* Astronomy

Title: A decrease of the gas exchanges between galaxies and the IGM, from 12 to 6 billion years ago
Authors: M. Rodrigues, M. Puech, F. Hammer, B. Rothberg, H. Flores

Using a representative sample of 65 intermediate mass galaxies at z ~ 0.6, we have investigated 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% ± 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 ~ 0 to z ~ 2.2. We also demonstrate for a statistically representative sample that < 4% of the z ~ 0.6 galaxies are undergoing outflow events, in sharp contrast with z ~ 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.

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