Eects of Starbursts on the Structure of Young Galaxies

We have investigated the e ects of primeval starbursts on the galactic structure, showing that the dynamical structure of young galaxies is changed by relaxation of a stellar system formed by a starburst-driven out owing 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 gravitational instability of a gaseous shell, we show that an expanding gaseous shell with a mass of several 10 10 M and a radius of several kpc becomes gravitationally unstable to form stars. A stellar shell is thus formed, relaxes and will evolve into a fat stellar system. In order to investigate the fate of the stellar shell and its dynamical in uence on the host galaxy, we performed three dimensional N -body simulations of a stellar shell plus disk system. The evolution of the stellar shell was computed under two types of environment: an external attened potential and a live stellar disk. We nd that the relaxation process and resultant structure are signi cantly a ected by the external disk potential, and also depend on the velocity dispersion of the initial shell stars and the mass of the shell. The nal galactic structure ranges from a thick disk and a compact bulge with a high density core to a thin disk with a di use bulge. Isodensity maps of the computed disk plus bulge system resemble isophotes of S0 galaxies. We suggest that the e ects of primeval starbursts would explain some observational properties of S0 galaxies.