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Date and Time of the Query: 2019-06-19 T02:54:09 PDT
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For refcode 2002MNRAS.330...69D:
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Copyright by Royal Astronomical Society. 2002MNRAS.330...69D New light on the search for low-metallicity galaxies - I. The N2 calibrator Glenda Denicolo, Roberto Terlevich and Elena Terlevich ABSTRACT We present a simple metallicity estimator based on the logarithmic [N II] {lambda}6584/H{alpha} ratio, hereafter N2, which we envisage will become very useful for ranking galaxies in a metallicity sequence from redshift survey-quality data even for moderately low spectral resolution. We have calibrated the N2 estimator using a compilation of H II galaxies having accurate oxygen abundances, plus photoionization models covering a wide range of abundances. The comparison of models and observations indicates that both primary and secondary nitrogen are important for the relevant range of metallicities. The N2 estimator follows a linear relation with log(O/H) that holds for the whole abundance range covered by the sample, from approximately 1/50th to twice the Solar value [7.2 < 12 + log(O/H) < 9.1]. We suggest that the ([S II] {lambda}{lambda}6717,6731/H{alpha}) ratio (hereafter S2) can also be used as a rough metallicity indicator. Because of its large scatter the S2 estimator will be useful only in systems with very low metallicity, where [N II] {lambda}6584 is not detected or in low-resolution spectra where [N II] {lambda}6584 is blended with H{alpha}. Keywords: galaxies: abundances - galaxies: evolution - galaxies: stellar content.
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