Astrophysical Sources of High-Energy Neutrinos in the IceCube Era

High-energy neutrino astrophysics has come of age with IceCube's discovery of neutrinos in the TeV to PeV energy range, attributable to extragalactic sources at cosmological distances. At such energies, astrophysical neutrinos must originate in cosmic-ray interactions, providing information about the sources of high-energy cosmic rays, as well as leading to the coproduction of high-energy γ-rays. The intimate link with these two independently observed types of radiation provides important tools for the quest to identify and understand the nature of the astrophysical sources of the neutrinos. These neutrinos can set important constraints on the cosmic-ray acceleration process, and because they travel essentially unimpeded, they can probe our Universe out to the farthest cosmological distances.