Cold plus hot dark matter and structure formation of the universe

Abstract

Cold plus hot (neutrino) dark matter models are studied and compared with the tilted cold dark matter models (which have a non-Zel'dovich initial density perturbation spectrum). For the hybrid dark matter models, a simpler treatment for the relativistic neutrinos is presented. The numerical results of this treatment are shown to be in good agreement with those given by other authors. Comparing the theoretical and the observational results of the quadrupole fluctuations of the cosmic background radiation and the large-scale velocity field of galaxies, the hybrid dark matter models require a fraction of neutrino density Ων ≃ 0.3, a fraction of cold dark matter Ωc ≃ 0.7 and a number of massive neutrino speciesNν = 1 for the case of Hubble's constantH0 = 50 km s−1 Mpc−1. The distribution of comoving number density of quasars at high redshifts is studied using the Press-Schechter theory. The calculations show that the hybrid dark matter model (Ωc ≃ 0.7, Ων ≃ 0.3) and the tilted CDM model withn = 0.7 ∼ 0.8 both account for the observed quasar abundance at high redshift.