On the Formation and Evolution of Disk Galaxies: Cosmological Initial Conditions and the Gravitational Collapse

We use a semianalytical approach and a CDM cosmological model to study thegravitational collapse and virialization, the structure, as well as the globaland statistical properties of isolated dark matter galactic halos which emergefrom primordial Gaussian fluctuations. From the statistical properties of thedensity fluctuation field the possible mass aggregation histories (MAHs) aregenerated, and these histories are used as the initial conditions of thegravitational collapse. To calculate the structure of the virialized systems wehave generalized the secondary infall model. Although a range of halostructures is obtained, the average density profiles agree with the profilederived as a fitting formula to results of N-body cosmological simulations. Thecomparison of the density profiles with the observational data is disscused,and some possible solutions to the disagreement found in the inner regions arediscussed. The results of our approach, after considering the gravitationaldragging of the baryon matter that forms a central disk in centrifugalequilibrium, show that the Tully-Fisher relation and its scatter can beexplained through the initial cosmological conditions. The sigma8=1 SCDM modelproduces galaxies with high velocities when compared to observations, but whenthe SCDM power spectrum is normalized to sigma8=0.57 an excellent agreementwith the observable TF relation is found, suggesting that this relation is thenatural extension to galactic scales of the observed galaxy distribution powerspectrum. The theoretical TF scatter is close to the measured one. The slope ofthe TF relation is practically invariant with respect to the spin parameterlambda.Comment: 31 pages, 7 ps figures. Accepted in ApJ. Minor corrections suggested by the refere