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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)

Equation 17 (17)

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

Equation 18 (18)

where sigmar,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

Equation 19 (19)

Core radii of the X-ray emitting intracluster gas (Section 3) are

Equation 20 (20)

The core radius of the mass distribution determined from gravitational lensing observations of some clusters may be smaller, Rc ltapprox 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

Equation 21 (21)

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