A recalibration of strong-line oxygen abundance diagnostics via the direct method and implications for the high-redshift universe

• Published in: Monthly notices of the Royal Astronomical Society Vol. 458; no. 2; pp. 1529 - 1547
• Main Authors: Brown, Jonathan S., Martini, Paul, Andrews, Brett H.
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 11-05-2016
• Subjects: Abundance; Astronomy; Calibration; Diagnostic systems; Emission; Galaxies; Oxygen; Red shift; Spectrum analysis; Star formation; Universe; galaxies: abundances; galaxies: active; galaxies: evolution; galaxies: ISM; ISM: abundances
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stw392

We use direct method oxygen abundances in combination with strong optical emission lines, stellar masses (M
⋆), and star formation rates (SFRs) to recalibrate the N2, O3N2, and N2O2 oxygen abundance diagnostics. We stack spectra of ∼200 000 star-forming galaxies from the Sloan Digital Sky Survey in bins of M
⋆ and SFR offset from the star-forming main sequence (
$ {\Delta \log (SSFR)}$
) to measure the weak emission lines needed to apply the direct method. All three new calibrations are reliable to within ±0.10 dex from log (M
⋆/M⊙) ∼ 7.5–10.5 and up to at least 200 M⊙ yr−1 in SFR. The N2O2 diagnostic is the least subject to systematic biases. We apply the diagnostics to galaxies in the local Universe and investigate the M
⋆–Z–SFR relation. The N2 and O3N2 diagnostics suggest the SFR dependence of the M
⋆–Z–SFR relation varies with both M
⋆ and
${\Delta \log (SSFR)}$
, whereas the N2O2 diagnostic suggests a nearly constant dependence on SFR. We apply our calibrations to a sample of high-redshift galaxies from the literature, and find them to be metal-poor relative to local galaxies with similar M
⋆ and SFR. The calibrations do reproduce direct method abundances of the local analogues. We conclude that the M
⋆–Z–SFR relation evolves with redshift.