# Bursty Star Formation Naturally Explains the Abundance of Bright Galaxies at Cosmic Dawn

**Authors:** Guochao Sun, Claude-André Faucher-Giguère, Christopher C. Hayward, Xuejian Shen, Andrew Wetzel, Rachel K. Cochrane  
**arXiv:** [2307.15305](https://arxiv.org/abs/2307.15305)  
**Date:** 2023-07-28  
**Summary page:** https://www.summarizepaper.com/en/paper/2307.15305v1/

## Key points

- Recent discoveries of bright galaxies at cosmic dawn (z ≳ 10) provide insights into galaxy formation models
- The bright end of the galaxy UV luminosity function (UVLF) is higher than predicted by many models
- The authors use 25,000 galaxy snapshots from the FIRE project to investigate this discrepancy
- Observed abundance of UV-bright galaxies can be reproduced in simulations without modifications to standard stellar feedback processes
- Bursty star formation histories predicted by the simulations play a crucial role in reproducing bright-end UVLFs at cosmic dawn
- Comparison between bursty and smoothed star formation histories shows significant changes in the abundance of UV-bright galaxies at z ≳ 10
- Predicted UVLFs are consistent with spectroscopically confirmed populations and photometrically selected candidates
- Predicted integrated UV luminosity densities agree well with observationally inferred values
- Further characterization of star formation rate variability will provide insights into early galaxy formation processes
- Bursty star formation introduces selection effects in rest-UV selected samples, raising questions about reliable cosmology constraints from high-z observations

## Summary

Recent discoveries of a significant population of bright galaxies at cosmic dawn (z ≳ 10) have provided valuable insights into cosmological galaxy formation models. One particular aspect that has been studied is the bright end of the galaxy UV luminosity function (UVLF), which appears to be higher than what many models predict. In this study, the authors use approximately 25,000 galaxy snapshots from the Feedback in Realistic Environments (FIRE) project to investigate this discrepancy. The authors find that the observed abundance of UV-bright galaxies at cosmic dawn can be reproduced in their simulations without any fine-tuning or modifications to standard stellar feedback processes. They do not need to invoke non-standard cosmology, a top-heavy stellar initial mass function, or a strongly enhanced star formation efficiency. Instead, they show that the bursty star formation histories predicted by the FIRE simulations play a crucial role in correctly reproducing the bright-end UVLFs at cosmic dawn. The authors compare the UVLFs predicted by bursty star formation in their simulations to those derived from smoothed star formation histories over prescribed timescales. They demonstrate that the strongly time-variable star formation histories induce significant changes in the abundance of UV-bright galaxies at z ≳ 10. The predicted bright-end UVLFs are consistent with both spectroscopically confirmed populations and photometrically selected candidates. Furthermore, the authors find good agreement between their predicted integrated UV luminosity densities and observationally inferred values. These densities evolve more weakly with redshift in their simulations compared to some other models. Looking ahead, further characterization of star formation rate variability on different timescales will provide insights into the physical processes involved in early galaxy formation. Bursty star formation also introduces important selection effects in rest-UV selected samples, raising questions about how high-z galaxy observations can reliably constrain cosmology. It is also of interest to explore observational methods for characterizing time variability of star formation. In conclusion, this study demonstrates that bursty star formation naturally explains the abundance of bright galaxies at cosmic dawn. The authors' simulations reproduce the observed UVLFs without needing additional modifications or fine-tuning; instead they show that bursty star formation histories play a key role in correctly reproducing observed properties of high-z galaxies.