# On the stunning abundance of super-early, massive galaxies revealed by JWST

**Authors:** A. Ferrara, A. Pallottini, P. Dayal  
**arXiv:** [2208.00720](https://arxiv.org/abs/2208.00720)  
**Date:** 2022-08-01  
**Summary page:** https://www.summarizepaper.com/en/paper/2208.00720v1/

## Key points

- Recent observations from the James Webb Space Telescope (JWST) have found a surprising number of super-early, massive galaxies at high redshifts ($z>10$)
- These galaxies have a mass of approximately $10^9$ times that of our Sun and are extremely bright in the ultraviolet (UV) range with a magnitude of around -21
- The authors propose a minimal physical model that combines the halo mass function and an obscured star formation fraction prescription to explain this phenomenon
- The model has been successfully tested on UV luminosity functions up to $z=7$
- The weak evolution observed from $z=7$ to $z\approx 14$ at the bright end of the luminosity function is attributed to a delicate balance between decreasing dust attenuation and an increasing shortage of host halos
- The model predicts that galaxies at even higher redshifts ($z>11$) should contain negligible amounts of dust, possibly due to efficient ejection during galaxy formation
- Uncertainties still exist in data analysis, but various possibilities are being explored to explain this unexpected abundance, including denser dark matter halos or astrophysical factors such as high gas-to-star conversion efficiency or unconventional properties of the stellar population
- The authors' interpretation provides an explanation for the observed galaxy abundance at $z=10-14$, highlighting the need for further investigation and theoretical exploration.

## Summary

The recent observations from the James Webb Space Telescope (JWST) have uncovered a surprising number of super-early, massive galaxies at high redshifts ($z>10$). These galaxies have a mass of approximately $10^9$ times that of our Sun and are extremely bright in the ultraviolet (UV) range with a magnitude of around -21. This unexpected abundance of bright galaxies at such early cosmic times has raised questions and prompted further investigation. To explain this phenomenon, the authors present a minimal physical model that combines two key components. Firstly, they consider the halo mass function, which describes the distribution of dark matter halos in the universe. Secondly, they incorporate an obscured star formation fraction prescription based on findings from the ALMA REBELS dusty galaxy survey. This prescription accounts for the fraction of star formation activity that is hidden by dust. The proposed model has been successfully tested on well-known UV luminosity functions (LFs) up to $z=7$. The weak evolution observed from $z=7$ to $z\approx 14$ at the bright end of the LF is attributed to a delicate balance between decreasing dust attenuation (which makes galaxies brighter) and an increasing shortage of their host halos. This intriguing interplay between dust attenuation and halo scarcity explains why these super-early massive galaxies remain visible despite their increasingly rare environments. Furthermore, the model predicts that galaxies at even higher redshifts ($z>11$) should contain negligible amounts of dust. The authors speculate that this lack of dust could be due to efficient ejection during the initial phases of galaxy formation. The discovery of these super-early, massive galaxies challenges current understanding and calls for theoretical clarification. While uncertainties still exist in data analysis, it is crucial to explore various possibilities to explain this unexpected abundance. One possibility is that dark matter halos may be denser than predicted by current models; however, astrophysical factors are more likely to play a significant role, such as a high gas-to-star conversion efficiency at high redshifts or unconventional properties of the stellar population. In conclusion, the authors provide an interpretation for the surprising abundance of super-early massive galaxies observed by JWST. Their minimal physical model, combining the halo mass function and an obscured star formation fraction prescription, successfully explains the observed galaxy abundance at $z=10-14$. This study highlights the need for further investigation and theoretical exploration to fully understand the nature and formation of these intriguing galaxies.