Institution(s): 1. Observatoire de Paris
The relation between star formation and gas density appears linear for galaxies on the main sequence of star forming galaxies, and when the molecular gas is considered. However, the star formation efficiency (SFE) defined as the ratio of SFR to gas surface densities, varies as a function of type, environment, or even as a function of radius inside a galaxy. I will review recent work showing how the SFE in galaxy centers, and in the outer regions can be higher or lower than the most common value. Physical processes able to explain these observations will be discussed.