Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2011-02-17
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
Accepted for publication in ApJ Letters; 5 pages, 2 figures
Scientific paper
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.
Edge Alastair C.
Geach James E.
Lagos Claudia del P.
MacArthur Lauren A.
Moran Sean M.
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