Abstract
We use photoionization models that are designed to reconcile the joint rest-UV-optical spectra of high-z star-forming galaxies to self-consistently infer the gas chemistry and nebular ionization and excitation conditions for ∼150 galaxies from the Keck Baryonic Structure Survey (KBSS), using only observations of their rest-optical nebular spectra. We find that the majority of z ∼ 2-3 KBSS galaxies are moderately O-rich, with an interquartile range in 12 + log(O/H) = 8.29-8.56, and have significantly sub-solar Fe enrichment, with an interquartile range of [Fe/H] = [-0.79, -0.53], which contributes additional evidence in favor of super-solar O/Fe in high-z galaxies. The model-inferred ionization parameters and N/O are strongly correlated with common strong-line indices (such as O32 and N2O2), with the latter exhibiting similar behavior to local extragalactic H ii regions. In contrast, diagnostics commonly used for measuring gas-phase O/H (such as N2 and O3N2) show relatively large scatter with the overall amount of oxygen present in the gas and behave differently than observed at z ∼ 0. We provide a new calibration for using R23 to measure O/H in typical high-z galaxies, although it is most useful for relatively O-rich galaxies; combining O32 and R23 does not yield a more effective calibration. Finally, we consider the implications for the intrinsic correlations between physical conditions across the galaxy sample and find that N/O varies with O/H in high-z galaxies in a manner that is almost identical to local H ii regions. However, we do not find a strong anti-correlation between ionization parameter and metallicity (O/H or Fe/H) in high-z galaxies, which is one of the principal bases for using strong-line ratios to infer oxygen abundance.
| Original language | English (US) |
|---|---|
| Article number | 117 |
| Journal | Astrophysical Journal |
| Volume | 868 |
| Issue number | 2 |
| DOIs | |
| State | Published - Dec 1 2018 |
Funding
The data presented in this paper were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. This work has been supported in part by a US National Science Foundation (NSF) Graduate Research Fellowship (A.L.S.), by the NSF through grants AST-0908805 and AST-1313472 (C.C.S. and A.L.S.). Finally, the authors wish to recognize and acknowledge the significant cultural role and reverence that the summit of Maunakea has within the indigenous Hawaiian community. We are privileged to have the opportunity to conduct observations from this mountain.
Keywords
- H II regions
- ISM: abundances
- cosmology: observations
- galaxies: ISM
- galaxies: evolution
- galaxies: high-redshift
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science