![]() ![]() © CAMBRIDGE UNIVERSITY PRESS 1999
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2.4. Fraction of Galaxies in Clusters
The fraction of galaxies in rich
R 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
0 clusters
within 1.5h-1 Mpc radius and
m
m3 + 2m is
<NR>median
50, or
<NR>mean
56. For R
1 clusters the average is
<NR>median
60, or
<NR>mean
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
(
L*) galaxies in
R
0
clusters (within RA = 1.5h-1 Mpc) is
![]() | (1) |
The average overall (field) number density of bright
(
L*) galaxies is
![]() | (2) |
The average galaxy overdensity in rich (R
0) clusters (within
1.5h-1 Mpc radius) is thus
![]() | (3) |
The typical threshold galaxy overdensity in clusters (within 1.5h-1 Mpc radius) is
![]() | (4) |
![]() | (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
![]() | (6) |