EFFECTS OF STARBURSTS ON THE STRUCTURE OF YOUNG GALAXIES

We have investigated the effects of primeval starbursts on the galacti c structure, showing that the dynamical structure of young galaxies is changed by the relaxation of a stellar system formed by a starburst-d riven outflowing gas (superwind). When a superwind interacts with halo gas, an expanding dense supershell of shocked gas is formed. Using a similarity solution for the expanding shell and a condition for the gr avitational instability of a gaseous shell, we show that an expanding gaseous shell with a mass of several 10(10)M(.) and a radius of severa l kpc becomes gravitationally unstable to form stars. A stellar shell is thus formed, relaxes, and evolves into a fat stellar system. In ord er to investigate the fate of the stellar shell and its dynamical infl uence on the host galaxy, we performed three-dimensional N-body simula tions of a stellar shell plus a disk system. The evolution of the stel lar shell was computed under two types of environment: an external fla ttened potential and a live stellar disk. We found that the relaxation process and the resultant structure are significantly affected by the external disk potential, and also depend on the velocity dispersion o f the initial shell stars and the mass of the shell. The final galacti c structure ranges from a thick disk and a compact bulge with a high-d ensity core to a thin disk with a diffused bulge. The effects of prime val starbursts would explain some of the observational properties of S 0 galaxies.