Abstract We introduce an effective framework to model star-formation burstiness and use it to jointly fit galaxy UV luminosity functions (UVLFs), clustering, and Hα/UV ratios, providing the first robust empirical evidence that early galaxies hosted in lower-mass halos are burstier. Using z ~ 4 − 6 observations, we find that galaxies show approximately 0. 6 dex of SFR variability if hosted in halos of Mh = 1011 M⊙ (typical of MUV ≈ −19 galaxies at z = 6). This translates into a scatter of ₌_ ₔₕ 0. 75 mag in the UVLF, in line with past findings. Strikingly, we find that burstiness grows for galaxies hosted in smaller halos, reaching ≳ 1 dex for Mh ≤ 109 M⊙ (corresponding to ₌_ ₔₕ 1. 5 mag for faint MUV ≳ −15 galaxies). Extrapolating to higher redshifts, when small halos were more prevalent, the inferred mass-dependent burstiness can reproduce observed UVLFs up to z ~ 17 within 1σ, potentially alleviating the tension between pre- and post-JWST galaxy-formation models. Current observations allow us to constrain the main burst timescale to approximately 20 Myr, consistent with expectations from supernova feedback, and suggest broad distributions of ionizing efficiencies at fixed MUV. Our results demonstrate that mass-dependent burstiness, as predicted by hydrodynamical simulations, is critical for understanding the mass assembly of early galaxies.
Muñoz et al. (Wed,) studied this question.