Chemical Evolution of Late-Type Dwarfs

Abstract

After reviewing some general properties of late-type dwarf galaxies, we present and discuss chemical evolution models for two windy starburst dwarfs: NGC 1569 and NGC1705. Both have their recent star formation history and stellar initial mass function derived from color-magnitude diagram analysis. In order to reproduce the available observations, we must take into account the presence of dark matter halos and the development of late galactic winds. Two possible solutions are envisaged which might explain the origin of the different N/O ratios observed in NGC1569 and NGC1705: either (i) small variations in the stellar initial mass spectrum, leading to the production of different amounts of nitrogen and oxygen from intermediate- and highmass stars; or (ii) the complex interplay among the mechanisms determining cooling and heating of the gas and its conversion into stars. Although the second is by far the most effective in determining the global properties of these galaxies, it still remains also the most elusive.