The MOSDEF survey: Direct-method metallicities and ISM conditions at z ∼ 1.5-3.5

Authors

• Ryan L. Sanders, University of California, Davis
• Alice E. Shapley, University of California, Los Angeles
• Naveen A. Reddy, University of California, Riverside
• Mariska Kriek, University of California, Berkeley
• Brian Siana, University of California, Riverside
• Alison L. Coil, University of California, San Diego
• Bahram Mobasher, University of California, Riverside
• Irene Shivaei, The University of Arizona
• William R. Freeman, University of California, Riverside
• Mojegan Azadi, Harvard-Smithsonian Center for Astrophysics
• Sedona H. Price, Max Planck Institute for Extraterrestrial Physics
• Gene Leung, University of California, San Diego
• Tara Fetherolf, University of California, Riverside
• Laura de Groot, The College of Wooster
• Tom Zick, University of California, Berkeley
• Francesca M. Fornasini, Harvard-Smithsonian Center for Astrophysics
• Guillermo Barro, University of the PacificFollow

Document Type

Article

Publication Title

Monthly Notices of the Royal Astronomical Society

Department

Physics

ISSN

13652966

Volume

491

Issue

1

DOI

10.1093/mnras/stz3032

First Page

1427

Last Page

1455

Publication Date

11-4-2019

Abstract

We present detections of [O III] λ4363 and direct-method metallicities for star-forming galaxies at z = 1.7-3.6. We combine new measurements from the MOSFIRE Deep Evolution Field (MOSDEF) survey with literature sources to construct a sample of 18 galaxies with direct-method metallicities at z > 1, spanning 7.5 < 12+log(O/H) < 8.2 and log(M∗/M☉) = 7-10. We find that strong-line calibrations based on local analogues of high-redshift galaxies reliably reproduce the metallicity of the z > 1 sample on average. We construct the first mass-metallicity relation at z > 1 based purely on direct-method O/H, finding a slope that is consistent with strong-line results. Direct-method O/H evolves by ≲0.1 dex at fixed M∗ and star formation rate from z ∼ 0 to 2.2. We employ photoionization models to constrain the ionization parameter and ionizing spectrum in the high-redshift sample. Stellar models with supersolar O/Fe and binary evolution of massive stars are required to reproduce the observed strong-line ratios. We find that the z > 1 sample falls on the z ∼ 0 relation between ionization parameter and O/H, suggesting no evolution of this relation from z ∼ 0 to z ∼ 2. These results suggest that the offset of the strong-line ratios of this sample from local excitation sequences is driven primarily by a harder ionizing spectrum at fixed nebular metallicity compared to what is typical at z ∼ 0, naturally explained by supersolar O/Fe at high redshift caused by rapid formation time-scales. Given the extreme nature of our z > 1 sample, the implications for representative z ∼ 2 galaxy samples at ∼10¹⁰ M☉ are unclear, but similarities to z > 6 galaxies suggest that these conclusions can be extended to galaxies in the epoch of reionization.

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 International License.

Recommended Citation

Sanders, Ryan L.; Shapley, Alice E.; Reddy, Naveen A.; Kriek, Mariska; Siana, Brian; Coil, Alison L.; Mobasher, Bahram; Shivaei, Irene; Freeman, William R.; Azadi, Mojegan; Price, Sedona H.; Leung, Gene; Fetherolf, Tara; de Groot, Laura; Zick, Tom; Fornasini, Francesca M.; and Barro, Guillermo, "The MOSDEF survey: Direct-method metallicities and ISM conditions at z ∼ 1.5-3.5" (2019). Pacific Faculty Work. 294.
https://scholarlycommons.pacific.edu/all-faculty/294