A new clump-based star formation model for galaxy simulations: implications for high-redshift compact star clusters

We develop a new star formation model for galaxy simulations in which star-forming gas clumps are identified on-the-fly and converted into stars with an efficiency ε SF set by the clump surface density Σ c, calibrated against radiation hydrodynamics simulations of star cluster formation. Applying this model to isolated disc galaxies embedded in haloes of M h=10 9, 10 10 and 10 11, M, with disc compactness corresponding to redshift z=0 -- 10, we find that more compact discs form more massive and denser clumps. The maximum clump mass increases from about 10 5 to about 10 7, M, and the fraction of clumps exceeding the surface density of 300, M,pc-2 rises from 0.25 to 0.38 between z=0 and 10 in 10 10, M haloes. Star formation becomes correspondingly bursty, and the global star formation efficiency after three disc rotations increases from 5 times 10-3 to 2 times 10-1 in 10 10, M haloes and from 2 times 10-2 to 4 times 10-1 in 10 11, M haloes as the redshift increases from z=0 to 10. The accompanying feedback disrupts the gas discs of the most compact systems, while prominent stellar spiral arms emerge. Self-gravitationally bound star clusters form only in compact discs. We find no bound star clusters at z at most 2 in 10 10, M haloes, whereas the bound cluster mass fraction reaches about 40 per cent at z at least 8 and about 70 per cent in the most compact 10 11, M halo. These fractions are broadly consistent with those inferred for high- z clumpy galaxies observed by the James Webb Space Telescope.