Galaxies at z > 10: {\Lambda}CDM predicts increased Star Formation Efficiency

TL;DR

This study demonstrates that the properties of high-redshift galaxies (z > 7) observed by JWST can be explained within the {b1}CDM model using the UniverseMachine framework, showing increased star formation efficiency at early times.

Contribution

The paper shows that the {b1}CDM model with UniverseMachine reproduces observed galaxy properties at z > 7, including UV luminosity functions and star formation rates, with a novel prediction of increasing efficiency.

Findings

UV luminosity functions match observations over five magnitudes.

Star-formation efficiency increases with redshift, reaching 2-3% by z=10-12.

Good agreement with JWST/HST galaxy stellar mass and SFR relations.

Abstract

We show that the rest-frame UV statistics and global properties of galaxies at 7 <= z <= 14 are naturally reproduced within the standard {\Lambda}CDM framework when galaxy formation is modeled with UniverseMachine applied to the high-resolution Uchuu N-body simulation. Our model matches the UV luminosity functions over five magnitudes and reproduces the evolution of the UV (and inferred star formation rate) density once internal dust attenuation is included. Comparisons with spectroscopically confirmed JWST/HST galaxies show good agreement with the stellar mass-SFR and stellar mass-UV luminosity relations. In contrast, earlier claims of insufficient stellar masses at z=8 are inconsistent with our model and are likely driven by systematic uncertainties, including AGN contamination, dust attenuation, and the lack of JWST/MIRI constraints. A key prediction is that the star-formation efficiency increases with redshift at fixed halo mass, reaching 2-3 percent of baryons converted into stars by z=10-12. These results demonstrate that current JWST observations of early galaxy populations can be explained within the {\Lambda}CDM framework.