mitigating the overcooling problem with sink-based bursty star formation in a high-z dwarf galaxy

Abstract

Star formation is a fundamental driver of galaxy evolution, yet many galaxy formation models still fail to regulate it realistically, allowing gas to collapse too efficiently and overproduce stars. To investigate a possible solution to this overcooling problem, we perform cosmological zoom-in radiation-hydrodynamics simulations of a dark matter halo reaching $10^{10} M_\odot$ at $z=6$, adopting two distinct star formation models: a Schmidt-type model, in which star formation criteria and efficiency per free-fall time are tied to local gravo-thermo-turbulent conditions, and a sink-based model, in which star formation is governed by local gas inflows. The sink-based model naturally produces bursty star formation through rapid accretion onto young sink particles embedded in strongly convergent gas flows. The resulting intense radiation ionizes and disperses star-forming clumps through photoionization heating before the first supernova explodes. Consequently, supernovae occur in lower-density environments, imparting greater terminal momentum and driving stronger galactic outflows. In contrast, star formation within individual gas clumps is less efficient in the Schmidt-type model, because individual star formation events locally modify cell conditions, temporarily suppressing subsequent star formation and lowering the degree of burstiness. Relative to the Schmidt-type model, the sink-based model yields a total stellar mass lower by a factor of $\sim3$ and a Lyman continuum escape fraction higher by a factor of $\sim10$ by $z=6$. The bursty model drives stronger metal-enriched outflows and suppresses excess central star formation, exhibiting better agreement with JWST observations in gas-phase metallicity and galaxy size. Our results suggest that bursty star formation is a key mechanism for enhancing feedback and alleviating the overcooling problem in galaxy formation simulations.