TY - JOUR
T1 - On the evolution of helium in blue compact galaxies
AU - Fields, Brian D.
AU - Olive, Keith A.
PY - 1998
Y1 - 1998
N2 - We discuss the chemical evolution of dwarf irregular and blue compact galaxies in light of recent data, new stellar yields, and chemical evolution models. We examine the abundance data for evidence of H II region self-enrichment effects, which would lead to correlations in the scatter of helium, nitrogen, and oxygen abundances around their mean trends. The observed helium abundance trends show no such correlations, although the nitrogen-oxygen trend does show strong evidence for real scatter beyond observational error. We construct simple models for the chemical evolution of these galaxies, using the most recent yields of 4He, C, N, and O in intermediate- and high-mass stars. The effects of galactic outflows, which can arise both from bulk heating and evaporation of the interstellar medium and from the partial escape of enriched supernova ejecta are included. In agreement with other studies, we find that supernova-enriched outflows can roughly reproduce the observed He, C, N, and O trends; however, in models that fit N versus O, the slopes ΔY/ΔO and ΔY/ΔN consistently fall more than 2 σ below the fit to observations. We discuss the role of the models and their uncertainties in the extrapolation of primordial helium from the data. We also explore the model dependence arising from nucleosynthesis uncertainties associated with nitrogen yields in intermediate-mass stars, the fate of 8-11 M⊙ stars, and massive star winds.
AB - We discuss the chemical evolution of dwarf irregular and blue compact galaxies in light of recent data, new stellar yields, and chemical evolution models. We examine the abundance data for evidence of H II region self-enrichment effects, which would lead to correlations in the scatter of helium, nitrogen, and oxygen abundances around their mean trends. The observed helium abundance trends show no such correlations, although the nitrogen-oxygen trend does show strong evidence for real scatter beyond observational error. We construct simple models for the chemical evolution of these galaxies, using the most recent yields of 4He, C, N, and O in intermediate- and high-mass stars. The effects of galactic outflows, which can arise both from bulk heating and evaporation of the interstellar medium and from the partial escape of enriched supernova ejecta are included. In agreement with other studies, we find that supernova-enriched outflows can roughly reproduce the observed He, C, N, and O trends; however, in models that fit N versus O, the slopes ΔY/ΔO and ΔY/ΔN consistently fall more than 2 σ below the fit to observations. We discuss the role of the models and their uncertainties in the extrapolation of primordial helium from the data. We also explore the model dependence arising from nucleosynthesis uncertainties associated with nitrogen yields in intermediate-mass stars, the fate of 8-11 M⊙ stars, and massive star winds.
KW - Galaxies: ISM
KW - Galaxies: abundances
KW - H II regions
KW - Nuclear reactions, nucleosynthesis, abundances
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U2 - 10.1086/306248
DO - 10.1086/306248
M3 - Article
AN - SCOPUS:22444454944
SN - 0004-637X
VL - 506
SP - 177
EP - 190
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1 PART I
ER -