Decomposing the Origin of TeV-PeV Emission from the Galactic Plane: Implications of Multi-messenger Observations

TL;DR

This paper analyzes the origins of high-energy neutrino and gamma-ray emissions from the Galactic plane, suggesting diffuse cosmic-ray interactions dominate the neutrino flux, with implications for multi-messenger astrophysics.

Contribution

It provides a comprehensive evaluation of the contributions of resolved sources and diffuse emission to the Galactic neutrino flux using multi-messenger data and catalogs.

Findings

IceCube neutrino flux exceeds resolved source contributions excluding leptonic sources.

Diffuse cosmic-ray interactions likely dominate the Galactic neutrino emission.

LHAASO diffuse gamma-ray emission may primarily originate from hadronic processes.

Abstract

High-energy neutrino and $\gamma$-ray emission has been observed from the Galactic plane, which may come from individual sources and/or diffuse cosmic rays. We evaluate the contribution of these two components through the multimessenger connection between neutrinos and $\gamma$ rays in hadronic interactions. We derive maximum fluxes of neutrino emission from the Galactic plane using $\gamma$-ray catalogs, including 4FGL, HGPS, 3HWC, and 1LHAASO, and measurements of the Galactic diffuse emission by Tibet AS$\gamma$ and LHAASO. We find that the IceCube Galactic neutrino flux is larger than the contribution from all resolved sources when excluding promising leptonic sources such as pulsars, pulsar wind nebulae, and TeV halos. Our result indicates that the Galactic neutrino emission is likely dominated by the diffuse emission by the cosmic-ray sea and unresolved hadronic $\gamma$-ray sources. In addition, the IceCube flux is comparable to the sum of the flux of non-pulsar sources and the LHAASO diffuse emission especially above 30 TeV. This implies that the LHAASO diffuse emission may dominantly originate from hadronic interactions, either as the truly diffuse emission or unresolved hadronic emitters. Future observations of neutrino telescopes and air-shower $\gamma$-ray experiments in the Southern hemisphere are needed to accurately disentangle the source and diffuse emission of the Milky Way.