Upper left panel: molecular fraction as a function of stellar surface density. Upper right panel: molecular fraction as a function of the total gas surface density. Lower left panel: total gas as a function of molecular fraction divided by ISM pressure. Lower right: pressure due to the gravitational potential of the gas divided by the pressure due to the potential of the stellar disk (P_g/P_s) as a function of the molecular fraction divided by ISM pressure. Typical errors bars are given for each relation.