Chemical abundance of LINER galaxies -- Metallicity calibrations based on SDSS-IV MaNGA

TL;DR

This study develops new empirical calibrations to estimate the metallicity of LINER galaxies using SDSS-IV MaNGA data, based on photoionization models and emission-line ratios, addressing the uncertain ionizing sources.

Contribution

First to propose semi-empirical oxygen abundance calibrations for LINERs based on photoionization models and observational data.

Findings

Oxygen abundance range in LINERs: 8.48 to 8.84.

N2 index provides more precise metallicity estimates than O3N2.

Metallicity estimates agree with extrapolated disk gradients.

Abstract

The ionizing source of Low Ionization Nuclear Emission Regions (LINERs) is uncertain. Because of this, an empirical relation to determine the chemical abundances of these objects has not been proposed. In this work, for the first time, we derived two semi-empirical calibrations based on photoionization models to estimate the oxygen abundance of LINERS as a function of the $N2$ and $O3N2$ emission-line intensity ratios. These relations were calibrated using oxygen abundance estimations obtained by comparing the observational emission-line ratios of 43 LINER galaxies (taken from the MaNGA survey) and grids of photoionization models built with the {\sc Cloudy} code assuming post-Asymptotic Giant Branch (post-AGB) stars with different temperatures. We found that the oxygen abundance of LINERs in our sample is in the $\rm 8.48 <~ 12+log(O/H) <~ 8.84$ range, with a mean value of $\rm 12+\log(O/H)=8.65$. We recommend the use of the $N2$ index to estimate the oxygen abundances of LINERs, since the calibration with this index presented a much smaller dispersion than the $O3N2$ index. In addition, the estimated metallicities are in good agreement with those derived by extrapolating the disk oxygen abundance gradients to the centre of the galaxies showing that the assumptions of the models are suitable for LINERs. We also obtained a calibration between the logarithm of the ionization parameter and the [OIII]/[OII] emission-line ratio.