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

Weak Lensing Dilution in A1689
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Distortion g +
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Distortion g +
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2 5 10 20
θ [arcmin]
2 5 10 20
θ [arcmin]
Figure 2.3 – Tangential shear profiles,
g T (r) of the red and blue background populations.
The tangential distortion profile
of both decline smoothly from the center,
remaining positive to the limit of the data.
The red galaxies are fitted well with a simple
power-law, d log g T /d log r = −1.17 ±
0.1. The blue sample is more noisy but
also well represented by the same relation,
only offset in amplitude by 23 ± 17% and
is related to the greater depth of the blue
population relative to the red, § 2.5
Figure 2.4 – Tangential shear vs. radius.
The green points represent the intermediate
color sample, containing both cluster
and background galaxies. The black points
show the level of tangential distortion of
the combined red+blue sample of the background.
The green points fall close to
the background level defined at large radii,
indicating the green sample is dominated
by background galaxies, and falls short towards
the cluster center where cluster members
increasingly dilute the lensing signal.
investigated this using the catalog of Capak et al. (2004) as here photometric
redshifts are estimated (see § 2.5 for a fuller description of the photometric
properties of this sample). First, we generated from the Capak catalog
blue/red background galaxy samples with the same color-magnitude criteria
as the present study. We then derived an i’-magnitude vs. photo-z relation
for each galaxy sub-sample. We subdivided the data into magnitude (i’) bins
and derived a magnitude (i’) vs. photo-z relation using median averaging.
We then assume this magnitude-redshift relation holds in our A1689 data
and obtain for each galaxy in A1689 an estimate of redshift via the magnitude
– photo-z relation. It is then straightforward to have an effective redshift
distribution taking into account weak lensing statistical weights, w. We can
see a qualitative feature that although low-z background galaxies are more
strongly weighted than higher-z ones, the effect on our observed redshift distribution
is negligible because our redshift selection window does not sample
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