Star-formation rate surface density as a function of H₂ (left) and Hi+H₂ (right) gas surface densities. Black dots showsubsample I and gray dots showsubsample II. The black dashed lines show the fits to the H₂ and H₂ +Hi SK law by Leroy et al. (2005) and Shi et al. (2011), respectively. Red lines indicate constant star-formation efficiencies (depletion timescales). Large arrows indicate the shift in H₂ surface density by assuming a CO-to-H₂ conversion factor 10 times larger than that of the Milky Way for the molecular mass. Error bars indicate typical uncertainties for our sample.