THE PROTO-GALAXY, GLOBULAR-CLUSTERS, AND QUASARS

Metallicities and horizontal-branch population gradients are used to distinguish between two populations of Galactic halo globular clusters. The beta population of clusters appears to be almost coeval and occurs mainly at R < RE.. Clusters of the beta population were probably formed during a rapid Eggen, Lynden-Bell, & Sandage (ELS)-type collapse of the inner proto-Galaxy. Clusters of the alpha population all occur at R > 8 kpc. Many of these objects are found to lie on plunging retrograde orbits. This suggests that clusters of the alpha population formed during an extended Searle-Zinn-type merger and collapse phase. The relative ages, metallicities, and locations of the alpha and beta populations indicate, as has also been suggested by Larson and by Lee, that the Galaxy formed inside out, with the dense proto-Galactic core forming stars and clusters before its lower density halo. It is very tentatively suggested that the metal-poor bulge cluster NGC 6287 might be the oldest Galactic globular cluster. In a massive galaxy the quasar phenomenon probably takes place after the bulk of its globular cluster system has formed. A quasar outburst may have guillotined cluster formation in the nearby S0 galaxy NGC 3115, thus preventing the formation of a thick-disk globular cluster population.