Precision abundance analysis of bright HII galaxies

TL;DR

This paper presents high-quality spectrophotometric data of seven luminous HII galaxies, applying a precise methodology to determine elemental abundances and ionization structures, thereby testing photo-ionization models used in abundance analysis.

Contribution

It introduces a methodology for accurate elemental abundance determination in HII galaxies using wide wavelength spectra and multiple electron temperature diagnostics.

Findings

Achieved 7% accuracy in oxygen abundance measurements.

Mapped nebular ionization structures using ionic ratios and emission lines.

Provided a means to test photo-ionization models with observational data.

Abstract

We present high signal-to-noise spectrophotometric observations of seven luminous HII galaxies. The observations have been made with the use of a double-arm spectrograph which provides spectra with a wide wavelength coverage, from 3400 to 10400\AA free of second order effects, of exactly the same region of a given galaxy. These observations are analysed applying a methodology designed to obtain accurate elemental abundances of oxygen, sulphur, nitrogen, neon, argon and iron in the ionized gas. Four electron temperatures and one electron density are derived from the observed forbidden line ratios using the five-level atom approximation. For our best objects errors of 1% in t_e([OIII]), 3% in t_e([OII]) and 5% in t_e([SIII]) are achieved with a resulting accuracy of 7% in total oxygen abundances, O/H. The ionisation structure of the nebulae can be mapped by the theoretical oxygen and sulphur ionic ratios, on the one side, and the corresponding observed emission line ratios, on the other -- the \eta and \eta' plots --. The combination of both is shown to provide a means to test photo-ionisation model sequences currently applied to derive elemental abundances in HII galaxies.