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The oxygen abundance calibrations and N/O abundance ratios of ~40,000 SDSS star-forming galaxies

Y. C. Liang·S. Y. Yin·F. Hammer·L. C. Deng·H. Flores·B. Zhang
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Abstract

Using a large sample of 38,478 star-forming galaxies selected from the Second Data Release of the Sloan Digital Sky Survey database (SDSS-DR2), we derive analytical calibrations for oxygen abundances from several metallicity-sensitive emission-line ratios: [N II]/H_alpha, [O III]/[N II], [N II]/[O II], [N II]/[S II], [S II]/H_alpha, and [O III]/H_beta. 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 (8.4<12+log(O/H)<9.3), and for the nuclear regions of galaxies. The observed relations are consistent with those expected from the photoionization models of Kewley & Dopita (2002). However, most of the observational data spread in a range of ionization parameter q from 1*10^7 to 8*10^7 cm s^{-1}, corresponding to logU= -3.5 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" components of nitrogen.

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Y. C. Liang, S. Y. Yin, F. Hammer, L. C. Deng, H. Flores, B. Zhang. 2006-07-05. The oxygen abundance calibrations and N/O abundance ratios of ~40,000 SDSS star-forming galaxies. https://doi.org/10.1086/507592

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