Cosmological Simulations of Formation of Galaxies and Clustersand Origin of biasing

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(1) Nonlinear Stochastic Biasing in dark matter halos and high-density peaks : We quantifiesthe degree of nonlinearity and stochasticity of the clustering of biased objects, using cosmological N-body simulations. Adopting the peaks and the halos as representative biasing models, we focus on the two-point correlation of the biased objects, dark matter and their cross-correlation. Especially, we take account of the effect of redshift-space distortion and attempt to clarify the scale-dependence and the time-dependence by analyzing the biasing factor and the cross-correlation factor. On small scales, stochasticity and nonlinearity become appreciable and strongly object-dependent, especially in redshift space due to the pair-wise velocity dispersion of the biased objects. Nevertheless, an approximation of deterministic linear biasingworks reasonably well even in the quasi-linear regime, and linear redshift-space distortion explains the clustering amplitudes in redshift space in this regime. … More (2) Biasing model of galaxies and clusters on the basis of cosmological hydrodynamic simulations :We perform an extensive analysis of nonlinear and stochastic biasing of galaxies and dark halos in spatially flat low-density COM universe using cosmological hydrodynamic simulations. We compare their biasing properties with the predictions of an analytic halo biasing model. Interestingly the biasing properties of galaxies are better described by extrapolating the halo biasing model predictions. The clustering amplitudes of galaxies are almost independent of the redshift between z=0 and 3 as reported in previous simulations. We also find the clear dependence of galaxy biasing on their formation epoch ; the distribution of old populations of galaxies tightly correlates with the underlying mass density field, while that of young populations is slightly more stochastic and anti-biased relative to dark matter. The amplitude of two-point correlation function of old populations is about 3 times larger than that of the young populations. Furthermore, the old population of galaxies reside within massive dark halos while the young galaxies are preferentially formed in smaller dark halos. Assuming that the observed early and late-type galaxies correspond to the simulated old and young populations of galaxies, respectively, all of these segregations of galaxies are consistent with observational ones for the early and late-type of galaxies such as the morphology-density relation of galaxies. Less