10985(  1) - 04/03/06 11:23  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10985

Version: 1    Check-in Time: 03-Apr-2006 15:23:02

Title
Mapping Out Subtructure in Galaxy Clusters using Strong Lensing
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Type             Cycle     Parallel Pointing Tolerance
AR               15        <none>
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Investigators
                                                                                     Contact?
    PI: Dr. Liliya L.R. Williams          University of Minnesota - Twin Cities

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Abstract

In the last fifteen years Hubble Space Telescope has observed many galaxy clusters
that host multiple images of background strongly lensed galaxies. The precision of
HST's astrometry and the depth of its photometry are often necessary to identify and
characterize the faint images of galaxy sources. These data have been used by many
workers to model the projected mass distribution in clusters with the goal of
deducing the properties of dark matter based on its observed clumping. However, most
of the mass reconstruction work has been done using parametric mass models. Such
models presuppose a close relationship between the distribution of the dark matter
and that of light. The upshot is that the parameter space of solutions is not fully
explored, and also, the observed image positions need not be well fit by the model.
In order to utilize the high precision of HST data, I propose to use a free-form, or
non-parametric mass modeling technique to reconstruct the detailed mass distribution
in two clusters, SDSS J1004+4112 (14 images; z=0.68), and Abell 1689 (106 images;
z=0.18), both observed with the HST in the last few years. The method fits the
observed image positions exactly, does not impose restrictive assumptions on the
mass, and explores the whole parameter space of mass models that are consistent with
the observed lensing data. The method is thus able to see variable mass-to-light
ratios of cluster galaxies, sizes of dark matter halos of galaxies, variations of
the galaxy halo properties with the distance from the cluster center, and
misalignments between mass and light centroids of clusters. In order to characterize
the uncertainties of the method I will perform reconstructions on synthetic lenses
whose mass distribution is known.
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