The determination of the star formation rate of galaxies suffers from strong uncertainties mainly due to dust obscuration and AGN contamination. With Herschel, it is now possible to determine with unprecedented accuracy the actual SFR of distant galaxies and make a major step forward in the understanding of the dominant factors playing a role in the building of present-day galaxies. We will review the latest results obtained with the deepest far-infrared imaging of the deep Universe in the GOODS fields with the Herschel observatory, in the framework of the GOODS-Herschel key project.

Most present-day stars were formed at intermediate redshifts around z=0.5-2.5. This is also the epoch when the cosmic star formation history peaked and started to decline until present-day. The cause of this decline has been a major theme of debate and various physical mechanisms have been invoked to explain it ranging from a drop of the rate of mergers to the quenching of star formation from AGN feedback or simply the exhaustion of the gas content of galaxies. Imaging with HST of the dominant galaxy population at these redshifts revealed the presence of large clumps of star formation suggesting that the gas reservoirs participating to these major events of star formation were subject to strong dynamical instabilities. These instabilities could either result from major mergers of galaxies or be driven by intergalactic infall of material through filaments, the so-called cold flows.

We will present evidence that galaxies formed their stars following some scaling laws. While there are many reasons to believe that the physics of galaxy/star formation is a complex process involving turbulence, multiphase physics, magnetic fields, shocks, mergers, environment effects, positive/negative feedback, these scaling laws instead suggest that gravity leads the growth of galaxies in stars and black hole growth and that the role of mergers in this process has been overstated.