GALAXY FORMATION IN DARK-MATTER MODELS

The hybrid cold dark matter (CDM) plus hot dark matter (HDM) models an d the tilted CDM (n < 1) models are studied by calculating the abundan ces of normal (elliptical and spiral) galaxies and comparing the calcu lated results with the observational data. For the hybrid CDM + HDM mo dels, I present a simpler treatment for the relativistic neutrinos. Th e numerical results of density perturbation spectra given by this trea tment are in good agreement with that given by other authors for both the pure-neutrino dominated universe and the CDM + HDM universe. To ca lculate the abundances of ellipticals and spirals, I use the Press-Sch echter (1974) mass function and an analytic formalism proposed by Evra rd (1989). The numerical results show that the hybrid dark matter mode l ((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 resul ts on producing galaxies, therefore have similar power on galactic sca les as well as on large scales (for giving similar results on the anis otropies of the microwave background radiation and the large-scale pec uliar velocity field of galaxies), and galaxy formation in these two m odels 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.