Star formation histories (SFH) of early (6$9$, 87% of massive galaxies, (log(M_/M₎9), have SFR gradients consistent with a stochastic star-formation activity during the last 100 Myr, while this fraction drops to 15% at $z<7$. On the other hand, we see an increasing fraction of galaxies with a star-formation activity following a common stream on the SFR-M_ plane with cosmic time, indicating that a secular mode of star-formation is emerging. We place our results in the context of the observed excess of UV emission as probed by the UV luminosity function at z10, by estimating σUV, the dispersion of the UV absolute magnitude distribution, to be of the order of 1.2mag and compare it with predictions from the literature. In conclusion, we find a transition of star-formation mode happening around z~9: Galaxies with stochastic SFHs dominates at z9, although this level of stochasticity is too low to reach those invoked by recent models to reproduce the observed UV luminosity function.
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Ciesla et al. (2023) studied this question.