Temperature discrepancy with narrow line region photoionization models

Using published work on the Narrow Line Region of Active Nuclei, we make a comparison of the observed [O iii] 4363Å/5007Å ratio observed among quasars, Seyfert 2’s and spatially resolved NLR plasma. It is broadly accepted that the span of this ratio among quasars, from 0.015 to ≃ 0.2, is the result of collisional deexcitation as corroborated by Baskin and Laor (2005). However, the coincidence of the AGN at towards the lowest [O iii] ratios, however, suggests that it represents plasma in the low density regime, where this ratio can be interpreted as the actual NLR temperature. Using the density indicator [Ar iv] λ4711Å/λ4740Å doublet ratio which was observed by Koski (1978) in Seyfert 2’s, we found evidence of relatively low densities ( ∼ < 10 cm). Even after considering a powerlaw distribution for the densities as well as a non-uniform foreground dust extinction, we find no evidence of collisional deexcitation. The mean NLR 〈TOIII〉 temperature we infer for our Seyfert sample is 13 500 °K. This is a problem for photoionization models with a standard ionizing spectral energy distribution since they derive significantly lower temperatures.