Metallicities of Five z > 5 Emission-line Galaxies in SMACS 0723 Revealed by JWST

JWST's Early Release Observations of the lensing cluster SMACS J0723.3–7327 have given an unprecedented spectroscopic look into the high-redshift universe. These observations reveal five galaxies at z > 5. All five have detectable [O iii]λ4363 line emission, indicating that these galaxies have high temperatures and low metallicities and that they are highly star-forming. In recent work, the metallicities of these five galaxies have been studied using various techniques. Here we summarize and compare these previous results, as well as perform our own measurements of the metallicities using improved methodologies that optimize the extraction of the emission lines. In particular, we use simultaneous line fitting and a fixed Balmer decrement correction, as well as a novel footprint measurement of the emission lines in the 2D spectra, to produce higher-fidelity line ratios that are less sensitive to calibration and systematic effects. We then compare our metallicities to those of z ≲ 1 galaxies with high rest-frame equivalent widths of Hβ, finding that they may be good analogs. Finally, we estimate that the JWST galaxies out to z ∼ 8 are young compared to the age of the universe.