  To understand the impact of star formation models on galaxy evolution, we
perform cosmological zoom-in radiation-hydrodynamic simulations of a dwarf dark
matter halo with virial mass 1e9 Msun at z=6. Two different star formation
models are compared, a model based on a local gravo-thermo-turbulent condition
and a model based on a sink particle algorithm. Using idealized tests of
collapsing isothermal spheres and giant molecular clouds with different
turbulent structures, we determine the optimal accretion radius to be twice the
cell size and the resolution required to achieve reasonable convergence in star
formation efficiency to 0.3 pc for the sink algorithm. As a first study in this
series, we use cosmological zoom-in simulations with different spatial
resolutions and find that star formation is more bursty in the runs with the
sink algorithm, generating stronger outflows than in the runs with the
gravo-thermo-turbulent model. The main reason for the increased burstiness is
that the gas accretion rates on the sinks are high enough to form stars on very
short timescales, leading to more clustered star formation. As a result, the
star-forming clumps are disrupted more quickly in the sink run due to more
coherent radiation and supernova feedback. The difference in burstiness between
the two star formation models becomes even more pronounced when the supernova
explosion energy is artificially increased. Our results suggest that improving
the modelling of star formation on small, sub-molecular cloud scales can
significantly impact the global properties of simulated galaxies.
