On the mass–metallicity–star formation rate relation for galaxies at z∼2
- Department of Astronomy, Indiana University, Bloomington, IN 47404 (United States)
- Space Telescope Science Institute, Baltimore, MD 21218 (United States)
- University of the Western Cape, Bellville, Cape Town 7535 (South Africa)
- National Optical Astronomy Observatory, Tucson, AZ 85719 (United States)
Recent studies have shown that the local mass–metallicity (M{sub *}–Z) relation depends on the specific star formation rate (sSFR). Whether such a dependence exists at higher redshifts, and whether the resulting M{sub *}–Z–SFR relation is redshift invariant, is debated. We re-examine these issues by applying the non-parametric techniques of Salim et al. to ∼130 z∼2.3 galaxies with N2 and O3 measurements from Keck Baryonic Structure Survey (KBSS). We find that the KBSS M{sub *}–Z relation depends on sSFR at intermediate masses where such dependence exists locally. KBSS and SDSS galaxies of the same mass and sSFR (“local analogs”) are similarly offset in the BPT diagram relative to the bulk of local star-forming galaxies, and thus we posit that metallicities can be compared self-consistently at different redshifts as long as the masses and sSFRs of the galaxies are similar. We find that the M{sub *}–Z–SFR relation of z∼2 galaxies is consistent with the local one at logM{sub ∗}<10, but is offset up to −0.25 dex at higher masses, so it is altogether not redshift invariant. This high-mass offset could arise from a bias that [O iii]-based, high-redshift spectroscopic surveys have against high-metallicity galaxies, but additional evidence disfavors this possibility. We identify three causes for the reported discrepancy between N2 and O3N2 metallicities at z∼2: (1) a smaller offset that is also present for SDSS galaxies, which we remove with new N2 calibration, (2) a genuine offset due to differing ISM condition, which is also present in local analogs, and (3) an additional offset due to unrecognized active galactic nucleus contamination.
- OSTI ID:
- 22882892
- Journal Information:
- Astrophysical Journal, Vol. 808, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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