Emission line activity in type 2 quasars from the Sloan Digital Sky Survey

Abstract

We have compared the optical emission line ratios of type 2 quasars from Zakamska et al. with standard AGN photoionization model predictions, Seyfert 2s, HII galaxies, and narrow line FRII radio galaxies. Moderate to high ionization narrow line radio galaxies and Seyfert 2s are indistinguishable from type 2 quasars based on their optical line ratios. The standard AGN photoionization models, widely discussed for other type 2 AGNs, can reproduce successfully the loci and trends of type 2 quasars in some of the main diagnostic diagrams. These models are not exempt of problems and the discrepancies with the data are the same encountered for other type 2 AGNs. As for these, realistic models must take into account a range of cloud properties, as widely demonstrated in the literature. We also study the possible impact of stellar photoionization.