The large-scale structure in a universe dominated by cold plus hot dark matter

Using numerical simulations, we investigate the large-scale gravitational clustering in a flat universe dominated by cold plus hot dark matter (i.e., $\Omega_0=\ocdm+\ohdm+\obaryon=1$). Primordial density fluctuation spectrum is taken to have the Zel'dovich-Harrison form. Three models are studied, with Model I having $\ocdm=0.69$, $\obaryon=0.01$, and $\ohdm=0.30$ in one flavor of neutrinos; Model II having $\ocdm=0.60$, $\obaryon=0.10$, and $\ohdm=0.30$ in one flavor of neutrinos; Model III having $\ocdm=0.69$, $\obaryon=0.01$, and $\ohdm=0.30$ in three flavors of neutrinos. The initial density spectra are normalized by the COBE quadrupole measurement, and galaxies are identified from the peaks of initial density fields above a certain threshold chosen, to match the observed two-point correlation on scales $\ls 10\mpc$. Thus the clustering properties of both the mass and the galaxies are completely specified. The biasing parameter (for the `galaxies') determined in this way is $b_g\approx 1.2$ for Model I, 1.5 for Model II and 1.6 for Model III. The clustering and motions of the simulated `galaxies' are compared with recent observations. The spatial distributions of galaxies in the hybrid models are very frothy; filaments, sheets, voids etc. of sizes 10 -- 50$\mpc$ are frequently seen in the simulations.