Next Contents Previous

2.4. Fraction of Galaxies in Clusters

The fraction of galaxies in rich R gtapprox 0 clusters is ~ 5% (within the Abell radius RA = 1.5h-1 Mpc). The fraction of all galaxies that belong in clusters increases with increasing radius RA and with decreasing cluster richness threshold.

The average number of galaxies per cluster for R geq 0 clusters within 1.5h-1 Mpc radius and m leq m3 + 2m is <NR>median appeq 50, or <NR>mean appeq 56. For R geq 1 clusters the average is <NR>median appeq 60, or <NR>mean appeq 75. The number of galaxies increases to fainter luminosities following the Schechter (1976) luminosity function.

2.5. Galaxy Overdensity in Rich Clusters

The average number density of bright (gtapprox L*) galaxies in R gtapprox 0 clusters (within RA = 1.5h-1 Mpc) is

Equation 1 (1)

The average overall (field) number density of bright (gtapprox L*) galaxies is

Equation 2 (2)

The average galaxy overdensity in rich (R geq 0) clusters (within 1.5h-1 Mpc radius) is thus

Equation 3 (3)

The typical threshold galaxy overdensity in clusters (within 1.5h-1 Mpc radius) is

Equation 4 (4)
Equation 5 (5)

The galaxy overdensity increases at smaller radii from the cluster center. The galaxy overdensity in the cores of typical compact rich clusters is approximately

Equation 6 (6)

Next Contents Previous