LBL Cosmology Visitor Program
Weak Lensing workshop
Day 2 discussions
* Monday, Aug. 9, morning discussions will focus on using
weak lensing for cluster finding, and for mapping cluster
profiles. The afternoon will either continue this or
concentrate on space/ground issues.
* The community benchmark tests of shear extraction by
various groups on the same catalogs - STEPS? - could take a
first step at the LBL workshop with the participants next
week serving to prototype the comparison. Will space data
be available?
* More discussion of the importance of source redshift
distribution, and the relative slowness of the z^2 e^{-z^1.2}
drop off. The z>3 sources make a significant contribution
in this case. What are the effects for space/ground?
This led to a discussion of whether z_median was actually an
appropriate measure to use in comparing surveys. Henk pointed
out that even just z_mean would be superior. Generally the
results could be very sensitive to z so we need better
estimators of the source redshift distribution.
As a practical concern in simulations, where should the data
outputs start? One might likely need to begin dumps at z=5.
* sigma8 seems to agree within 1-2sigma from the different
WL experiments, but this is still far from the 1% precision desired.
* Rule of thumb of the day [Henk]: "If you can measure photo-z's,
you can measure shapes".
* Again, how to use multiband information? At the least, multiple
bands give effectively increased exposure time, and one would
presumably weight the shapes from each filter by S/N. But what
added value do multiple filters bring for shape determination?
Are there pros/cons for systematics?
* Observations - when will it be practical to have sufficiently
good observations to achieve 1) tomography, 2) CCC/offset-linear
method. Henk says VLT gets an effective number density of
galaxies of 15/min^2. Once you divide this into bins, you get
killed as n^2, which you have to make up with a very large area,
but systematics will limit this at some point.
* Some discussion of photo-z's and training sets vs. templates.