A decrease of the gas exchanges between galaxies and the IGM, from 12 to
  6 billion years ago
  Using a representative sample of 65 intermediate mass galaxies at z \sim 0.6,
we have inves- tigated the interplay between the main ingredients of chemical
evolution: metal abundance, gas mass, stellar mass and SFR. All quantities have
been estimated using deep spectroscopy and photometry from UV to IR and
assuming an inversion of the Schmitt-Kennicutt law for the gas fraction. Six
billion years ago, galaxies had a mean gas fraction of 32% \pm 3, i.e. twice
that of their local counterparts. Using higher redshift samples from the
literature, we explore the gas-phases and estimate the evolution of the mean
gas fraction of distant galaxies over the last 11 Gy. The gas fraction
increases linearly at the rate of 4% per Gyr from z \sim 0 to z \sim 2.2. We
also demonstrate for a statistically representative sample that < 4% of the z
\sim 0.6 galaxies are undergoing outflow events, in sharp contrast with z \sim
2.2 galaxies. The observed co-evolution of metals and gas over the past 6 Gyr
favours a scenario in which the population of intermediate mass galaxies
evolved as closed-systems, converting their own gas reservoirs into stars.
