Simulations of galaxy formation in a cosmological volume

We present results of large N-body-hydrodynamic simulations of galaxy formation. Our simulations follow the formation of galaxies in cubic volumes of side 100 Mpc, in two versions of the cold dark matter (CDM) cosmogony: the standard, Ω = 1 SCDM model and the flat, Ω = 0.3ΛCDM model. Over 2000 galaxies form in each of these simulations. We examine the rate at which gas cools and condenses into dark matter haloes. This roughly tracks the cosmic star formation rate inferred from observations at various redshifts. Galaxies in the simulations form gradually over time in the hierarchical fashion characteristic of the CDM cosmogony. In the ΛCDM model, substantial galaxies first appear at z≃5 and the population builds up rapidly until z = 1 after which the rate of galaxy formation declines as cold gas is consumed and the cooling time of hot gas increases. In the SCDM simulation, the evolution is qualitatively similar, but is shifted towards lower redshift. In both cosmologies, the present-day K-band luminosity function of the simulated galaxies resembles the observations. The galaxy autocorrelation functions differ significantly from those of the dark matter. At the present epoch there is little bias in either model between galaxies and dark matter on large scales, but a significant anti-bias on scales of ∼ 1 h−1 Mpc and a positive bias on scales of ∼ 100 h−1 kpc is seen. The galaxy correlation function evolves little with redshift in the range z = 0–3, and depends on the luminosity of the galaxy sample. The projected pairwise velocity dispersion of the galaxies is much lower than that of the dark matter on scales less than 2 h−1 Mpc. Applying a virial mass estimator to the largest galaxy clusters recovers the cluster virial masses in an unbiased way. Although our simulations are affected by numerical limitations, they illustrate the power of this approach for studying the formation of the galaxy population.