The metallicity-luminosity relationship of dwarf irregular galaxies - II. A new approach

The nature of a possible correlation between metallicity and luminosity for dwarf irregular galaxies, including those with the highest luminosities, has been explored using simple chemical evolutionary models. Our models depend on a set of free parameters in order to include infall and outflows of gas and covering a broad variety of physical situations. Given a fixed set of parameters, a non-linear correlation between the oxygen abundance and the luminosity may be established. This would be the case if an effective self-regulating mechanism between the accretion of mass and the wind energized by the star formation could lead to the same parameters for all the dwarf irregular galaxies. In the case that these parameters were distributed in a random manner from galaxy to galaxy, a significant scatter in the metallicity-luminosity diagram is expected. Comparing with observations, we show that only variations of the stellar mass-to-light ratio are sufficient to explain the observed scattering and, therefore, the action of a mechanism of self-regulation cannot be ruled out. The possible origin of discrepancies in the metallicity-luminosity correlation found by different authors is discussed.