Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aj....117.2789h&link_type=abstract
The Astronomical Journal, Volume 117, Issue 6, pp. 2789-2809.
Astronomy and Astrophysics
Astronomy
67
Ism: Dust, Extinction, Galaxies: Abundances, Galaxies: Irregular, Ism: H Ii Regions
Scientific paper
We present reddenings and abundances of 189 H II regions measured from 203 emission-line spectra in a sample of 65 irregular (Im), blue compact dwarf (BCD), and Sm galaxies. In most of these spectra we measure [O III] lambda5007, Hβ, [N II] lambda6584, and [S II] lambdalambda6717, 6731; in 24 spectra we measure [O II] lambda3727 and in five we measure [O III] lambda4363. The internal reddenings of the galaxies are used to determine whether redder irregular galaxies are also dustier than bluer irregulars. We find that the range in optical broadband colors among Im galaxies is most likely dominated by differences in the contributions of the massive star population or the effects of abundances, while the range in colors of BCDs does show evidence consistent with a contribution from dustiness. We use the abundances to confirm that our sample of BCD galaxies, selected to be comparable to Im systems in other global properties, are also comparable in abundances and, hence, evolutionary status. Finally, we explore relationships between abundances and other global galactic properties and find few convincing correlations. However, bluer galaxies tend to be more metal-poor. There is a slight trend of higher relative gas content with lower abundances among the BCD sample, but not in the Im sample. The difference could be due to a difference in gas distributions and the fraction of total gas that is actively participating in the chemical evolution of the galaxy. In addition, our BCD, but not our Im, sample of galaxies are consistent by themselves with the galactic luminosity-metallicity relationship determined by others, but the Im sample is consistent with the general trend seen over a large baseline when combined with spiral galaxies. However, the scatter is large.
Hoffman Loren
Hunter Deidre Ann
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