Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...436..528b&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 436, no. 2, p. 528-541
Astronomy and Astrophysics
Astrophysics
6
Astronomical Models, Cosmology, Dark Matter, Galactic Halos, Many Body Problem, Universe, Velocity Distribution, Computerized Simulation, Mathematical Models
Scientific paper
Using a large N-body simulation of a standard cold dark matter (CDM) universe in which individual dark matter galaxy halos can be resolved, the peculiar velocity field of the halos and mass particles is investigated. The rms velocity (vrms), velocity correlation function (Xivv), and the three-dimensional pairwise velocity dispersion (sigmavv) of the halos and mass are determined. The effect of halo mass and local environmnet on these function are investigated. High-mass halos with overdensities of approximately 250 and approximately 70 are good tracers of the major mass motions in the simulation as defined by a volume-averaged velocity field. Low-mass halos are biased tracers of the same field. Assuming one luminous galaxy would reside in each of the halos and the mass-to-light ratio is constant, this implies bright galaxies are fair tracers of the major mass motions in the CDM universe. The rms velocity of the halos is strongly affected by the local environmnet; the higher the background mass density the larger vrms. However, it is not straightfoward to determine the magnitude of an enhancement/suppression in the local mass density given the local enhancement/suppresion of vrms. At the end of the simulation, we obtain values of the velocity bias, bv = sigmavv, h/sigmavv, m, as a function of halo mass and minimum overdensity similar to those found by Carlberg, Crouchman, & Thomas and by Carlberg. For halos with overdensities of approximately 250 and approximately 70, bv is a decreasing function of background mass density (i.e., the higher the background density, the larger the discrepancy between the velocity dispersions of the halos and mass particles), and for halos with overdensities of approximately 2000 it is an increasing function of background density. The velocity bias as a function of scale, bv(r), is an increasing function of separation and even on larger scales, r approximately 1400 km/s, a noticeable velocity bias is present at the end of the simulation.
Brainerd Tereasa G.
Villumsen Jens V.
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