Galaxy formation in a CDM+Lambda universe .2. Spatial distribution of gas and galaxies

The spatial distributions of dark matter, intergalactic gas, and galaxies are studied in the framework of the CDM + Lambda cosmological model. The new code, based on the softened Lagrangian hydrodynamics approach to cosmological fluid dynamics, incorporates the dark matter and gas evolution, radiative processes in the gas and the evolution of the radiation field, and the process of galaxy formation in the quasi-Lagrangian description. The simulation utilized in this paper has 64 h(-1) Mpc box size and the softening length of 100 h(-1) kpc, thus achieving a formal dynamical range of 640. The overdensity delta of galaxies in the simulation is found to be systematically higher than that of the mass in the high-density regions and systematically lower than that of the mass in the low-density regions; this property correlates with galaxy age: the overdensity in old galaxies is higher, and the overdensity in young galaxies is lower, with respect to the mass. The spatial bias (i.e., the square root of the ratio of the galaxy power spectrum to that of the mass) is increasing toward small scales and flattens out at large scales; the variation of the bias factor with galaxy age is significant, with young galaxies tracing the mass and old galaxies biased (in a sense of the power spectrum) with a bias factor up to 10 at the cluster scale. The precise comparison of simulations with observations is therefore strongly affected by selection effects because even a small variation in M/L can produce significant variations in the spatial bias factor. The correlation function for all galaxies deviates from the Davis & Peebles (1983) law on scales smaller than 3 h(-1) Mpc, but the correlation function for the youngest mass quartile fits the observed IRAS correlation function extremely well up to the scales of 400 h(-1) kpc.