Mathematics – Logic
Scientific paper
Mar 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...424...22c&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 424, no. 1, p. 22-29
Mathematics
Logic
9
Astronomical Models, Cosmology, Density Distribution, Galactic Structure, Virgo Galactic Cluster, Cosmic Background Explorer Satellite, Hubble Constant, Universe, Velocity Distribution
Scientific paper
The Local Supercluster kinematic properties (the Local Group infall toward the Virgo Cluster and galaxy density distribution about the Virgo Cluster) in various cosmological models are examined utilizing large-scale N-body (PM) simulations 5003 cells, 2503 particles, and box size of 400 h-1 Mpc) and are compared to observations. Five models are investigated: (1) the standard, Cosmic Background Explorer Satellite (COBE)-normalized cold dark matter (CDM) model with omega = 1, h = 0.5, and sigma8 = 1.05; (2) the standard Hot Dark Matter (HDM) model with omega = 1, h = 0.75, and sigma8 = 1; (3) the tilted CDM model with omega = 1, h = 0.5, n = 0.7, and sigma8 = 0.5; (4) a CDM + lambda model with omega = 0.3, lambda = 0.7, h = 2/3, and sigma8 = 2/3; (5) the PBI model with omega = 0.2, h = 0.8, x = 0.1, m = -0.5, and sigma8 = 0.9. Comparison of the five models with the presently available observational measurements vLG = 85 - 305 km/s (with mean of 250 km/s), delta(ng)/(ng-bar) = 1.40 + or - 0.35) suggests that an open universe with omega approximately 0.5 (with or without lambda) and sigma8 approximately 0.8 is preferred, with omega = 0.3-1.0 (with or without lambda) and sigma8 = 0.7-1.0 being the acceptable range. At variance with some previous claims based on either direct N-body or spherical nonlinear approaches, we find that a flat model with sigma8 approximately 0.7-1.0 seems to be reasonably consistent with observations. However, if one favors the low limit of vLG = 85 km/s, then an omega approximately 0.2-0.3 universe seems to provide a better fit, and flat (omega = 1) models are ruled out at approximately 95% confidence level. On the other hand, if the high limit of vLG = 350 km/s is closer to the truth, then it appears that omega approximately 0.7-0.8 is more consistent. This test is insensitive to the shape of the power spectrum, but rather sensitive to the normalization of the perturbation amplitude on the relevant scale (e.g., sigma8) and omega. We find that neither linear nor nonlinear relations (with spherical symmetry) are good approximations for the relation between radial peculiar velocity and density perturbation, i.e., nonspherical effects and gravitational tidal field are important. The derived omega using either of the two relations is underestimated. In some cases, this error is as large as a factor of 2-4.
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