Comparison of molecular and atomic gas samples. Left: the ratio of molecular versus atomic gas as a function of redshift. Right: the total gas fraction ((M_HI + M_H2)/(M_* + M_HI + M_H2)) as a function of redshift. The symbols are the same as Figure 6. In both plots, the lower red symbol corresponds to the CHILES z = 0.376 detection assuming α_CO = 0.8 and the higher red symbol corresponds to the same galaxy assuming α_CO = 4.3. We have omitted the second legend for clarity. To plot the dark brown lines, we combine the “typical” H I model from 6a with the “main sequence” model for molecular gas from 6b. To plot the light brown lines, we combine the H I “gas-rich” model from Fig. 6a with the molecular gas “starburst” model from 6b. See the text for more details.