Galactic-scale outflows (or winds) are powered by stellar and/or supermassive black-hole (SMBH) accretion processes which inject energy and momentum into the interstellar medium (ISM). On a grand scale, winds may significantly affect the assembly and evolution of galaxies. Outflows are ubiquitous at any redshift and they are invoked to help explain a number of observations in the Universe.
For example, they help explain some of the observable properties of galaxies (e.g. color and gas abundance; for example, red, gas-poor ellipticals) and of the intergalactic medium (IGM). Outflows can account for the correlations that exist between the physical properties of a galaxy (e.g. the tight correlation between the SMBH mass and the mass of the spheroidal bulge). Moreover, outflows may help reconcile (or mitigate) the discrepancies between predictions from cosmological simulations and models with actual observations.