Abstract
We present IRAM Plateau de Bure interferometric detections of CO(1-0)
emission from a 24um-selected sample of star-forming galaxies at z=0.4. The
galaxies have PAH 7.7um-derived star formation rates of SFR~30-60 M_Sun/yr and
stellar masses M*~10^11 M_Sun. The CO(1-0) luminosities of the galaxies imply
that the disks still contain a large reservoir of molecular gas, contributing
~20% of the baryonic mass, but have star-formation 'efficiencies' similar to
local quiescent disks and gas-dominated disks at z~1.5-2. We reveal evidence
that the average molecular gas fraction has undergone strong evolution since
z~2, with f_gas ~ (1+z)^2 +/- 0.5. The evolution of f_gas encodes fundamental
information about the relative depletion/replenishment of molecular fuel in
galaxies, and is expected to be a strong function of halo mass. We show that
the latest predictions for the evolution of the molecular gas fraction in
semi-analytic models of galaxy formation within a LCDM Universe are supported
by these new observations.
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