PROPERTIES OF DISK GALAXIES IN A HIERARCHICAL FORMATION SCENARIO

We used galaxy evolutionary models in a hierarchical inside-out disk formation scenario to study the origin of the main local and global properties of disk galaxies as well as some of the correlations between their global properties. We found that most of disk galaxy properties and their correlations are the result of three (cosmological) initial factors of the system and their dispersions: the virial mass, the halo mass aggregation history (MAH), and the angular momentum given through the spin parameter λ. The MAH determines mainly the dark halo structure and the integral color indexes while λ determines mainly the disk surface brightness and the bulge-to-disk ratio. We calculated star formation using a gravitational instability criterion and a self-regulation mechanism driven by the energy balance in the disk turbulent interstellar medium. The efficiency of s formation in this model is almost independent from the mass of the system. Therefore, the galaxy integral color index B V or the stellar mass-to-luminosity ratio, M/LB, do not depend upon mass. We show that the luminosity-dependent dust absorption empirically determined by Wang & Heckman explains the observed color-magnitude and color Tully-Fisher (TF) relations without the necessity of introducing a massdependent star formation efficiency. The star formation history in our models is driven by both the MAH and the surface density (λ). The disks in centrifugal equilibrium form within growing cold dark matter halos with a gas accretion rate proportional to the halo MAH. The disks present exponential surface density and brightness profiles, negative radial color index gradients, and nearly flat rotation curves. We also calculated the secular formation of a bulge due to gravitational instabilities in the stellar disk. The intensive properties of our models agree very well with the observational data and they follow the same trends galaxies follow across the Hubble sequence. The infrared TF relations and the luminosity-radius relation predicted for the cosmological model used here also agree with the observational data. The main shortcomings of the inside-out hierarchical formation models presented in this paper are the excessive radial color gradients and the dark halo dominion in the rotation curve decompositions.