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2.7. Central Density and Core Size
Central number density of galaxies in rich compact clusters (Bahcall 1975, 1977; Dressler 1978) is (for galaxies in the brightest 3 magnitude range)
The central density reaches ~ 104h3 galaxies Mpc-3 for the richest compact clusters. The typical central mass density in rich compact clusters, determined from cluster dynamics is
where r,c is the radial (line-of-sight) central cluster velocity dispersion (in km s-1) and Rc is the cluster core radius (in Mpc).
Core radii of typical rich compact clusters, determined from the galaxy distribution (Bahcall 1975; Dressler 1978; Sarazin 1986) are in the range
Core radii of the X-ray emitting intracluster gas (Section 3) are
The core radius of the mass distribution determined from gravitational lensing observations of some clusters may be smaller, Rc 50 kpc, than determined by the galaxy and gas distribution.
The typical central density of the hot intracluster gas in rich clusters (Section 3) is