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We performed 3-dimensional N-body/SPH simulations to study how massresolution and other model parameters such as the star formation efficiencyparameter, C* and the threshold density, nth affect structures of the galacticgaseous/stellar disk in a static galactic potential. We employ 10^6 - 10^7particles to resolve a cold and dense (T < 100 K & n_H > 100 cm^{-3}) phase. Wefound that structures of the ISM and the distribution of young stars aresensitive to the assumed nth. High-nth models with nth = 100 cm^{-3} yieldclumpy multi-phase features in the ISM. Young stars are distributed in a thindisk of which half-mass scale height is 10 - 30 pc. In low-nth models with nth= 0.1 cm^{-3}, the stellar disk is found to be several times thicker, and thegas disk appears smoother than the high-nth models. A high-resolutionsimulation with high-nth is necessary to reproduce the complex structure of thegas disk. The global properties of the model galaxies in low-nth models, suchas star formation histories, are similar to those in the high-nth models whenwe tune the value of C* so that they reproduce the observed relation betweensurface gas density and surface star formation rate density. We howeveremphasize that high-nth models automatically reproduce the relation, regardlessof the values of C*. The ISM structure, phase distribution, and distributionsof young star forming region are quite similar between two runs with values ofC* which differ by a factor of 15. We also found that the timescale of the flowfrom n_H ~1 cm^{-3} to n_H > 100 cm^{-3} is about 5 times as long as the localdynamical time and is independent of the value of C*. The use of a high-nthcriterion for star formation in high-resolution simulations makes numericalmodels fairy insensitive to the modelling of star formation. (Abridged)

publications of the astronomical society of japan

Toward first-principle simulations of galaxy formation: I. How should we  choose star formation criteria in high-resolution simulations of disk  galaxies?