EVOLUTION OF A CLOUDY PROTOGALAXY INTERACTING WITH AN EARLY GALACTIC WIND AND GALAXY FORMATION

We argue that a combined evidence from galactic and extragalactic studies suggests that a major star formation in giant galaxies is preceded by an evolutionary phase at which a strong galactic wind driven by the initial burst of star formation enriches the gaseous protogalaxy with metals and heats it up, so that the latter turns over from contraction to expansion. The result is the ejection of enriched material from the outer part of the protogalaxy into the intergalactic space, while the inner part, after a delay of about one to a few Gyr, finally contracts and cools down to form the galactic major stellar component (the 'hot' model of galaxy formation). The paper presents a specific mechanism to produce a hot protogalaxy according to which an early galactic wind is imparting energy and momentum into a collapsing protogalaxy whose mass is contained mainly in clouds and only a small portion is in the intercloud gas that provides pressure confinement for the clouds. The model is then capable of accounting for the nearly equal mass and iron abundance in cluster giant galaxies and the intracluster gas provided the observationally plausible input parameters for giant galaxies and early galactic winds are adopted. It also predicts the formation of long-lived X-ray coronae with characteristics similar to those observed around giant ellipticals. The model specifies a characteristic length-scale that can be very naturally interpreted as a size for a stellar system to come; a very encouraging result is that it perfectly fits in with a typical size of giant ellipticals.