The Galactic Plane Share of the Diffuse Neutrino Flux and Its Energy Dependence

In 2023 the IceCube collaboration reported neutrino emission from the Galactic plane, the first detection of our own Galaxy in this messenger. This paper places that component inside the total diffuse budget and computes how its share changes with energy. Taking the Galactic fraction at 100 TeV as 9 per cent, within the published template range of 6 to 13 per cent, the Galactic E-squared flux per flavour is 2.250e-09 against an extragalactic remainder of 2.275e-08. If the Galactic spectrum, with index 2.6, is slightly softer than the extragalactic index 2.5, the Galactic share rises to 11.1 per cent at 10 TeV and falls to 7.28 per cent at 1 PeV. The Galaxy is a minority contributor at every energy, largest where atmospheric backgrounds are worst — a combination that explains both why the detection took a decade and why it matters for the lowest-energy diffuse analyses. The study is computed from stated assumptions, not measured.