Chemical abundances in spiral and irregular galaxies

O and N abundances derived from global emission-line spectra

¹ Main Astronomical Observatory of National Academy of Sciences of Ukraine, 27 Zabolotnogo str., 03680 Kiev, Ukraine e-mail: pilyugin@mao.kiev.ua
² Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées, UMR 5572, 14 avenue E. Belin, 31400 Toulouse, France e-mail: contini@ast.obs-mip.fr
³ Instituto de Astrofísica de Andalucía, CSIC, Apdo 3004, 18080 Granada, Spain e-mail: jvm@iaa.es

Received: 25 November 2003
Accepted: 4 April 2004

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 H ii regions in irregular and spiral galaxies. The conclusion of Kobulnicky et al. ([CITE], ApJ, 514, 544) 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 H ii 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 H ii regions in nearby galaxies. Finally, we show that intermediate-redshift galaxies systematically deviate from the metallicity-luminosity trend of local galaxies.