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

TL;DR

This study uses JWST observations to measure and compare metallicities of five high-redshift galaxies at z > 5, employing improved techniques to enhance accuracy and explore their properties relative to lower-redshift galaxies.

Contribution

The paper introduces novel methodologies for metallicity measurement in high-redshift galaxies, improving accuracy and systematic robustness over previous techniques.

Findings

High-redshift galaxies have low metallicities and high star formation rates.

The metallicities of these galaxies are comparable to z < 1 galaxies with high H-beta equivalent widths.

JWST galaxies at z ~ 8 are inferred to be young relative to the universe's age.

Abstract

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 [OIII]4363 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 H-beta, 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.