Panic! At the Disks: First Rest-frame Optical Observations of Galaxy Structure at $z > 3$ with JWST in the SMACS 0723 Field

TL;DR

This study uses JWST observations to analyze galaxy structures at redshifts greater than 3, revealing that disk galaxies are more prevalent at these early cosmic times than previously observed with Hubble, providing new insights into galaxy evolution.

Contribution

First optical morphological analysis of high-redshift galaxies with JWST, showing a dominance of disk galaxies at z > 1.5, contrasting earlier Hubble results.

Findings

Disk galaxies dominate at z > 1.5.

JWST reveals a tenfold increase in disk galaxy fraction compared to Hubble.

Visual and quantitative morphologies are consistent.

Abstract

We present early results regarding the morphological and structural properties of galaxies seen with the James Webb Space Telescope at $z > 3$ in the Early Release Observations of SMACS 0723, a galaxy cluster at $z=0.39$. We investigate, for the first time, the optical morphologies of a significant number of $z > 3$ galaxies with accurate photometric redshifts in this field to determine the form of galaxy structure in the relatively early universe. We use visual morphologies and \textsc{Morfometryka} measures to perform quantitative morphology measurements, both parametric with light profile fitting (S\'ersic indices) and non-parametric (CAS values). Using these, we measure the relative fraction of disk, spheroidal, and peculiar galaxies at $3 < z < 8$. We discover the surprising result that at $z > 1.5$ disk galaxies dominate the overall fraction of morphologies, with a factor of $\sim 10$ relative higher number of disk galaxies than seen by the Hubble Space Telescope at these redshifts. Our visual morphological estimates of galaxies align closely with their locations in CAS parameter space and their S\'ersic indices.