NeIII/OII as an oxygen abundance indicator in the HII regions and HII galaxies

TL;DR

This study calibrates the Ne3O2 emission line ratio as a reliable, reddening-insensitive indicator of oxygen abundance in HII regions and galaxies, covering a broad metallicity range.

Contribution

It provides a new linear calibration of Ne3O2 as an oxygen abundance indicator based on a large SDSS sample, extending its applicability across a wide metallicity range.

Findings

Ne3O2 correlates linearly with oxygen abundance from 7.0 to 9.0.

Ne3O2 is unaffected by internal reddening, making it useful for high-redshift studies.

Dispersion in metal-rich galaxies partly due to oxygen depletion onto grains.

Abstract

To calibrate the relationship between Ne3O2 (Ne3O2 = log(\neiii$\lambda3869$/\oii$\lambda3727$)) and oxygen abundances, we present a sample of $\sim$3000 $\hii$ galaxies from the Sloan Digital Sky Survey (SDSS) data release four. They are associated with a sample from the literature intended to enlarge the oxygen abundance region. We calculated the electron temperatures ($T_e$) of 210 galaxies in the SDSS sample with the direct method, and $T_e$ of the other 2960 galaxies in SDSS sample calculated with an empirical method. Then, we use a linear least-square fitting to calibrate the Ne3O2 oxygen abundance indicator. It is found that the Ne3O2 estimator follows a linear relation with \zoh\ that holds for the whole abundance range covered by the sample, from approximately 7.0 to 9.0. The best linear relationship between the Ne3O2 and the oxygen abundance is calibrated. The dispersion between oxygen abundance and Ne3O2 index in the metal rich galaxies may come partly from the moderate depletion of oxygen onto grains. The $Ne3O2$ method has the virtue of being single-valued and not affected by internal reddening. As a result, the $Ne3O2$ method can be a good metallicity indicator in the \hii regions and \hii galaxies, especially in high-redshift galaxies.