Abstract

The cosmic star formation rate reveals a pronounced peak 10 Gyrs ago (or z=1-2) and then slows down, dropping by more than a factor 10 since z=1. This behaviour might be the result of combined physical processes, like hierarchical merging of galaxies, gas accretion, formation of molecular clouds and stars, metal enriched gas outflows that are driven by stellar winds, supernovae and AGN activity. I will review some IRAM recent results about the molecular content of galaxies and its dynamics, obtained from CO lines. The star formation efficiency increases with redshift, as shown by the Kennicutt-Schmidt law, and the derived depletion time. In massive galaxies, the gas fraction was higher in the past, and galaxy disks were more unstable and more turbulent. Preliminary results will be shown with ALMA , which will in the future allow the study of main sequence galaxies at high z with higher spatial resolution and sensitivity.