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

Mass and Light of A1703, A370 & RXJ1347-11
with other observables in a more statistically robust way.
Our previous work demonstrated the importance of carefully selecting
a background population to avoid contamination by the lensing cluster. It
is not sufficient to simply exclude a narrow band containing the obvious
E/S0 sequence, following common practice, because the lensing signal of the
remainder bluer objects is found to fall rapidly towards the cluster center
relative to the background of red lensed galaxies indicating that unlensed
cluster members are present blueward of the sequence diluting the true lensing
signal (Broadhurst et al. 2005b). Due to this effect, many WL studies
have underestimated the masses and concentrations of cluster mass profiles
(Lu et al. 2009), a point now widely acknowledged (Limousin et al. 2007;
Oguri et al. 2009; Okabe et al. 2009). This effect resolved the long standing
discrepancy between the strong and WL effects, with the WL signal
underpredicting the observed Einstein radius by a factor of ∼ 2.5 (Clowe
& Schneider 2001; Bardeau et al. 2005), based only on a minimal rejection
of obvious cluster members using one or two-band photometry. Red background
galaxies behind clusters have since been explored carefully with deep
wide-field spectroscopy by Rines & Geller (2008), who emphasize that the red
population in their cluster data comprises exclusively background objects.
This lensing “dilution” effect may be turned to our advantage as a means
of correcting the cluster population for background contamination, extending
the work of Medezinski et al. (2007). Here we analyze very high quality Subaru
images of A1703, A370, & RXJ1347-11 for which we have accurate WL
measurements. For these clusters, a wider range of colors is available than
for A1689, which we make full use here to improve the separation of cluster
members from foreground and background populations using the color-color
(CC) diagram and application of our dilution method. Using the dilution
method has the advantage that it does not require the actual subtraction
of background galaxies which introduces the inherent uncertainty caused by
the clustering of the background signal and the attendant requirement for
the accurate photometry of control fields.
In § 3.2 we present the cluster observations, the data reduction, and in
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