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arXiv · 2207.12430

A Preview of JWST Metallicity Studies at Cosmic Noon: The First Detection of Auroral [O II] Emission at High Redshift

Ryan L. Sanders·Alice E. Shapley·Leonardo Clarke·Michael W. Topping·Naveen A. Reddy·Mariska Kriek·Tucker Jones·Daniel P. Stark·Mengtao Tang
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Abstract

We present ultra-deep 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~hours 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]$λλ$7322,7332 lines at high redshift. We use these measurements to calculate the electron temperature in the low-ionization O$^+$ zone of the ionized ISM 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 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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Ryan L. Sanders, Alice E. Shapley, Leonardo Clarke, Michael W. Topping, Naveen A. Reddy, Mariska Kriek, Tucker Jones, Daniel P. Stark, Mengtao Tang. 2022-07-25. A Preview of JWST Metallicity Studies at Cosmic Noon: The First Detection of Auroral [O II] Emission at High Redshift. https://doi.org/10.3847/1538-4357%2Faca9cc

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