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 the molecular gas mass fraction
(f_mol=M_mol/(M_star+M_mol), where M_mol is molecular gas mass and M_star is
stellar mass) of galaxies in the redshift range of 0<z<2 as a function of the
stellar mass by combining 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_star-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 f_mol evolution, they
tend to underestimate the f_mol values, particularly of less massive (<10^10
Msun) and massive galaxies (>10^11 Msun) 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_star-f_mol relation.
