We analyze high-resolution hydrodynamics simulations of an isolated disk dwarf galaxy with an explicit model for unresolved turbulence and turbulence-based star formation prescription. We examine the characteristic values of the star formation efficiency per free-fall time, εff, and its variations with local environment properties, such as metallicity, UV flux, and surface density. We show that the star formation efficiency per free-fall time in ≈ 10 pc star-forming regions of the simulated disks has values in the range εff≈ 0.01-0.1, similar to observational estimates, with no trend with metallicity and only a weak trend with the UV flux. Likewise, εff estimated using projected patches of 500 pc size does not vary with metallicity and shows only a weak trend with average UV flux and gas surface density. The characteristic values of εff≈ 0.01-0.1 arise naturally in the simulations via the combined effect of dynamical gas compression and ensuing stellar feedback that injects thermal and turbulent energy. The compression and feedback regulate the virial parameter, αᵥir, in star-forming regions, limiting it to αᵥir≈ 3-10. Turbulence plays an important role in the universality of εff because turbulent energy and its dissipation are not sensitive to metallicity and UV flux that affect thermal energy. Our results indicate that the universality of observational estimates of εff can be plausibly explained by the turbulence-driven and feedback-regulated properties of star-forming regions.
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Polzin et al. (2024) studied this question.
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