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We consider the effects of different star formation criteria on galacticscales, in high-resolution simulations with explicitly resolved GMCs andstellar feedback. We compare: (1) a self-gravity criterion (based on the localvirial parameter and the assumption that self-gravitating gas collapses to highdensity in a free-fall time), (2) a fixed density threshold, (3) amolecular-gas law, (4) a temperature threshold, (5) a Jeans-instabilityrequirement, (6) a criteria that cooling times be shorter than dynamical times,and (7) a convergent-flow criterion. We consider these both MW-like andhigh-density (starburst) galaxies. With feedback present, all models produceidentical integrated star formation rates (SFRs), in agreement with theKennicutt relation. Without feedback all produce orders-of-magnitude excessiveSFRs. This is totally dependent on feedback and independent of the SF law.However, the spatial and density distribution of SF depend strongly on the SFcriteria. Because cooling rates are generally fast and gas is turbulent,criteria (4)-(7) are 'weak' and spread SF uniformly over the disk (abovedensities n~0.01-0.1 cm^-3). A molecular criterion (3) localizes to higherdensities, but still a wide range; for Z Z_solar, it is similar to a densitythreshold at n~1 cm^-3 (well below mean densities in the MW center orstarbursts). Fixed density thresholds (2) can always select the highestdensities, but must be adjusted for simulation resolution and galaxyproperties; the same threshold that works in a MW-like simulation will selectnearly all gas in a starburst. Binding criteria (1) tend to adaptively selectthe largest over-densities, independent of galaxy model or resolution, andautomatically predict clustered SF. We argue that this SF model is mostphysically-motivated and presents significant numerical advantages inlarge-dynamic range simulations.

The Meaning and Consequences of Star Formation Criteria in Galaxy Models with Resolved Stellar Feedback