Mass and Light distributions in Clusters of Galaxies - Henry A ...

4.3 Sample selection from the color-color diagram
x 10 −6
7
3
6
2.5
5
B − R
2
1.5
4
3
Number/pix 2
1
2
0.5
1
0
0 0.5 1 1.5
R − Z
0
3.5
3.5
3
E−type
3
2.5
2.5
B − R
2
1.5
2
1.5
redshift
1
S0
0.5
Sa
Sd
0
−0.5 0 0.5 1 1.5 2
R − Z
1
0.5
0
Figure 4.1 – Top: Number density in B J − R C vs. R C − z ′ CC space. The four distinct
density peaks are shown to be different galaxy populations - the reddest peak in the upper
right corner of the plots (dashed white line) depicts the overdensity of cluster galaxies,
whose colors lay on the red sequence; the middle peak lying blueward of the cluster
comprises mainly foreground galaxies (solid white line); the two peaks in the bottom part
(bluest in B J −R C ) can be demonstrated to comprise of blue and red background galaxies.
Together, the red+blue galaxies will serve as our “reference” background sample for WL
purposes. Bottom: B J − R C vs. R C − z ′ CC diagram, showing the distribution of galaxies
in A370. Marked are the selected foreground sample (gray) and background samples:
orange (orange), green (green), red (red), blue (blue) and dropout (magenta) background
galaxies, selected to include galaxies lying away from the cluster and foreground regions.
Overlaid are synthetic color tracks including evolution, calculated with the Galev code for
an elliptical, S0, Sa and Sd type models.