ACTIVE GALACTIC NUCLEI AND GALAXY FORMATION

It is proposed that early jet-induced activity around active galactic nuclei (AGNs) is responsible for triggering large-scale star formation in protogalaxies and results in the formation of giant ellipticals an d spheroids in the universe. Specifically, Begelman & Cioffi's model f or overpressured cocoons expanding into protogalactic environs yields size estimates that roughly correspond to those observed in present-da y ellipticals. Within this framework, the most energetic radio jets tr igger the formation of large ellipticals, while the systems with lower jet energies are responsible for the formation of smaller spheroids a nd bulges of galaxies. Further, the evolution of AGNs with redshift al so explains the observed local density of spheroids. Such a scenario n aturally accommodates a wide variety of astrophysical observations, in cluding the origin of the infrared Hubble diagram for the most powerfu l radio galaxies, the origin of galaxy morphologies, the existence of a morphology-density relation in galaxy clusters, angular correlations of QSOs, the observed properties of the highest redshift galaxies, an d the correlation of central black hole mass with bulge luminosity in nearby galaxies.