# Are the ultra-high-redshift galaxies at z > 10 surprising in the context of standard galaxy formation models?

**Authors:** L. Y. Aaron Yung, Rachel S. Somerville, Steven L. Finkelstein, Stephen M. Wilkins, Jonathan P. Gardner  
**arXiv:** [2304.04348](https://arxiv.org/abs/2304.04348)  
**Date:** 2023-04-10  
**Summary page:** https://www.summarizepaper.com/en/paper/2304.04348v2/

## Key points

- Yung et al. study ultra-high redshift galaxies with redshifts greater than 10 using the James Webb Space Telescope (JWST).
- They utilize Santa Cruz semi-analytic models and GUREFT suite of cosmological N-body simulations to compare observational findings with current galaxy formation models.
- The dust-free models predict significantly lower galaxy number densities at z~11 and z~13 compared to observational estimates, with discrepancies of an order of magnitude and a factor of ~30 respectively.
- Uncertainties in observed number densities due to cosmic variance are estimated to range from ~20-30% at z=11 to ~30-80% at z=14 for a 100 sq arcmin field.
- Stellar-driven winds are identified as the primary limiting factor for the formation of luminous galaxies during these early epochs.
- Introducing a modest boost to UV luminosities or incorporating a stochastic component is suggested to better align model predictions with observational data.
- The study highlights challenges and discrepancies in modeling ultra-high redshift galaxies, offering potential avenues for refining existing galaxy formation models.

## Summary

In their study, Yung et al. investigate the presence of ultra-high redshift galaxies with redshifts greater than 10, as detected by the James Webb Space Telescope (JWST). They aim to determine whether these observational findings align with current galaxy formation models. Utilizing the Santa Cruz semi-analytic models integrated within merger trees from the GUREFT suite of cosmological N-body simulations specifically designed for ultra-high redshift studies, the researchers present predictions for stellar mass functions, rest-frame UV luminosity functions, and various scaling relations based on their fiducial models calibrated at z=0. <kf>Keywords: ultra-high redshift galaxies, James Webb Space Telescope (JWST), Santa Cruz semi-analytic models, GUREFT suite of cosmological N-body simulations, galaxy formation models.</kf>

The results indicate that their dust-free models predict significantly lower galaxy number densities at z~11 and z~13 compared to observational estimates, with a discrepancy of an order of magnitude and a factor of ~30 respectively. To account for uncertainties in observed number densities due to cosmic variance, they estimate a fractional error ranging from ~20-30% at z=11 to ~30-80% at z=14 for a 100 sq arcmin field. Through an exploration of various processes in their models such as halo formation rate, gas cooling, star formation, and stellar feedback mechanisms, the researchers identify efficient stellar-driven winds as the primary limiting factor for the formation of luminous galaxies during these early epochs. They suggest that introducing a modest boost of approximately four times to UV luminosities - possibly stemming from a top-heavy stellar initial mass function - could bring their current models into better alignment with observational data. Additionally, incorporating a stochastic component to UV luminosity is proposed as another potential method to reconcile model predictions with observational results. Overall, this study sheds light on the challenges and discrepancies in modeling ultra-high redshift galaxies and highlights potential avenues for refining existing galaxy formation models to better match observations at these extreme cosmic epochs.