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

**Authors:** Wen Sun, Luis C. Ho, Ming-Yang Zhuang, Chao Ma, Changhao Chen, Ruancun Li  
**arXiv:** [2308.09076](https://arxiv.org/abs/2308.09076)  
**Date:** 2023-08-17  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2308.09076v1/

## Key points

- Study analyzes 347 galaxies at redshifts ranging from $4<z<9.5$
- Two-dimensional parametric model used to fit NIRCam images and measure structural parameters
- Focus on global S\'ersic index ($n$) and observed axial ratio ($q$)
- Galactic disks identified in at least 45% of analyzed galaxies
- Relationship between rest-frame optical luminosity and effective radius ($R_e$) investigated
- Consistent relation found across all redshift intervals studied, with slightly lower zero point in higher redshift bin
- No significant redshift evolution of $n$ or $R_e$ observed at early epochs
- JWST's capabilities greatly contribute to the study by providing superior light-gathering power compared to HST
- JWST allows investigation of rest-frame optical light in galaxies up to $z \approx 9.5$
- Recent results from JWST indicate regular disks are common in galaxies at $z \gtrsim 2$
- Study provides valuable insights into early stages of galaxy formation and evolution

## Summary

In this study, the authors analyze 347 galaxies at redshifts ranging from $4<z<9.5$ using observations from the CEERS program with the James Webb Space Telescope (JWST). They employ a two-dimensional parametric model to fit the seven-filter NIRCam images and measure the overall structural parameters of the galaxies in the rest-frame optical band. The goal is to quantify the global properties of these high-redshift galaxies and derive robust uncertainties that account for various factors, including cosmological surface brightness dimming and resolution effects. The authors focus on two key parameters: the global S\'ersic index ($n$) and observed axial ratio ($q$). By setting thresholds of $n < 1.5$ and $q < 0.6$, they identify galactic disks and find that they are present in at least 45% of the analyzed galaxies, suggesting that galactic disks are relatively common during this epoch. Furthermore, they investigate the relationship between rest-frame optical luminosity and effective radius ($R_e$) for galaxies in different redshift ranges. They find that there is a consistent relation between these two parameters across all redshift intervals studied ($4<z<9.5$, $4 < z < 5$, and $5 \leq z < 9.5$), with a similar slope but a slightly lower zero point in the higher redshift bin ($R_e = 0.49 \pm 0.07$ kpc) compared to the lower redshift bin ($R_e = 0.65 \pm 0.12$ kpc). Importantly, within their current sample size, no significant redshift evolution of $n$ or $R_e$ is observed at these early epochs. The authors highlight that JWST's capabilities greatly contribute to this study by providing superior light-gathering power compared to previous telescopes like Hubble Space Telescope (HST). JWST's extended long-wavelength sensitivity, particularly with its reddest wide filter (F444W) of NIRCam, allows for investigation of rest-frame optical light in galaxies up to $z \approx 9.5$. Contrary to previous assumptions based on HST studies, recent results from JWST indicate that regular disks are common in galaxies at $z \gtrsim 2$. In conclusion, this study presents a detailed analysis of structure and morphology of high-redshift galaxies using JWST observations which suggest a significant presence of galactic disks during this epoch as well as reveal a consistent relationship between rest-frame optical luminosity and effective radius across different redshift intervals; providing valuable insights into early stages of galaxy formation and evolution.