We perform an extensive analysis of nonlinear and stochastic biasing of galaxies and dark halos in spatially flat low-density CDM universe ( \Omega _ { 0 } = 0.3 , \lambda _ { 0 } = 0.7 ,h = 0.7 , and \sigma _ { 8 } = 1 ) using cosmological hydrodynamic simulations .
We identify galaxies by linking cold and dense gas particles which satisfy the Jeans criterion .
We compare their biasing properties with the predictions of an analytic halo biasing model .
Dark halos in our simulations exhibit reasonable agreement with the predictions only on scales larger than \sim 10 h ^ { -1 } Mpc , and on smaller scales the volume exclusion effect of halos due to their finite size becomes substantial .
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 .
This in turn leads to a rapidly evolving biasing factor ; we find that b _ { cov } \simeq 1 at redshift z \simeq 0 to b _ { cov } \simeq 3 - 4 at z = 3 , where b _ { cov } is a biasing parameter defined from the linear regression of galaxy and dark matter density fields .
Those values are consistent with the observed clustering of Lyman-break galaxies .

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 .