EPOCHS VI: The Size and Shape Evolution of Galaxies since z ~ 8 with JWST Observations

TL;DR

This study analyzes the size and structural evolution of over 1,300 galaxies from redshift 0.5 to 8 using JWST data, revealing that galaxies become smaller over time and exhibit distinct size-mass relationships at different epochs.

Contribution

It provides the first comprehensive analysis of galaxy size evolution up to redshift 8 with JWST, highlighting changes in size, structure, and the size-mass relationship at early cosmic times.

Findings

Galaxies get smaller with increasing redshift, following a (1+z)^{-0.71} trend.

Most high-redshift massive galaxies have low Sersic indices, indicating less concentrated light profiles.

The size-mass relationship breaks down at z > 3, with galaxies of similar sizes regardless of mass or star formation rate.

Abstract

We present the results of a size and structural analysis of 1395 galaxies at $0.5 \leq z \lesssim 8$ with stellar masses $\log \left(M_* / M_{\odot}\right)$ $>$ 9.5 within the JWST Public CEERS field that overlaps with the HST CANDELS EGS observations. We use GALFIT to fit single S\'ersic models to the rest-frame optical profile of our galaxies, which is a mass-selected sample complete to our redshift and mass limit. Our primary result is that at fixed rest-frame wavelength and stellar mass, galaxies get progressively smaller, evolving as $\sim (1+z)^{-0.71\pm0.19}$ up to $z \sim 8$. We discover that the vast majority of massive galaxies at high redshifts have low S\'ersic indices, thus do not contain steep, concentrated light profiles. Additionally, we explore the evolution of the size-stellar mass relationship, finding a correlation such that more massive systems are larger up to $z \sim 3$. This relationship breaks down at $z > 3$, where we find that galaxies are of similar sizes, regardless of their star formation rates and S\'ersic index, varying little with mass. We show that galaxies are more compact at redder wavelengths, independent of sSFR or stellar mass up to $z \sim 3$. We demonstrate the size evolution of galaxies continues up to $z \sim 8$, showing that the process or causes for this evolution is active at early times. We discuss these results in terms of ideas behind galaxy formation and evolution at early epochs, such as their importance in tracing processes driving size evolution, including minor mergers and AGN activity.