Star formation efficiency per free-fall time (ε_ff) as a function of virial parameter (α_vir) used in the local gravo-thermo-turbulent (GTT) subgrid model. We plot ε_ff for seven different Mach numbers (ℳ) equally spaced in logarithmic intervals from 0.1 to 100. The curves for the two smallest ℳ overlap so only six curves are shown on the plot. The dotted lines indicate the region where star formation is inhibited according to Eq. (7).