TY - JOUR
T1 - The MOSDEF survey
T2 - Direct-method metallicities and ISM conditions at z ∼ 1.5-3.5
AU - Sanders, Ryan L.
AU - Shapley, Alice E.
AU - Reddy, Naveen A.
AU - Kriek, Mariska
AU - Siana, Brian
AU - Coil, Alison L.
AU - Mobasher, Bahram
AU - Shivaei, Irene
AU - Freeman, William R.
AU - Azadi, Mojegan
AU - Price, Sedona H.
AU - Leung, Gene
AU - Fetherolf, Tara
AU - de Groot, Laura
AU - Zick, Tom
AU - Fornasini, Francesca M.
AU - Barro, Guillermo
N1 - Publisher Copyright:
© 2019 The Author(s)
PY - 2020/1/1
Y1 - 2020/1/1
N2 - 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.
AB - 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.
KW - Galaxies: abundances
KW - Galaxies: high-redshift
UR - http://www.scopus.com/inward/record.url?scp=85079586631&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85079586631&partnerID=8YFLogxK
U2 - 10.1093/mnras/stz3032
DO - 10.1093/mnras/stz3032
M3 - Article
AN - SCOPUS:85079586631
SN - 0035-8711
VL - 491
SP - 1427
EP - 1455
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 1
ER -