2012ApJ...745..183R

We present an analysis of the relationship between molecular gas and current star formation rate surface density at sub-kiloparsec and kiloparsec scales in a sample of 14 nearby star-forming galaxies. Measuring the relationship in the bright, high molecular gas surface density (Σ_H2 ≳20 M_☉/pc2) regions of the disks to minimize the contribution from diffuse extended emission, we find an approximately linear relation between molecular gas and star formation rate surface density, N_mol∼ 0.96±0.16, with a molecular gas depletion time, τ^mol_dep∼ 2.30±1.32 Gyr. We show that in the molecular regions of our galaxies there are no clear correlations between τ^mol_dep and the free-fall and effective Jeans dynamical times throughout the sample. We do not find strong trends in the power-law index of the spatially resolved molecular gas star formation law or the molecular gas depletion time across the range of galactic stellar masses sampled (M_*∼ 10^9.7-10^11.5 M _☉). There is a trend, however, in global measurements that is particularly marked for low-mass galaxies. We suggest that this trend is probably due to the low surface brightness CO J = 1-0, and it is likely associated with changes in CO-to-H₂ conversion factor.