Models for the Formation of Elliptical Galaxies

Previous models for the formation and evolution of spherical galaxies are here generalized to the case of axisymmetric rotating systems. It is found that a completely inviscid collapse does not yield a realistic model, but if a plausible turbulent viscosity is assumed it produces significant outward transfer of angular momentum during the collapse and leads to models which closely resemble elliptical galaxies. The radial structure of these models is similar to that of the spherical models, but the rotating models also predict isophotal shapes, ellipticity profiles, and rotation curves that are in qualitative agreement with observations. The distributions of metal abundance, rotational velocity, and velocity dispersion are all flattened toward the equatorial plane, and reflect a stellar population gradient perpendicular to this plane which is qualitatively similar to the stellar population gradient observed in our galaxy. If there is not too much viscosity present during the later stages of the collapse, the residual gas forms a distinct flat ‘ incipient disc ’ component.