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., ${\mathrm{\Omega }}_0=\text{ocdm}+\text{ohdm}+\text{obaryon}=1$). Primordial density fluctuation spectrum is taken to have the Zel’dovich-Harrison form. Three models are studied, with Model I having $\text{ocdm}=0.69$, $\text{obaryon}=0.01$, and $\text{ohdm}=0.30$ in one flavor of neutrinos; Model II having $\text{ocdm}=0.60$, $\text{obaryon}=0.10$, and $\text{ohdm}=0.30$ in one flavor of neutrinos; Model III having $\text{ocdm}=0.69$, $\text{obaryon}=0.01$, and $\text{ohdm}=0.30$ 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 $\text{ls}10\text{mpc}$. 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$\text{mpc}$ are frequently seen in the simulations.