Molecular gas reservoirs during the winding-down of star formation

Star formation in the Universe decreased by an order of magnitude in the last ten billion years. As stars are formed within giant molecular clouds, it is crucial to probe molecular gas reservoirs to understand this winding-down of star formation. The PHIBSS2 legacy program at the IRAM NOEMA interferometer surveys the molecular gas properties of galaxies on and around the main sequence, where most of star formation occurs. At z=0.5-0.8, we observe the CO(2-1) line for 61 targets, from which we determine molecular gas masses, gas fractions and depletion times. We separately obtain disk sizes and bulge-to-total luminosity ratios, which enable us to characterize morphological changes. Our results suggest an ongoing supply of gas to compensate for star formation and a contribution of disk stars to the growing bulge. The relation between molecular gas and star formation rate surface densities is strikingly linear, which argues in favor of uniform star formation processes across cosmic time.