New metallicity calibration for Seyfert 2 galaxies based on the N2O2
  index
  We derive a new relation between the metallicity of Seyfert 2 Active Galactic
Nuclei (AGNs) and the intensity of the narrow emission-lines ratio
$N2O2$=log([N II]$\lambda$6584/[O II]$\lambda$3727). The calibration of this
relation was performed determining the metallicity ($Z$) of a sample of 58 AGNs
through a diagram containing the observational data and the results of a grid
of photoionization models obtained with the Cloudy code. We find the new
$Z/Z_\odot$-$N2O2$ relation using the obtained metallicity values and the
corresponding observational emission line intensities for each object of the
sample. Estimations derived through the use of this new calibration indicate
that narrow line regions of Seyfert 2 galaxies exhibit a large range of
metallicities ($0.3 \: < \: Z/Z_{\odot} \: < \:2.0$), with a median value $Z
\approx Z_{\odot}$. Regarding the possible existence of correlations between
the luminosity $L(\rm H\beta$), the electron density, and the color excess
E(B$-$V) with the metallicity in this kind of objects, we do not find
correlations between them.
