamma$-ray (GDE-$\gamma$) has been observed up to sub-PeV energies, though its origin may be explained by either cosmic-ray nuclei or electrons. We show that the $\gamma$-rays accompanying the high-energy neutrinos recently observed by the IceCube Observatory from the Galactic plane have a flux that is consistent with the GDE-$\gamma$ observed by the {\it Fermi}-LAT and Tibet AS$\gamma$ experiments around 1 TeV and 0.5 PeV, respectively. The consistency suggests that the diffuse $\gamma$-ray emission above $\sim$1TeV could be dominated by hadronuclear interactions, though partial leptonic contribution cannot be excluded. Moreover, by comparing the fluxes of the Galactic and extragalactic diffuse emission backgrounds, we find that the neutrino luminosity of the Milky Way is one to two orders of magnitude lower than the average of distant galaxies. This implies that our Galaxy has not hosted the type of neutrino emitters that dominates the isotropic neutrino background at least in the past few tens of kiloyears.