On the Oxygen Abundance of Neutral Gas in I Zw 18
Max Pettini, Keith Lipman
Abstract
Whether the H II regions of dwarf emission-line galaxies are self-polluted by the nucleosynthetic products of massive stars remains an open question, despite recent claims to the contrary. We show that the finding by Kunth and collaborators that the neutral interstellar medium of I Zw 18 has a metallicity one order of magnitude lower than that of the ionized gas is highly uncertain. The range of possible values of (O/H) admitted by the saturated O I absorption line used in their analysis is very large, spanning a factor of the order of 1000. We suggest that future observations of the intrinsically weaker S II 1256 multiplet offer the best prospects for measuring the true degree of metal enrichment of this dwarf galaxy.
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