Decaying neutrinos as a photoionization source in galactic halos

We propose that the highly ionized carbon (CIV) and silicon (Si IV) observed by the International Ultraviolet Explorer several kiloparsecs from the plane of the Galaxy result from a flux of ∼50-eV photons. If neutrinos of rest mass $m_{\nu }\sim 100$ eV exist and dominate the galactic halo, their decay into 50-eV photons may produce the observed ionization. The observations then require a decay time $\tau \sim {10}^{27}$ sec, which exceeds established lower limits by ${10}^3$, and is in line with model-dependent estimates for 100-eV neutrinos based on theoretical considerations from elementary-particle physics which avoid Glashow-Iliopoulos-Maiani suppressions (e.g., by invoking a very massive fourth neutrino type).