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We investigate the discrepancy between oxygen abundance estimations fornarrow-line regions (NLRs) of Active Galactic Nuclei (AGNs) type Seyfert 2derived by using direct estimations of the electron temperature (Te-method) andthose derived by using photoionization models. In view of this, observationalemission-line ratios in the optical range (3000 < \lambda(\AA) < 7000) ofSeyfert 2 nuclei compiled from the literature were reproduced by detailedphotoionization models built with the Cloudy code. We find that the deriveddiscrepancies are mainly due to the inappropriate use of the relations betweentemperatures of the low (t2) and high (t3) ionization gas zones derived for HII regions in AGN chemical abundance studies. Using a photoionization modelgrid, we derived a new expression for t2 as a function of t3 valid for Seyfert2 nuclei. The use of this new expression in the AGN estimation of the O/Habundances based on Te-method produces O/H abundances slightly lower (about 0.2dex) than those derived from detailed photoionization models. We also find thatthe new formalism for the Te-method reduces by about 0.4 dex the O/Hdiscrepancies between the abundances obtained from strong emission-linecalibrations and those derived from direct estimations.

Chemical abundances of Seyfert 2 AGNs-III. Reducing the oxygen abundance discrepancy