Abundance estimations in the NLRs of Type 2 AGNs

Abstract

Chemical abundances of the Narrow Line Regions (NLRs) of Active Galactic Nuclei (AGNs) are still poorly estimated. It is not clear that the methods developed for the study of the gas phase in HII regions are valid and/or provide accurate/realistic estimations of the NLRs abundances. Here we present a brief summary of the work carried out by our group on the study of chemical abundances of the NLRs associated to type 2 AGNs. We used different grids of photoionization models built using the Cloudy code. We derived new indexes to estimate the oxygen abundances of the NLRs using ultra violet and optical emission lines combined with the grids of photoionization models. We also obtained new quantitative determinations of the nitrogen abundance and a consistent relation between the nitrogen and oxygen abundances for a sample of nearby Seyfert 2 galaxies, located at redshift z < 0.1. Our results for N/O vs. O/H abundance ratios derived for Seyfert 2 galaxies are in consonance with those derived for a sample of extragalactic disc HII regions with high metallicity.