Galaxy Formation from a Low-Spin Density Perturbation in a CDM Universe

In order to understand the formation process of elliptical galaxies which are not rotationally supported, we carried out numerical simulations of galaxy formation from a density perturbation with a rotation corresponding to a small spin parameter. The three-dimensional TREE N-Body/SPH simulation code used included dark matter and gas dynamics, radiative cooling, star formation, supernova feedback, and metal enrichment. The initial condition was a slowly rotating, top-hat over-dense sphere on which the perturbations expected in a cold dark matter (CDM) universe were superposed. By means of a stellar-population synthesis, we calculated the surface-brightness profile, the metallicity distribution, and the photometric properties of the end-product, and found that these properties quantitatively agree with the observed properties of bright elliptical galaxies. Thus, we conclude that, in a CDM universe, a proto-galaxy having a spin-parameter as small as 0.02 evolves into an elliptical galaxy.