The chemical abundances in a sample of dwarf irregular galaxies

Abstract

Deep groundbased spectra of Hubble V and Hubble X, the two largest and brightest H ii regions in the Local Group dwarf galaxy, NGC 6822, are presented. The extinction, excitation and ionization are studied on scales as small as 4 pc. The chemical composition of some elements within the regions as well as possible small scale variations in the abundances of helium, nitrogen, oxygen and neon over the face of the two regions are investigated. The detection of the emission lines OI and ClIII are probably related to shock-heating from gas ejected from supernova explosions and planetary nebula ejections, respectively, although the contribution to the total ionization is very small. No significant differences in chemical composition was found between Hubble V and Hubble X. However, some small scale variations in the abundances of oxygen, and possibly nitrogen and helium, over the face of both H ii regions were noted, although different physical conditions could apply within the regions, such as local fluctuations in the temperature.