Normal O Stars in Dense Media Generate LINERs

Low-ionization nuclear emission-line regions (LINERS) are often regarded as low-luminosity extensions of quasar and Seyfert phenomena that may be powered by accretion onto a massive black hole. New calculations are presented that show that the general characteristics of LINERS can be generated via photoionization by relatively hot yet normal main-sequence: O stars (~O5 or earlier). The calculation results show improved agreement with observed LINER properties if the irradiated plasma is relatively dense and characterized by solar abundances modified by normal grain depletion. Unusually dense circumstellar media may be a natural consequence of high interstellar pressures, which may explain the preference of LINER phenomena for the nuclei of large and early-type galaxies.