Abstract

During the past decade many theoretical and observational activities have focused on the understanding of the negative feedback mechanisms responsible for quenching star formation in galaxies. However, recent theories have proposed that some of these mechanisms (and in particular massive outflows) can actually also boost star formation in galaxies. This would be an new mode of star formation in galaxies, which would be in addition to the “classical” star formation modes (i.e. the “quiescent” mode, in galaxy discs, and the “starburst” mode, galaxy mergers). Although this scenario is attracting growing interest, observational evidence for such “positive feedback” at work has been sparse so far. However, the elusiveness of such mechanism may simply be a consequence of observational difficulties. I will review the observational evidence of positive feedback obtained so far and I will show some new results revealing that this mechanism can actually play a major role in galaxy evolution.