Dissipative formation of an elliptical galaxy

Dissipative collapse and star formation within a protogalaxy are modeled using a simple scheme of gas cloud collisions within an N-body code. The gas physics model incorporates pressure, dissipation, and star formation, with the associated ejection of metal-enriched gas back into the cloud medium. The gas and stars collapse under their self-gravity alone; adding a static potential corresponding to a massive dark halo suppresses both velocity anisotropies and mass loss in low-mass ellipticals. A set of models in general accord with the kinematic and chemical properties of individual ellipticals is found. These models are slowly rotating and flattened by anisotropic velocity dispersions, with the radial profiles of surface density having a logarithmic gradient near -2. The chemical enrichment of the gas is calculated with a local instantaneous recycling approximation. The logarithmic abundance gradient within a massive model galaxy is -0.5, and it flattens toward zero with increasing mass loss in lower mass galaxies. The projected contours of constant metallicity are usually only slightly more flattened than the constant surface density contours. The dependence of the results on the assumed description of the gas physics is fairly small for high-mass galaxies, where the gas processes are overwhelmed by the gravitational collapse. However, lower mass model galaxies have significant pressure support during collapse which makes the results more dependent on the gas physics description