Semi-empirical calibration of the oxygen abundance for LINER galaxies based on SDSS-IV MaNGA -- The case for strong and weak AGN

TL;DR

This study develops a semi-empirical calibration linking oxygen abundance to emission-line ratios in LINER galaxies, distinguishing between weak and strong AGN, and compares results across different samples.

Contribution

It introduces a new calibration method for oxygen abundance in LINERs based on SDSS-IV MaNGA data and photoionization models, differentiating weak and strong AGN.

Findings

Weak AGN LINERs have oxygen abundances around 8.68 on average.

Strong AGN LINERs have oxygen abundances around 8.65 on average.

LINER oxygen abundances do not correlate clearly with host galaxy stellar mass.

Abstract

In this paper, we present a semi-empirical calibration between the oxygen abundance and the $N2$ emission-line ratio for Low Ionization Nuclear Emission Regions (LINERs). This relation was derived by comparing the optical spectroscopic data of 118 nuclear spaxels classified as LINERs using three different BPT diagrams from the Mapping Nearby Galaxies survey (MaNGA) and sub-classified as weak (wAGN, 84 objects) and strong (sAGN, 34 objects) AGN (active galactic nucleus) from the WHAN diagnostic diagram and photoionization model results obtained with the {\sc cloudy} code assuming gas accretion into a black hole (representing an AGN). We found that our wAGN LINERs exhibit an oxygen abundance in the range of $8.50 \lesssim \mathrm{12+\log(O/H)} \lesssim 8.90 $, with an average value of $\mathrm{12+\log(O/H)}=8.68$, while our sAGN LINERs exhibit an oxygen abundance in the range of $8.51 \lesssim \: \mathrm{12+\log(O/H)} \: \lesssim \: 8.81 $, with an average value of $\mathrm{12+\log(O/H)}=8.65$. Our abundance estimations are in good agreement with those derived for another two different samples one of them with 463 Seyfert 2 objects and the other with 43 LINERs galaxies ionized by post-AGB stars, showing that the assumptions of our models are likely suitable for wAGN and sAGN LINERs. A relation between the equivalent width of the observed H$\alpha$ emission-line and the estimated ionization parameter provided by models was obtained. Our results also suggest that LINERs does not show a clear correlation between oxygen abundances and the stellar mass of the hosting galaxies.