Observation of neutrinos from the Milky Way Galaxy

Visible in the sky as a swath of stars, dust, and gas, the Milky Way Galaxy has been studied from Earth for millennia. More recently, the Galactic plane of the Milky Way has been observed in every wavelength of the electromagnetic spectrum, from radio waves to infrared, optical, x-rays, and gamma rays. This thesis presents the first observation of the Galactic plane in high-energy neutrinos, marking the first observation in a particle other than light. Within our Galaxy, high-energy neutrinos can be produced when cosmic rays interact at their acceleration sites and during propagation through the interstellar medium. Using a new sample of neutrinos with energies ranging from 500 GeV to multi-PeV, a test of a diffuse neutrino emission model from the Galactic plane finds a 4.5[sigma] rejection of the background-only hypothesis. This observation was enabled by machine-learning techniques that improved the selection efficiency and angular resolution of cascade-like neutrino events in IceCube.