2021MNRAS.508..371A

For the first time, neon abundance has been derived in the narrow line region from a sample of Seyfert 2 nuclei. In view of this, we compiled from the literature fluxes of optical and infrared (IR) narrow emission lines for 35 Seyfert 2 nuclei in the local universe (z \:≲\:0.06). The relative intensities of emission lines were used to derive the ionic and total neon and oxygen abundances through electron temperature estimations (T_e-method). For the neon, abundance estimates were obtained by using both T_e-method and IR-method. Based on photoionization model results, we found a lower electron temperature [t_e(Ne III)] for the gas phase where the Ne^2 +^ is located in comparison with t₃ for the O^2 +^ ion. We find that the differences (D) between Ne^2 +^/H+^ ionic abundances calculated from IR-method and T_e-method (assuming t₃ in the Ne^2 +^/H+^ derivation) are similar to the derivations in star-forming regions (SFs) and they are reduced by a mean factor of ∼3 when t_e( Ne III) is considered. We propose a semi-empirical Ionization Correction Factor (ICF) for the neon, based on [Ne II]12.81µm, [Ne III]15.56µm, and oxygen ionic abundance ratios. We find that the average Ne/H abundance for the Seyfert 2s sample is nearly 2 times higher than similar estimate for SFs. Finally, for the very high metallicity regime (i.e. [ 12+log(O/H)\: ≳\: 8.80]) an increase in Ne/O with O/H is found, which likely indicates secondary stellar production for the neon.