LargeScale Structure in a LowBias Universe
Abstract
We show that a highly evolved, or low bias, {OMEGA} = 1 cold dark matter model is compatible with current observational data. Nonlinear evolution is sufficient to account for recent observations of structure on scales ~2040 h^1^ Mpc. Within dissipationless simulations we adopt a physically plausible algorithm to select galaxies which follows their merging. Galaxy tracers are selected at redshifts ~3 and then assembled into galaxies at the current epoch. The resulting distribution is an acceptable fit to the data at a linear bias, b_l_, as low as 0.8 in a CDM model: the current microwave background limit. A simple technique is used to derive statistically correct infinite volume largescale correlations from the finite simulation cubes for both galaxies and the density; ξ_gg_ and ξ_pp_. For low bias values, b_l_~ 1, nonlinear evolution on large scales causes a modest increase in the zero crossing scale of ξ_pp_ and a substantial increase in the amplitude where it falls steeply through zero. On large scales ξ_gg_ is enhanced beyond ξ_pp_ reflecting a significant contribution from galaxies dynamically clustering into groups. On small scales ξ_pp_ steepens with evolution and, for b_l_ <~ 1.5, is not well approximated by a single power law. For b_l_ = 0.8 the galaxy correlation is a power law on small scales, ξ_gg_ is proportional to r^1.7^, and is strongly antibiased relative to the dark matter by a factor of ~2.5  3 in relative correlation amplitude at 1 h^1^ Mpc. This antibias is a consequence of increased merging in cluster halos. Within clusters, galaxies are a cooler and hence more centrally condensed population relative to the dark matter. The velocity dispersion of rich cluster galaxies is ~70% that of the dark matter. Virial analysis of a large cluster underestimates the cluster mass by a factor ~4, and gives a local estimate of {OMEGA}~ 0.27. The onedimensional pairwise dispersion of all galaxies found in the model is ~490 km s^1^ at 0.5 h^1^ Mpc. A large pairwise velocity bias exists between galaxies and density, b_v_~ 0.37. Roughly half of the velocity bias is due to the cooler galaxy population within individual cluster halos. The remainder arises because relatively fewer galaxies occur within massive high dispersion regions. Straightforward application of the cosmic virial theorem implies a {OMEGA} ~0.2.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 1992
 DOI:
 10.1086/171222
 Bibcode:
 1992ApJ...389..453C
 Keywords:

 Cosmology;
 Dark Matter;
 Galactic Clusters;
 Galactic Evolution;
 Red Shift;
 Virial Theorem;
 Astronomical Models;
 Computerized Simulation;
 Infrared Astronomy Satellite;
 Universe;
 Astrophysics;
 COSMOLOGY: DARK MATTER;
 COSMOLOGY: THEORY;
 GALAXIES: CLUSTERING;
 COSMOLOGY: LARGESCALE STRUCTURE OF UNIVERSE