Implications of $z>{\sim}12$ JWST galaxies for galaxy formation at high redshift

TL;DR

This study uses a semi-analytic model and cosmological simulations to analyze high-redshift JWST galaxy analogues, revealing that faint galaxies align with standard models while bright candidates may require altered star formation efficiencies, indicating potential differences in early galaxy formation.

Contribution

First comprehensive simulation-based analysis of JWST high-redshift galaxy analogues, exploring their properties, environments, and implications for galaxy formation theories.

Findings

Faint JWST galaxies are consistent with standard models.

Bright galaxy analogues are rare and may need altered star formation efficiencies.

High-redshift candidates could be contaminated by low-redshift galaxies.

Abstract

Using a semi-analytic galaxy-formation model, we study analogues of 8 recently discovered JWST galaxies at $z>{\sim}12$. We select analogues from a cosmological simulation with a $(311{\rm cMpc})^3$ volume and an effective particle number of $10^{12}$ enabling resolution of every atomic-cooling galaxy at $z{\le}20$. We vary model parameters to reproduce the observed UV luminosity function at $5{<}z{<}13$, aiming for a statistically representative high-redshift galaxy mock catalogue. Using the forward-modelled JWST photometry, we identify analogues from this catalogue and study their properties as well as possible evolutionary paths and local environments. We find faint JWST galaxies ($M_{\rm UV}>{\sim}-19.5$) to remain consistent with standard galaxy-formation model and that our fiducial catalogue includes large samples of their analogues. The properties of these analogues broadly agree with conventional SED fitting results, except for having systematically lower redshifts due to the evolving UV luminosity function, and for having higher specific star formation rates as a result of burstier histories in our model. On the other hand, only a handful of bright galaxy analogues can be identified for the observed $z{\sim}12$ galaxies. Moreover, in order to reproduce the $z>{\sim}16$ JWST galaxy candidates, boosted star-forming efficiencies and reduced feedback regulation are necessary relative to models of lower-redshift populations. This suggests star formation in the first galaxies could differ significantly from their lower-redshift counterparts. We also find that these candidates are subject to low-redshift contamination, which is present in our fiducial results as both the dusty or quiescent galaxies at $z{\sim}5$.