A Galaxy Formation Cookbook: Recipes and Utensils.
Abstract
New numerical simulations of hierarchical galaxy formation including gas dynamics are presented. These simulations are conducted using a new, generalpurpose program for evolving selfgravitating systems in three dimensions. The gravitational forces are calculated using a hierarchical tree algorithm while the gas dynamic properties are determined using smoothed particle hydrodynamics. Since in this method the complete thermodynamic state of the gas is known everywhere, dissipational effects can be included by allowing the gas to cool radiatively, using standard cooling curves, and star formation can be prescribed in a physical manner. The simulations model the collapse of isolated constant density perturbations, made of dark and baryonic matter in a 10 to 1 ratio, initially in solid rotation and in Hubble flow. Small scale power is added using the Zel'dovich approximation assuming a power law slope of either 2.5 or 0. The simulations are successful in making systems that resemble spirals and ellipticals. Of the parameters that are investigated the small scale power amplitude, the initial angular momentum, and the star formation rateit is the amplitude of the small scale power that is most important in determining the final Hubble type. Systems form through the merger of subclumps. The systems with larger small scale power have clumps with higher central densities. Higher density clumps retain their identities longer than low density clumps and are able to lose more angular momentum. These systems form ellipticals. Spirals form when these clumps are not very distinct and little angular momentum transport occurs. Since the Hubble type is determined by how much small scale power is present when compared to the height of the galaxysized peak, the densitymorphology relation is easily explained. The formation and equilibrium characteristics of systems formed through dissipationless collapse using similar initial conditions are also studied. The final equilibrium systems approximately follow a de Vaucouleurs R^{1/4} law, are slowly rotating with a measured flat rotation curve, and are supported by an anisotropic velocity dispersion. They closely resemble elliptical galaxies suggesting that elliptical galaxies could form through dissipationless collapse. These models could also represent the formation of galactic haloes.
 Publication:

Ph.D. Thesis
 Pub Date:
 1989
 Bibcode:
 1989PhDT.........7K
 Keywords:

 Physics: Astronomy and Astrophysics;
 Astronomical Models;
 Computerized Simulation;
 Dynamic Characteristics;
 Galactic Evolution;
 Galaxies;
 Gas Dynamics;
 Hydrodynamics;
 Thermodynamics;
 Algorithms;
 Cooling;
 Dark Matter;
 Gravitational Fields;
 Momentum Transfer;
 Perturbation;
 Star Formation;
 Star Formation Rate;
 Trees (Mathematics);
 Astrophysics