The JWST Hubble Sequence: The Rest-frame Optical Evolution of Galaxy Structure at 1.5 < z < 6.5

Abstract

We present results on the morphological and structural evolution of a total of 3956 galaxies observed with JWST at 1.5 &lt; z &lt; 6.5 in the JWST CEERS observations that overlap with the CANDELS EGS field. This is the biggest visually classified sample observed with JWST yet, ∼20 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 at producing disk/spheroid/peculiar classifications, whereby we determine how the relative number of these morphologies has evolved since the Universe’s first billion years. Additionally, we explore structural and quantitative morphology measurements using Morfometryka, and show that galaxies with M * &gt; 109 M ⊙ at z &gt; 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 = 6 in this mass range. We also find that the stellar mass and star formation rate densities are dominated by disk galaxies up to z ∼ 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.

The Structure and Morphology of Galaxies during the Epoch of Reionization Revealed by JWST

“…If, on the other hand, we conservatively require that the galaxy has both n < 1.5 and q < 0.6, then we can place a firm lower limit of ∼45% on the incidence of galactic disks in our sample. In agreement with other recent analyses of high-redshift galaxies based on CEERS (Ferreira et al 2022(Ferreira et al , 2023Jacobs et al 2023;Nelson et al 2023;Kartaltepe et al 2023;Robertson et al 2023), the incidence of disky galaxies at this early cosmic epoch is much higher than expected based on previous HST studies (e.g., Kartaltepe et al 2015). Differences in the depth and wavelength coverage between JWST and HST may contribute to this apparent discrepancy in disk fraction detected from the two missions.…”

“…If we adopt a fiducial criterion of n < 1.5 to designate a disky morphology, the fraction of disk-dominated galaxies, for both mass bins combined, roughly doubles from ∼30% at z = 6-9.5 to ∼60% at z = 4-6. Our results qualitatively agree with those of Ferreira et al (2023) and Kartaltepe et al (2023) based on visual classifications. However, for the low-mass and highmass bins, the difference between the median values of n at z  6 and z = 4-6 is only 0.55σ and 1.45σ, respectively (the xσ difference is calculated as x m m…”

The Physical Thickness of Stellar Disks to z ∼ 2

“…With the near-infrared imaging capabilities of JWST/ NIRCam + NIRISS and imaging observations from a number of large public programs available (e.g., CEERS, PRIMER, COSMOS-Web, and UNCOVER), it is now possible to extend this study to earlier cosmic times at z > 3. Early findings from these and other programs are indicating a surprisingly high fraction of morphologically regular stellar disks at these redshifts (Ferreira et al 2022(Ferreira et al , 2023Kartaltepe et al 2023;Robertson et al 2023). It is not yet clear how the detailed physical structures of these galaxies are connected with the structures of the galaxy populations studied in this paper at later cosmic times.…”

Star Formation and AGN Activity 500 Myr after the Big Bang: Insights from JWST

“…On the contrary, Harikane et al (2023b) concluded that 9/10 of their z ≈ 12-16 galaxies cannot possess significant AGN, and thus cannot explain the offset with the constant efficiency model as a result of AGN contamination, on account of their extended morphologies. Indeed, recent results with JWST have shown that galaxy disks were already in place at z ≈ 5-8 (Ferreira et al 2023;Ormerod et al 2024). This implies that the relative weight to the entire morphology of a central point source (AGN) compared to an extended structure (SFR) would be low in these galaxies.…”