The role of starbursts in the formation of galaxies and active galactic nuclei

Starbursts are episodes of intense star formation in the central regions of galaxies, and are the sites of ca.25% of the high–mass star formation in the local Universe. In this contribution, I review the role that starbursts play in the formation and evolution of galaxies, the intergalactic medium (IGM), and active galactic nuclei. First, I point out the empirical similarities between local starbursts and the Lyman–break population at high redshift, and emphasize the implied similarities in their basic physical, dynamical and chemical properties. In the local Universe, more–massive galaxies host more–luminous, more–metal–rich, and dustier (IR–dominated) starbursts. This underscores the need for a pan–chromatic approach to documenting and understanding the cosmic history of star formation. Second, I review the systematic properties of starburst–driven galactic superwinds. These drive metal–rich dusty gas outward at a typical velocity of 400–800 km s-1 (independent of the galaxy rotation speed) and at several times the star–formation rate. They can be directly observed both in local starbursts and high–redshift galaxies. They are probably responsible for establishing the strong mass–metallicity relation in spheroids, and for the metal–enrichment and (pre)heating of the IGM. They may have also ejected cosmologically significant amounts of intergalactic dust. Third, I discuss UV observations of the nuclei of type 2 Seyfert galaxies. These show that compact (on a scale of a few hundred pc) heavily reddened starbursts are the source of most of the ‘featureless continuum’ in UV–bright Seyfert 2 nuclei, and are an energetically significant component in these objects. Finally, I discuss the evolution of the host galaxies of radio–quiet quasars. Rest-frame optical images imply that the hosts at z ∽ 2 are only as luminous as present–day L* galaxies, less massive than the hosts of similarly luminous low–z quasars, similar to the Lyman–break galaxies, and much less luminous than powerful radio galaxies at the same redshift. These results are consistent with the idea of hierarchical galaxy assembly, and suggest that super-massive black holes may be formed/fed before their host galaxy is fully assembled.