Oxygen abundances in dwarf irregular galaxies and the metallicity-luminosity relationship

Main Astronomical Observatory of National Academy of Sciences of Ukraine, Goloseevo, 03680 Kiev-127, Ukraine

Received: 20 December 2000
Accepted: 2 May 2001

Abstract

The low-luminosity dwarf irregular galaxies are considered. The oxygen abundances in H ii regions of dwarf irregular galaxies were recalculated from published spectra through the recently suggested P-method. It has been found that the metallicity of low-luminosity dwarf irregular galaxies, with a few exceptions, correlates well with galaxy luminosity. The dispersion of oxygen abundances around the metallicity-luminosity relationship increases with decreasing galaxy luminosity, as was found by Richer & McCall (1995). The absence of a relationship between the oxygen abundance and the absolute magnitude in the blue band for irregular galaxies obtained by Hidalgo-Gámez & Olofsson (1998) can be explained by the large uncertainties in the oxygen abundances derived through the T_e-method, that in turn can be explained by the large uncertainties in the measurements of the strengths of the weak oxygen line used in the T_e-method.