Simulations of galaxy formation in a cosmological volume

We present results of large N-body-hydrodynamic simulations of galaxy forma tion. 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, Omega = 1 SCDM model and the flat, Omega = 0.3 Lambda CDM model. Over 2000 galaxies form in each of these simulations. We examine the rate a t which gas cools and condenses into dark matter haloes. This roughly track s the cosmic star formation rate inferred from observations at various reds hifts. Galaxies in the simulations form gradually over time in the hierarch ical fashion characteristic of the CDM cosmogony. In the Lambda CDM model, substantial galaxies first appear at z similar or equal to 5 and the popula tion 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 sh ifted towards lower redshift. In both cosmologies, the present-day K-band l uminosity function of the simulated galaxies resembles the observations. Th e galaxy autocorrelation functions differ significantly from those of the d ark matter. At the present epoch there is little bias in either model betwe en galaxies and dark matter on large scales, but a significant anti-bias on scales of similar to1 h(-1) Mpc and a positive bias on scales of similar t o 100 h(-1) kpc is seen. The galaxy correlation function evolves little wit h redshift in the range z = 0-3, and depends on the luminosity of the galax y sample. The projected pairwise velocity dispersion of the galaxies is muc h lower than that of the dark matter on scales less than 2 h(-1) Mpc. Apply ing a virial mass estimator to the largest galaxy clusters recovers the clu ster virial masses in an unbiased way. Although our simulations are affecte d by numerical limitations, they illustrate the power of this approach for studying the formation of the galaxy population.