| Abstract: | The cosmic evolution of the star formation rate is characterized by a peak ten billion years ago and a subsequent drop by an order of magnitude. As stars are formed from cold molecular gas, high levels of star formation are sustained by a continuous supply of fresh gas and high molecular gas fractions: the winding-down of star formation seems to be mostly driven by the diminishing cold gas reservoirs. But the star formation processes could also have been more efficient earlier in the history of the Universe. I will present the IRAM PHIBSS programs, which aim at understanding early galaxy evolution and the winding-down of star formation from the perspective of the galaxies’ molecular gas reservoirs, hence tracing the evolution of the gas fraction and of the star formation efficiency with redshift. These programs help understanding star formation within normal star-forming galaxies and their confinement within a relatively tight “main sequence” in the stellar mass/star formation rate plane. |