Astronomy and Astrophysics – Astrophysics
Scientific paper
1997-07-22
Astronomy and Astrophysics
Astrophysics
21 pages Latex with 6 embedded figures, submitted to ApJ
Scientific paper
10.1086/305211
The standard method of measuring the galaxy pairwise velocity dispersion on small scales is heavily weighted by the densest regions in a way that is difficult to calibrate. We propose a new statistic which measures the small-scale velocity dispersion as an explicit function of density. Computing this statistic for a volume-limited subsample of the Optical Redshift Survey, we find that the small-scale velocity dispersion rises from 220 to 760 km/s as density increases. We calculate this statistic for a series of mock catalogs drawn from a hydrodynamic simulation of an \Omega h = 0.5 Cold Dark Matter universe (standard CDM), and find that the observed velocity distribution lies ~1 \sigma below the simulations in each of eight density bins, formally ruling out this model at the 7.4 \sigma level, quantifying the well-known problem that this model produces too high a velocity dispersion. This comparison is insensitive to the normalization of the power spectrum, although it is quite sensitive to the density and velocity bias of galaxies relative to dark matter on small scales. (abridged)
Cen Renyue
Ostriker Jeremiah P.
Strauss Michael A.
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