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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Abstract

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
Volume730
Issue number2
DOIs
Publication statusPublished - Apr 2011

Keywords

  • cosmology: observations
  • galaxies: evolution
  • RICH SPIRAL GALAXIES
  • DISK GALAXIES
  • CLUSTER
  • EFFICIENCY
  • TELESCOPE
  • Z=1.5
  • Z=0.4

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