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

Discussion
lensing distortion signal by unlensed cluster members was employed in turn
to measure the cluster light. It was applied to deep Subaru and HST /ACS
imaging of A1689, a massive galaxy cluster at a relatively low redshift (z =
0.183), which is a known strong lens. We derived radial light profile of the
cluster, a color profile and radial luminosity functions more reliably than
the usual approach of simply subtracting background counts. the data, r <
2 h −1 Mpc, with a constant slope, d log(L)/d log(r) = −1.12±0.06, unlike the
lensing mass profile which steepens continuously with radius. We derived the
radial profile of the M/L ratio, which has not been previously constrained
in such detail, due to the difficulty of measuring mass and light profiles with
such accuracy and free of systematic effects. We found that M/L peaks
at an intermediate radius, ∼ 100 h −1 kpc, with a somewhat high value of
M/L B ∼ 400h(M/L) ⊙ , and then falls at larger radius. The cluster luminosity
function was found to have a flat slope, α = −1.05 ± 0.05, independent of
radius and with no faint upturn to M i ′ < −12 as claimed in previous work.
We established that the very bluest objects are negligibly contaminated by
the cluster (V − i ′ < 0.2), because their distortion profile rises towards the
center following the red background, but offset higher by ≃ 20%, consistent
with the greater estimated depth of the faint blue galaxies, 〈z〉 ∼ 2 compared
to 〈z〉 ∼ 0.85 for the red background. Finally, we improved upon our earlier
mass profile by combining both the red and blue background populations,
clearly excluding low-concentration CDM profiles.
In Chapter 3 I further employed my methods to explore three massive
clusters where excellent multi-band data are available. We discovered that
the color-color space can be used to better separate cluster members from the
foreground and background populations behind clusters A1703 (z = 0.258),
A370 (z = 0.375) and RXJ1347-11 (z = 0.451) imaged with Subaru. The
clustering of cluster members reveals that they are confined to a distinct
region of CC space. A reliable background sample for weak lensing measurements
was obtained by selecting red background galaxies from the CC
diagram whose weak lensing signal is undiluted, and adding to those faint
blue galaxies, whose weak lensing signal is in good agreement with the red
galaxies. We avoided dilution of the weak lensing signal by identifying and
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