From: Joseph Hennawi (joeh@berkeley.edu)
Date: Wed Jan 25 2006 - 01:07:46 PST
Here is an aggressively truncated version of the strong lensing text.
I need to know if there are any lensing clusters on the cycle 15
target list.
Strong gravitational lensing by clusters is a powerful test of the
$\Lambda$CDM model, probing the rare, highest mass concentrations in
the Universe, where the dark matter density is highest. However, the
frequency of giant arcs observed in the RCS survey (Gladders \etal
2003) suggests that strong lensing by high redshift clusters is at
odds with the predictions of $\Lambda$CDM. Although numerical
simulations predict that the distribution of lensing clusters should
be peaked at $z \sim 0.4$ (Hennawi \etal 2006), {\em all} the lensing
clusters in the RCS sample are at $z\gtrsim 0.7$. In addition, the
presence of several high redshift clusters with multiple arcs at large
Einstein radii, have led many to speculate that these systems might
constitute a distinct population of `superlenses', with extremely
large lensing cross sections (Gladders et al. 2003; Dalal et al. 2004)
-- whereas $\Lambda$CDM predicts no such structures (Hennawi \etal
2006). Our cycle 14 sample already contains 2 (?) new giant arc
systems lensed by $z \gtrsim 1$ clusters, nearly doubling the number
known. These are in addition to the known high redshift lensing
cluster on our cycle 15 target list (IS THERE ONE?). The image quality
delivered by the ACS dramatically increases the number of the number
of faint, low surface brightness arcs and image families
detectable. Detailed modeling of these distorted image positions, will
enable high fidelity reconstructions of the dark matter distribution,
similar to the recent analysis of Abell 1689 by the ACS GTO team
(Broadhurst et al. 2005), but for clusters at $z \gtrsim 1$.
Cheers,
Joe
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