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

Ryan L. Sanders, Alice E. Shapley, Naveen A. Reddy, Mariska Kriek, Brian Siana, Alison L. Coil, Bahram Mobasher, Irene Shivaei, William R. Freeman, Mojegan Azadi, Sedona H. Price, Gene Leung, Tara Fetherolf, Laura de Groot, Tom Zick, Francesca M. Fornasini, Guillermo Barro

Research output: Contribution to journalArticlepeer-review

122 Scopus citations

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.

Original languageEnglish
Pages (from-to)1427-1455
Number of pages29
JournalMonthly Notices of the Royal Astronomical Society
Volume491
Issue number1
DOIs
StatePublished - Jan 1 2020

Bibliographical note

Publisher Copyright:
© 2019 The Author(s)

Keywords

  • Galaxies: abundances
  • Galaxies: high-redshift

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Fingerprint

Dive into the research topics of 'The MOSDEF survey: Direct-method metallicities and ISM conditions at z ∼ 1.5-3.5'. Together they form a unique fingerprint.

Cite this