On Formation of Disk Galaxies from Spherical Primordial Fluctuations

Abstract

The spherical gravitational collapse and virialization of arbitrary density fluctuations in an expanding universe is studied. In the context of the standard cosmological model and the peak $ansatz$, disk galaxies are supposed to be the product of "extended" gravitational collapses of regions surrounding local-maxima of the density fluctuation field. The substructure over the main profile (merging) is considered as a second-order phenomenon. The range and distribution of possible mass growth histories or accretion regimes for a given present-day mass are estimated and used as the initial condition for galaxy formation. Considering the effect of dark halo contraction due to disk formation, the final rotation curves are calculated. If the structural properties of dark halos are important in establishing the Hubble sequence's properties of visible galaxies, then this sequence is defined not only by the mass, but among other possible parameters, by the accretion regime.