Balancing the efficiency and stochasticity of star formation with dust extinction in z > 10 galaxies observed by JWST

TL;DR

This paper investigates how dust extinction and stochastic star formation influence the observed abundance of bright galaxies at redshifts greater than 10, using JWST data, and explores models that reconcile observations with galaxy formation theories.

Contribution

It demonstrates that stochastic star formation and dust effects can explain JWST galaxy observations, highlighting the need for efficient star formation and dust production at high redshifts.

Findings

Scatter in star formation rates boosts bright galaxy counts.

Reddening effects can reconcile models with observed galaxy properties.

Efficient dust production may be necessary in early galaxies.

Abstract

Early observations with JWST indicate an over-abundance of bright galaxies at redshifts $z \gtrsim 10$ relative to Hubble-calibrated model predictions. More puzzling still is the apparent lack of evolution in the abundance of such objects between $z \sim 9$ and the highest redshifts yet probed, $z \sim 13$-$17$. In this study, we first show that, despite a poor match with JWST LFs, semi-empirical models calibrated to UVLFs and colours at $4 \lesssim z \lesssim 8$ are largely consistent with constraints on the properties of individual JWST galaxies, including their stellar masses, ages, and rest-ultraviolet spectral slopes. We then show that order-of-magnitude scatter in the star formation rate of galaxies (at fixed halo mass) can indeed boost the abundance of bright galaxies, provided that star formation is more efficient than expected in low-mass halos. However, this solution to the abundance problem introduces tension elsewhere: because it relies on the up-scattering of low-mass halos into bright magnitude bins, one expects typical ages, masses, and spectral slopes to be much lower than constraints from galaxies observed thus far. This tension can be alleviated by non-negligible reddening, suggesting that -- if the first batch of photometrically-selected candidates are confirmed -- star formation \textit{and} dust production could be more efficient than expected in galaxies at $z \gtrsim 10$.