# Stress Testing $Λ$CDM with High-redshift Galaxy Candidates

**Authors:** Michael Boylan-Kolchin  
**arXiv:** [2208.01611](https://arxiv.org/abs/2208.01611)  
**Date:** 2022-08-02  
**Summary page:** https://www.summarizepaper.com/en/paper/2208.01611v1/

## Key points

- Early data from the James Webb Space Telescope (JWST) has revealed high-redshift galaxy candidates with unexpectedly high stellar masses.
- The author examines these candidates in relation to the most massive galaxies predicted by $\Lambda$CDM-like models.
- According to these models, a galaxy's stellar mass is constrained by the available baryonic reservoir of its host dark matter halo.
- However, the reported masses of the most massive galaxy candidates at $z \sim 10$ appear to be in tension with these limits.
- This suggests potential issues with photometric selection techniques, stellar mass estimation methods, survey volume estimates, or even the $\Lambda$CDM model itself.
- The tension is more pronounced at $z \sim 10" than at higher redshifts probed by JWST thus far.
- Future wider-area surveys conducted by JWST have the potential to confirm or refute this discrepancy quickly.
- If subsequent JWST data continues to reveal remarkably massive galaxies at early cosmic epochs, it would have implications for our understanding of galaxy formation and cosmology.

## Summary

The early data from the James Webb Space Telescope (JWST) has provided us with a wealth of high-redshift galaxy candidates that possess unexpectedly high stellar masses. In this study, the author examines these candidates in relation to the most massive galaxies predicted by $\Lambda$CDM-like models. These models suggest that the stellar mass of a galaxy is constrained by the available baryonic reservoir of its host dark matter halo. According to a given cosmology, the abundance of dark matter halos as a function of mass and redshift establishes an upper limit on the number density $n(>M_{\star},z)$ and stellar mass density $\rho_{\star}(>M_{\star},z)$ of galaxies above a certain stellar mass threshold $M_{\star}$ at any epoch $z$. However, the reported masses of the most massive galaxy candidates at $z \sim 10$ in JWST observations appear to be in tension with these limits. This suggests that there may be issues with well-established techniques for photometric selection of galaxies, estimation of galaxy stellar mass or effective survey volume, or even with the $\Lambda$CDM model itself. Notably, this tension is more pronounced at $z \sim 10" than at higher redshifts ($z \sim 16-20") that have been probed by JWST galaxy candidates thus far. This finding is promising for future tests of the $\Lambda$CDM model using wider-area surveys conducted by JWST. The strongest tension observed at $z \sim 10" implies that forthcoming surveys will have the potential to confirm or refute this discrepancy quickly. If subsequent JWST data continue to reveal remarkably massive galaxies at very early cosmic epochs, it would bring about exciting surprises and implications for our understanding of galaxy formation and cosmology. In terms of additional context, references are made to other studies such as Virtanen et al. (2020) and Wang et al. (2022), which provide further insights into relevant topics in the field of astrophysics. The author also mentions the work by Yan et al. (2022) and highlights that all data used in calculations and figures are available upon request, with permission required for sharing data from Labbé et al. (2022). Overall, this study sheds light on the tension between observed high-redshift galaxy candidates' masses and theoretical predictions based on $\Lambda$CDM-like models. It underscores the need for further investigation into photometric selection techniques, stellar mass estimation methods, survey volume estimates, and potentially revisiting aspects of the $\Lambda$CDM model itself to reconcile these discrepancies.