Volume 652, number 1: The Oxygen Abundance Calibrations and N/O Abundance Ratios of ~40,000 SDSS Star-forming Galaxies
16th Nov 2006, 17:54 GMT
Using a large sample of 38,478 star-forming galaxies selected from SDSS DR2, we derive analytical calibrations for oxygen abundances from several metallicity-sensitive emission-line ratios: [N ii]/Hα, [O iii]/[N ii], [N ii]/[O ii], [N ii]/[S ii], [S ii]/Hα, and [O iii]/Hβ. This consistent set of strong-line oxygen abundance calibrations will be useful for future abundance studies. Among these calibrations, [N ii]/[O ii] is the best for metal-rich galaxies due to its independence on ionization parameter and low scatter. Dust extinction must be considered properly at first. These calibrations are more suitable for metal-rich galaxies [[FORMULA]] and for the nuclear regions of galaxies. The observed relations are consistent with those expected from the photoionization models of Kewley & Dopita. However, most of the observational data spread in a range of ionization parameter q from [FORMULA] to [FORMULA] cm s−1, corresponding to [FORMULA] to −2.5, narrower than that suggested by the models. We also estimate the (N/O) abundance ratios of this large sample of galaxies, and these are consistent with the combination of a “primary” and a dominant “secondary” component of nitrogen.
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