The Relationship between Gas Content and Star Formation in Molecule‐rich Spiral Galaxies

We investigate the relationship between HI, H_2, and the star formation rate (SFR) using azimuthally averaged data for seven CO-bright spiral galaxies. Contrary to some earlier studies based on global fluxes, we find that the SFR surface density exhibits a much stronger correlation with the H_2 than with the HI, as the HI surface density saturates at a value of $\\sim$10 Msol pc^{-2} or even declines at large SFR surface densities. Hence the good correlation between the SFR surface density and the total (HI+H_2) gas surface density is driven by the molecular component in these galaxies. We find no clear evidence for a link between the gravitational instability parameter for the gas disk (Q_g) and the SFR, and…