Dynamical models for the formation and evolution of spherical galaxies

Models for the collapse of spherical protogalaxies have been computed using a two-fluid hydrodynamical approach to treat both the gas and the stars. The effects of gaseous energy losses, star formation, stellar mass loss and heavy element (Z) production are included and are followed over the lifetime of the galaxy. With reasonable choices for the parameters, the models reproduce well the observed structure of NGC 3379 and other nearly spherical galaxies. The observed Z gradients in elliptical galaxies are qualitatively reproduced, and metal-poor stars are very rare in the inner regions of the models, as in the solar vicinity. Star formation continues for the longest time in the nucleus, owing to the continuing condensation of residual gas toward the centre, and in some circumstances the infall of the last remnants of the initial protocloud may continue to support significant star formation in a galaxy even after iolO yr. Various characteristics of the models suggest that the quasar phenomenon may be identifiable with the formation of the nucleus of a giant elliptical galaxy.