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The [OII]/Halpha ratio of emission line galaxies in the 2dF redshift survey

M. Mouhcine·I. Lewis·B. Jones·F. Lamareille·S. J. Maddox·T. Contini
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Abstract

We investigate the systematic variation of the [OII]3727/Halpha flux line ratio as a function of various galaxy properties, i.e., luminosity, metallicity, reddening, and excitation state, for a sample of 1124 emission-line galaxies, with a mean redshift z ~ 0.06, drawn from the Two Degree Field Galaxy Redshift Survey. The mean observed and extinction-corrected emission-line flux ratios agree well with the values derived from the $B$-band selected Nearby Field Galaxy Survey galaxy sample, but are significantly different from the values obtained from the Halpha-selected Universidad Complutense de Madrid Survey galaxy sample. This is because the different selection criteria applied in these surveys lead to a significant difference in the mean extinction and metallicity of different samples. We use the R_{23} parameter to estimate the gas-phase oxygen abundance and find that the extinction-corrected [OII]3727/Halpha ratio depends on the oxygen abundance. For 12+log(O/H)>8.4, we confirm that the emission-line ratio decreases with increasing metallicity. We have extended the relationship further to the metal-poor regime, 12+log(O/H)< 8.4, and find that the correlation between the extinction-corrected [OII]3727/Halpha ratio and the metallicity reverses in comparison to the relationship for metal-rich galaxies. For metal-poor galaxies, in contrast with metal-rich ones, the variation of extinction-corrected [OII]3727/Halpha ratio is correlated with the ionization states of the interstellar gas.

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M. Mouhcine, I. Lewis, B. Jones, F. Lamareille, S. J. Maddox, T. Contini. 2005-11-29. The [OII]/Halpha ratio of emission line galaxies in the 2dF redshift survey. https://doi.org/10.1111/j.1365-2966.2005.09211.x

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