Stochastic star formation in early galaxies: Implications for the James Webb Space Telescope

Contact. The star formation rate (SFR) in high-redshift galaxies is expected due to competing physical processes. This stochastic variability might boost the luminosity of galaxies and might explain the over-abundance seen at z >= 10 by the James Webb Space Telescope. Aims. We quantify the amplitude and timescales of this variability and identify the key physical processes. Methods. We selected 245 z = 7:7 galaxies with stellar mass 5 x 10(6). M-star/M-circle dot <= 5 x 10(10) from serra, which is a suite of high-resolution radiation-hydrodynamic cosmological simulations. After fitting the average SFR trend, < SFR > , we quantified the time-dependent variation, delta(t) log[SFR/< SFR >]; for each system and performed a periodogram analysis to search for periodicity modulations. Results. We find that delta(t) is distributed as a zero-mean Gaussian, with standard deviation sigma delta similar or equal to 0:24 (corresponding to a UV magnitude s.d. sigma(UV) similar or equal to 0:61) that is independent of M-star. However, the modulation timescale increases with stellar mass: t(delta) similar to (9; 50; 100) Myr for M-star similar to (0:1; 1; 5) x 10(9) M (circle dot), respectively. These timescales are imprinted on the SFR by di fferent processes: (i) photoevaporation, (ii) supernova explosions, and (iii) cosmological accretion /merging dominating in low-, intermediate-, and high-mass systems, respectively. Conclusions. The predicted SFR variations cannot account for the required z >= 10 UV luminosity function boost. Other processes, such as radiation-driven outflows clearing the dust, must then be invoked to explain the enhanced luminosity of super-early systems.

Automated summary

This study quantifies and analyzes the star formation rate in high-redshift galaxies, finding that it exhibits stochastic variability. This variability is related to stellar mass but cannot explain the over-abundance seen in high-redshift systems. Other physical processes, such as radiation-driven outflows, need to be invoked to explain the enhanced luminosity of super-early systems.