10658(  1) - 04/05/05 12:22  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      10658
                                                       Version: 1
                                                       Check-in Date: 05-Apr-2005
                                                                      16:22:08

1.Proposal Title:
Measuring Gravitational Flexion in ACS Clusters
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2. Proposal For  3. Cycle  4. Parallel Pointing Tolerance
AR               14        <none>
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5. Investigators
                                                                                     Contact?
    PI: Dr. David Goldberg                Drexel University
   CoI: Dr. David Bacon                   University of Edinburgh, Institute for        N
                                          Astronomy

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6. Abstract

We propose measurement of the gravitational "Flexion" signal in ACS cluster images.
The flexion, or "arciness" of a lensed background galaxy arises from variations in
the lensing field. As a result, it is extremely sensitive to small scale
perturbations in the field, and thus, to substructure in clusters. Moreover, because
flexion represents gravitationally induced asymmetries in the lensed image, it is
completely separable from traditional measurements of shear, which focus on the
induced ellipticity of the image, and thus, the two signals may be extracted
simultaneously. Since typical galaxies are roughly symmetric upon 180 degree
rotation, even a small induced flexion can potentially produce a noticeable effect
(Goldberg & Bacon, 2005). We propose the measurement of substructure within
approximately 4 clusters with high-quality ACS data, and will further apply a test
of a new tomographic technique whereby comparisons of lensed arcs at different
redshifts may be used to estimate the background cosmology, and thus place
constraints on the equation of state of dark energy.
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                                                10658(  1) - 04/05/05 12:22  - [  2]

            Summary Form for Proposal  10658

  Item                         Used in this proposal
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  Proposal Category            AR
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