On the evolution of the molecular gas fraction of star-forming galaxies

James E. Geach, Ian Smail, Sean M. Moran, Lauren A. MacArthur, Claudia del P. Lagos, Alastair C. Edge

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We present IRAM Plateau de Bure interferometric detections of CO (J = 1 -> 0) emission from a 24 mu m-selected sample of star-forming galaxies at z = 0.4. The galaxies have polycyclic aromatic hydrocarbon 7.7 mu m-derived star formation rates of SFR similar to 30-60 M-circle dot yr(-1) and stellar masses M-star similar to 10(11) M-circle dot. The CO(J = 1 -> 0) luminosities of the galaxies imply that the disks still contain a large reservoir of molecular gas, contributing similar to 20% of the baryonic mass, but have star formation "efficiencies" similar to local quiescent disks and gas-dominated disks at z similar to 1.5-2. We reveal evidence that the average molecular gas fraction has undergone strong evolution since z similar to 2, with f(gas) alpha (1 + z)(similar to 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 Lambda CDM universe are supported by these new observations.

Original languageEnglish
Article numberL19
Number of pages5
JournalAstrophysical Journal Letters
Issue number2
Publication statusPublished - Apr 2011


  • cosmology: observations
  • galaxies: evolution
  • Z=1.5
  • Z=0.4


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