Galaxies dwarf irregular

Dwarf galaxies are common objects in the nearby universe. They present a well pronounced dichotomy between the two main classes of dwarf spheroidals (Matteucci, these proceedings) and dwarf irregulars (DIGs). 

Fig. 11.2. Mean stellar iron abundances as a function of luminosity in dwarf spheroidals (filled circles), dwarf ellipticals (open circles), dSph/dlrr transition galaxies (filled diamonds) and dwarf irregulars (open diamonds). Baryonic luminosity in the right panel includes the additional luminosity that irregulars would have if their gas were converted into stars. After Grebel, Gallagher and Harbeck (2003).

In these lectures I present a highly opinionated review of the observed patterns of metallicity and element abundance ratios in nearby spiral, irregular, and dwarf elliptical galaxies, with connection to a number of astrophysical issues associated with chemical evolution. I also discuss some of the observational and theoretical issues associated with measuring abundances in H II regions and gas and stellar surface densities in disk galaxies. Finally, I will outline a few open questions that deserve attention in future investigations. 

Is there zero metallicity gas (or stars for that matter) in galaxies Pre-enrichment by an initial stellar Population III also provides a solution to the G-dwarf problem and to the origin of metals seen in Lya forest clouds. What is the composition of the huge gas reservoirs in the outer parts of spirals and irregulars ... 

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