GALAXY FORMATION IN DARK-MATTER MODELS

The hybrid cold dark matter (CDM) plus hot dark matter (HDM) models and the tilted CDM (n < 1) models are studied by calculating the abundances of normal (elliptical and spiral) galaxies and comparing the calculated results with the observational data. For the hybrid CDM + HDM models, I present a simpler treatment for the relativistic neutrinos. The numerical results of density perturbation spectra given by this treatment are in good agreement with that given by other authors for both the pure-neutrino dominated universe and the CDM + HDM universe. To calculate the abundances of ellipticals and spirals, I use the Press-Schechter (1974) mass function and an analytic formalism proposed by Evrard (1989). The numerical results show that the hybrid dark matter model ((Omega)CDM similar or equal to 0.7, (Omega)HDM similar or equal to 0.3) and the tilted CDM model with n similar to 0.7 give similar results on producing galaxies, therefore have similar power on galactic scales as well as on large scales (for giving similar results on the anisotropies of the microwave background radiation and the large-scale peculiar velocity field of galaxies), and galaxy formation in these two models occur in a quite late epoch. On the other hand, the standard n = 1 CDM model has much stronger power to produce galaxies and the epoch of galaxy formation has to be very early, e.g. z >> 4.