From: Mike Gladders (gladders@ociw.edu)
Date: Thu Jan 26 2006 - 16:37:14 PST
Yes my biggest issue with the previous text was also the stretch to
A1689. Those observations found >100 arc iamges in 30 image families -
we aren't comparable. Not that what we have isn't important, but we
WON't get the kind of reconstructions of mass profiels etdc out of these
data that were gotten from A1689.
M
On Thu, 26 Jan 2006, Joseph Hennawi
wrote:
> I agree that the weak lensing should not be compressed, but I think
> the strong lensing science is compelling because
>
> a) There is suggestive evidence for disagreement with LCDM at high
> redshift
> b) It is probing the nature of dark matter which is the kind of
> 'fundamental physics' the TAC will like
>
> Chris Mullis has found an arc in 2 z-band orbits and 1 i-band orbit
> behind an XMM cluster at z = 1.39, which makes this the highest
> redshift lensing cluster known to my knowledge, and the SN cluster
> sample has roughly doubled the number of arcs known behind z ~ 1
> clusters. These discoveries should be mentioned.
>
> I agree that the comparison to Abell 1689 is a stretch, but I was
> trying to relate the lensing science to the HST GTO work which has
> had a very high profile. That said, RCS2319+0038
> (z=0.91), which is on the cycle 14 target list has three giant arcs
> in a shallow ground based image. So a detailed reconstruction could
> be possible there. This does not make a good argument for cycle 15
> though, unless there is an analogous system on the cycle 15 target list.
>
> How about if we put the strong lensing science at the end of the WL
> section, since the two are actually complementary. Weak lensing + 1
> giant arc can measure the
> concentration of the high redshift cluster. We have done simulations
> that show this is feasible but the paper is not out yet (although we
> didn't simulate z ~ 1).
>
> So we could say something like the following
>
> (first part should be shortened).
>
> 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. Our cycle 14
> sample
> already contains 3 new giant arc systems lensed by $z \gtrsim 1$
> clusters, doubling the number
> known, including a giant arc lensed by a cluster at $z = 1.39$
> which is the highest redshift lensing cluster known. These are in
> addition to the
> known high redshift lensing cluster on our cycle 15 target list
> (mention how many).
> The image quality delivered by the ACS dramatically increases the
> number of the number
> of faint, low surface brightness arcs and image families
> detectable. A single high redshift giant arc in a cluster measures
> the mass interior to the Einstein radius (~ 100 kpc/h), and is thus
> highly complementary
> to the larger scale weak lensing measurements. By combining this small
> scale strong lensing constraint with the larger scale weak lensing
> analysis,
> which constrains the mass interior to the virial radius, we will be able
> to measure the concentration parameters of the clusters. Our
> unprecendented
> deep imaging survey of high redshift clusters will thus allow us to
> determine if there really are
> 'superlenses' at high redshift and make the first measurements of the
> profiles of dark matter
> halos at z \gtrsim 1.
>
>
>
>
>
> On Jan 26, 2006, at 2:34 PM, Henk Hoekstra wrote:
>
> > Hi Saul et al.,
> >
> > I have been looking at the proposal pdf file on the website (not sure
> > this is the right place), but I am wondering whether we should start
> > the proposal differently, highlighting the NEW things we can do with
> > the cycle 15 observations.
> >
> > The way it reads now it's more of the same (everybody wants more
> > data...)
> > and only later on it becomes clear we want to do all kinds of new
> > things.
> >
> > I noticed the weak lensing has been cut considerably, but I think
> > we should be careful not to compress it too much. For instance, my
> > feeling is that the strong lensing part is too long. So far the
> > strong lensing hasn't been overwhelming, and I am not sure it will
> > ever be... these are high-z clusters after all. I don't think the
> > sample of clusters studied here will really advance the science
> > questions
> > posed in this section by a significant amount. Also I don't believe
> > we'll do as well as what has been done for A1689. Nothing obvious
> > is seen in the current data. A somewhat longer integration time
> > won't help
> > there.
> >
> > Virial masses: also too long, as it describes other data that we want
> > to obtain. We could simply say that
> >
> > "We are acquiring X-ray and plan to obtain SZ measurements as part
> > of a
> > multiwavelength strategy of determining cluster masses through
> > lensing, X-ray and SZ in order to understand cluster physics and
> > formation."
> >
> > and copy some stuff from my lensing write up about how this helps
> > studies of cluster abundance and cosmology.
> >
> > In short I think we can condense the strong lensing section and virial
> > mass section in a short paragraph and tie it in with the weak lensing
> > as a "Determination of cluster masses" section.
> >
> > Cheers,
> > Henk
> >
> >
> > On Thu, Jan 26, 2006 at 01:10:09PM -0800, Saul Perlmutter wrote:
> >> Our Cycle 14 program has now proven a new extremely efficient
> >> approach
> >> to obtain z>1 dust-free Type Ia supernovae, and we here propose to
> >> capitalize on this new technique . We will collect a total sample of
> >> ~20 z>1 SNe Ia in cluster ellipticals, yielding dark energy
> >> measurements
> >> that do not suffer from the major systematic uncertainty at these
> >> redshifts, that of the extinction correction with a prior. By
> >> targeting
> >> massive galaxy clusters at z>1, we obtain a five-times [CHECK]
> >> higher
> >> efficiency in detection of Type Ia supernovae in elliptical galaxies,
> >> and provide a well-understood host galaxy environment. These same
> >> deep
> >> cluster images then also yield fundamental calibrations required for
> >> future weak lensing and Sunyaev-Zel'dovich measurements of dark
> >> energy,
> >> as well as an entire program of cluster studies. The data will make
> >> possible a factor of two improvement on supernova constraints on dark
> >> energy time variation, and much larger improvement in systematic
> >> uncertainty, taking advantage of the uniquely well-controlled host
> >> environment that clusters provide. They will provide both a cluster
> >> dataset and a SN Ia data set that will be a longstanding scientific
> >> resource.
>
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