Redshift evolution of stellar mass versus gas fraction relation in 0 < z < 2 regime: observational constraint for galaxy formation models

We investigate the redshift evolution of molecular gas mass fraction ( $f_{\rm mol} = \frac{M_{\rm mol}}{M_\star +M_{\rm mol}}$ , where M mol is molecular gas mass and M ⋆ is stellar mass) of galaxies in the redshift range of 0 < z < 2 as a function of the stellar mass by combining carbon monoxide (CO) literature data. We observe a stellar-mass dependence of the f mol evolution where massive galaxies have largely depleted their molecular gas at z = 1, whereas the f mol value of less massive galaxies drastically decreases from z = 1. We compare the observed M ⋆ − f mol relation with theoretical predictions from cosmological hydrodynamic simulations and semi-analytical models for galaxy formation. Although the theoretical studies approximately reproduce the observed mass dependence of the f mol evolution, they tend to underestimate the f mol values, particularly of less massive (1011 M⊙) when compared with the observational values. Our result suggests the importance of the feedback models which suppress the star formation while simultaneously preserving the molecular gas in order to reproduce the observed M ⋆ − f mol relation.