2010ApJ...710L..88T

We use observations of the radial profiles of the mass surface density of total, Σ_g, and molecular, Σ_H2, gas rotation velocity and star formation rate surface density, Σ_sfr, of the molecular dominated regions of 12 disk galaxies from Leroy et al. to test several star formation laws: a "Kennicutt-Schmidt power law," Σ_sfr= A_gΣ^1.5_ g,2_; a "constant molecular law," Σ_sfr= A_H2Σ_H2,2; the "turbulence-regulated laws" of Krumholz & McKee (KM) and Krumholz, McKee, & Tumlinson (KMT), a "gas-Ω law," Σ_sfr= B_ΩΣ_ g_Ω; and a shear-driven "giant molecular cloud (GMC) collisions law," Σ_sfr= B_CCΣ_gΩ(1 - 0.7β), where β ≡ d ln v_circ/d ln r. We find the constant molecular law, KMT turbulence law, and GMC collision law are the most accurate, with an rms error of a factor of 1.5 if the normalization constants are allowed to vary between galaxies. Of these three laws, the GMC collision law does not require a change in physics to account for the full range of star formation activity seen from normal galaxies to circumnuclear starbursts. A single global GMC collision law with B_CC= 8.0x10^–3, i.e., a gas consumption time of 20 orbital times for β = 0, yields an rms error of a factor of 1.8.