Chemical abundances in spiral and irregular galaxies. O and N abundances derived from global emission--line spectra

TL;DR

This study validates the use of global emission-line spectra to accurately determine oxygen and nitrogen abundances in galaxies, confirming previous findings and applying the method to various galaxy samples including UV-selected and intermediate-redshift galaxies.

Contribution

It demonstrates that global spectra can reliably estimate galaxy chemical abundances and distinguishes high and low metallicity galaxies, extending the method to diverse galaxy types and redshifts.

Findings

Global spectra reliably indicate galaxy chemical properties.

UV-selected galaxies follow the same N/O -- O/H relation as local HII regions.

Intermediate-redshift galaxies deviate from local metallicity-luminosity trends.

Abstract

The validity of oxygen and nitrogen abundances derived from the global emission-line spectra of galaxies via the P-method has been investigated using a collection of published spectra of individual HII regions in irregular and spiral galaxies. The conclusions of Kobulnicky, Kennicutt & Pizagno (1999) that global emission-line spectra can reliably indicate the chemical properties of galaxies has been confirmed. It has been shown that the comparison of the global spectrum of a galaxy with a collection of spectra of individual HII regions can be used to distinguish high and low metallicity objects and to estimate accurate chemical abundances in a galaxy. The oxygen and nitrogen abundances in samples of UV-selected and normal nearby galaxies have been determined. It has been found that the UV-selected galaxies occupy the same area in the N/O -- O/H diagram as individual HII regions in nearby galaxies. Finally, we show that intermediate-redshift galaxies systematically deviate from the metallicity -- luminosity trend of local galaxies.