TY - JOUR
T1 - A Preview of JWST Metallicity Studies at Cosmic Noon
T2 - The First Detection of Auroral [O ii] Emission at High Redshift
AU - Sanders, Ryan L.
AU - Shapley, Alice E.
AU - Clarke, Leonardo
AU - Topping, Michael W.
AU - Reddy, Naveen A.
AU - Kriek, Mariska
AU - Jones, Tucker
AU - Stark, Daniel P.
AU - Tang, Mengtao
N1 - Publisher Copyright:
© 2023. The Author(s). Published by the American Astronomical Society.
PY - 2023/2/1
Y1 - 2023/2/1
N2 - We present ultradeep Keck/MOSFIRE rest-optical spectra of two star-forming galaxies at z = 2.18 in the COSMOS field with bright emission lines, representing more than 20 hr of total integration. The fidelity of these spectra enabled the detection of more than 20 unique emission lines for each galaxy, including the first detection of the auroral [O ii]λλ7322, 7332 lines at high redshift. We use these measurements to calculate the electron temperature in the low-ionization O+ zone of the ionized interstellar medium and derive abundance ratios of O/H, N/H, and N/O using the direct method. The N/O and α/Fe abundance patterns of these galaxies are consistent with rapid formation timescales and ongoing strong starbursts, in accord with their high specific star formation rates. These results demonstrate the feasibility of using auroral [O ii] measurements for accurate metallicity studies at high redshift in a higher-metallicity and lower-excitation regime previously unexplored with the direct method in distant galaxies. These results also highlight the difficulty in obtaining the measurements required for direct-method metallicities from the ground. We emphasize the advantages that the JWST/NIRSpec instrument will bring to high-redshift metallicity studies, where the combination of increased sensitivity and uninterrupted wavelength coverage will yield more than an order of magnitude increase in efficiency for multiplexed auroral-line surveys relative to current ground-based facilities. Consequently, the advent of JWST promises to be the beginning of a new era of precision chemical abundance studies of the early universe at a level of detail rivaling that of local galaxy studies.
AB - We present ultradeep Keck/MOSFIRE rest-optical spectra of two star-forming galaxies at z = 2.18 in the COSMOS field with bright emission lines, representing more than 20 hr of total integration. The fidelity of these spectra enabled the detection of more than 20 unique emission lines for each galaxy, including the first detection of the auroral [O ii]λλ7322, 7332 lines at high redshift. We use these measurements to calculate the electron temperature in the low-ionization O+ zone of the ionized interstellar medium and derive abundance ratios of O/H, N/H, and N/O using the direct method. The N/O and α/Fe abundance patterns of these galaxies are consistent with rapid formation timescales and ongoing strong starbursts, in accord with their high specific star formation rates. These results demonstrate the feasibility of using auroral [O ii] measurements for accurate metallicity studies at high redshift in a higher-metallicity and lower-excitation regime previously unexplored with the direct method in distant galaxies. These results also highlight the difficulty in obtaining the measurements required for direct-method metallicities from the ground. We emphasize the advantages that the JWST/NIRSpec instrument will bring to high-redshift metallicity studies, where the combination of increased sensitivity and uninterrupted wavelength coverage will yield more than an order of magnitude increase in efficiency for multiplexed auroral-line surveys relative to current ground-based facilities. Consequently, the advent of JWST promises to be the beginning of a new era of precision chemical abundance studies of the early universe at a level of detail rivaling that of local galaxy studies.
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U2 - 10.3847/1538-4357/aca9cc
DO - 10.3847/1538-4357/aca9cc
M3 - Article
AN - SCOPUS:85147224809
SN - 0004-637X
VL - 943
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 75
ER -