Finding Peas in the Early Universe with JWST

TL;DR

This paper analyzes early JWST spectra of three $z \sim ext{8}$ galaxies to determine their physical properties, revealing similarities with nearby Green Pea galaxies and providing insights into epoch-of-reionization galaxies.

Contribution

First detailed rest-optical emission line spectroscopy of $z \sim ext{8}$ galaxies using JWST, linking them to local Green Pea galaxies and advancing understanding of reionization-era galaxy properties.

Findings

Galaxies have metallicities $12+ ext{log}[O/H] ext{ } ext{approx} ext{ }6.9-8.2$.

Spectra show similarities to Green Pea galaxies in metallicity and morphology.

Evidence suggests these galaxies are actively driving reionization.

Abstract

The Early Release Observations (EROs) of JWST beautifully demonstrate the promise of JWST in characterizing the universe at cosmic dawn. We analyze the ERO spectra of three $z \sim 8$ galaxies to determine their metallicities, gas temperatures and ionization. These galaxies offer the first opportunity to understand the physical properties of epoch-of-reionization galaxies through detailed rest-optical emission line spectroscopy. We show that these objects have metal abundances $12+\log[O/H] \approx 6.9 - 8.2$, based on both the $T_e$ method and on a recent calibration of the $R_{23}$ metallicity indicator. Since the spectra are some of the earliest science data from JWST, we compare several line ratios with values expected from robust physics, to validate our measurement procedures. We compare the abundances and emission line ratios to a nearby sample of Green Pea galaxies -- a population of nearby emission line galaxies whose UV properties resemble epoch-of-reionization galaxies, and which often have large Lyman continuum escape fractions. The JWST data show striking further similarities between these high redshift galaxies and nearby Green Peas. The $z\sim 8$ galaxies span the metallicity range covered by Green Peas. They also show the compact morphology that is typical of emission line dominated galaxies at all redshifts. Based on these similarities with Green Peas, it is likely that these are the first rest-optical spectra of galaxies that are actively driving cosmological reionization