The Z-L relationship of dwarf irregular galaxies I. First results

We have revisited the stated relation between the metallicity and the luminosity for nearby dwarf irregular galaxies. A sample based on the absolute magnitude and the radius of the galaxies as observable criteria was selected. New and better distance determinations from the literature were used and the metallicities were recalculated from published spectra. The derived distribution of dwarf galaxies in the Z-L plane is different from the ones previously obtained. A factor which could have bearing on the Z-L relation is the different environment where the galaxies reside. This was investigated using the selected sample but no firm conclusion could be drawn and a more elaborate study should be made using a larger sample. The two parameters mostly used for determining the metallicity and the luminosity are the oxygen abundance and the absolute blue magnitude. In this analysis it is suggested that the nitrogen abundance and the near-infrared absolute magnitude should be used instead. These are less affected by the recent star formation history of the galaxy.