2011ApJ...730L..13B

We combine new sensitive, wide-field CO data from the HERACLES survey with ultraviolet and infrared data from GALEX and Spitzer to compare the surface densities of H₂, Σ_H2, and the recent star formation rate, Σ_SFR, over many thousands of positions in 30 nearby disk galaxies. We more than quadruple the size of the galaxy sample compared to previous work and include targets with a wide range of galaxy properties. Even though the disk galaxies in this study span a wide range of properties, we find a strong, and approximately linear correlation between Σ_SFR and Σ_H2 at our common resolution of 1 kpc. This implies a roughly constant median H₂ consumption time, τ^H2_Dep= Σ_H2/Σ_SFR, of ∼2.35 Gyr (including heavy elements) across our sample. At 1 kpc resolution, there is only a weak correlation between Σ_H2 and τ^H2_Depover the range Σ_H2~ 5-100 M_☉/pc2, which is probed by our data. We compile a broad set of literature measurements that have been obtained using a variety of star formation tracers, sampling schemes, and physical scales and show that overall, these data yield almost exactly the same results, although with more scatter. We interpret these results as strong, albeit indirect evidence that star formation proceeds in a uniform way in giant molecular clouds in the disks of spiral galaxies.