Active Galactic Nuclei and Galaxy Formation

Abstract

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 and spheroids in the universe. Specifically, Begelman & Cioffi's model for overpressured cocoons expanding into protogalactic environs yields size estimates that roughly correspond to those observed in present-day ellipticals. Within this framework, the most energetic radio jets trigger the formation of large ellipticals, while the systems with lower jet energies are responsible for the formation of smaller spheroids and bulges of galaxies. Further, the evolution of AGNs with redshift also explains the observed local density of spheroids. Such a scenario naturally accommodates a wide variety of astrophysical observations, including the origin of the infrared Hubble diagram for the most powerful 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, and the correlation of central black hole mass with bulge luminosity in nearby galaxies.