Wednesday, May 10, 2006

Shapelet Catalogs & Clusters

SDSS Shapelets

I've been working on shapelet decompositions for
all spectroscopic galaxies from SDSS DR4, in all
5 SDSS banspasses. The primary motivator is
realistic simulations for the Dark Energy Survey,
but there can be a lot of science in this catalog as well.
Basically you transform the image into a two
dimensional basis, sort of like a fourier transform.
From that you can define a reconstruction. We
are using the reconstructions to make realistic
simulated galaxies for the sim. There is even
a technique to perturb the reconstruction in a
way that doesn't just produce random junk. This
way the hundreds of millions of galaxies simulated won't be
just be copies of the hundred thousand I decomposed.

I will write this up after I'm done, even if it is just to
post on astro-ph. They are all running now and will
be finished in a few days.


I've been looking a lot at the maxbcg cluster catalog.
It is an excellent catalog and is very well tested at the
high mass end. I've been identifying issues that
don't really affect the high mass end but do affect the
low mass end. This is important to me because there
is a lot of lensing signal in these low mass objects and
if we can construct a believable catalog there it will
be great for lensing and will in general allow a more
complete examination of structures larger than
individual galaxies. With SDSS we can really do this.
Berlind has done this with the spectroscopic sample at
low redshift and this is our chance to do a uniformly
selected sample to higher redshift. Because of the
extra volume this will also just have a lot more statistical
power in certain ways.

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