Identification of a transition from stochastic to secular star formation around z=9 with JWST

Abstract

tar 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% atz < 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 z ≳ 10, by estimating σUV , the dispersion of the UVabsolute magnitude distribution, to be of the order of 1.2 mag 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 z ≳ 9, although this level of stochasticity is too low to reach those invoked by recent models to reproduce the observed UV luminosity function