The JWST Hubble Sequence: The Rest-Frame Optical Evolution of Galaxy Structure at $1.5 < z < 8$

TL;DR

This study uses JWST data to analyze the morphological evolution of over 4000 galaxies from redshift 1.5 to 8, revealing that disk galaxies dominated earlier than previously believed and that the Hubble Sequence was established within the first billion years.

Contribution

It provides the largest visually classified galaxy sample at high redshift, demonstrating early dominance of disk galaxies and the early emergence of the Hubble Sequence, with classifications made publicly available.

Findings

Disk galaxies dominate up to z=8, earlier than previously thought.

Stellar mass and star formation are primarily in disk galaxies up to z~6.

The observed galaxy morphology fractions align with cosmological simulations.

Abstract

We present results on the morphological and structural evolution of a total of 4265 galaxies observed with JWST at $1.5 < z < 8$ in the JWST CEERS observations that overlap with the CANDELS EGS field. This is the biggest visually classified sample observed with JWST yet, $\sim20$ times larger than previous studies, and allows us to examine in detail how galaxy structure has changed over this critical epoch. All sources were classified by six individual classifiers using a simple classification scheme aimed to produce disk/spheroid/peculiar classifications, whereby we determine how the relative number of these morphologies evolves since the Universe's first billion years. Additionally, we explore structural and quantitative morphology measurements using \textsc{Morfometryka}, and show that galaxies at $z > 3$ are not dominated by irregular and peculiar structures, either visually or quantitatively, as previously thought. We find a strong dominance of morphologically selected disk galaxies up to $z = 8$, a far higher redshift than previously thought possible. We also find that the stellar mass and star formation rate densities are dominated by disk galaxies up to $z \sim 6$, demonstrating that most stars in the universe were likely formed in a disk galaxy. We compare our results to theory to show that the fraction of types we find is predicted by cosmological simulations, and that the Hubble Sequence was already in place as early as one billion years after the Big Bang. Additionally, we make our visual classifications public for the community.