8746(  1) - 12/30/99 13:02  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      8746
                                                       Version: 1
                                                       Check-in Date: 30-Dec-1999
                                                                      12:31:33

1.Proposal Title:
Constraints on the Flattening of Dark Matter Halos from Galaxy--Galaxy Lensing
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2. Proposal For  3. Cycle
AR               9
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4. Investigators
                                                                                     Contact?
    PI: Tereasa Brainerd                  Boston University

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5. Abstract

Deep archival imaging data will be used to investigate the degree to which the dark
matter halos of field galaxies deviate from pure spherical symmetry. The technique
that will be used is a measurement of the mean gravitational lensing shear induced
by foreground galaxies in the images of background galaxies, a phenomenon known as
galaxy--galaxy lensing. To date, all investigations of galaxy--galaxy lensing have
focused on a detection of the signal in via a circular average about the lens center
and have implicitly assumed that galaxy halos are spherically symmetric. However,
there is mounting observational evidence that dark matter halos may be substantially
flattened, in which case their projected surface mass densities will deviate from
circular symmetry. As a result, the gravitational lensing shear pattern that will be
induced by these galaxies will not be circularly symmetric about the lens center. In
this investigation the shear induced by galaxy--galaxy lensing will be computed
along direction vectors defined by the major and minor axes of the images of the
lenses, and the degree to which the shear pattern deviates from circular symmetry
will be quantified. This will be used in conjunction with Monte Carlo simulations of
galaxy--galaxy lensing by flattened halos in order to place constraints on the
overall flattening of the dark matter halos of field galaxies.
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                                                8746(  1) - 12/30/99 13:02  - [  2]

            Summary Form for Proposal  8746

  Item                         Used in this proposal
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  Proposal Category            AR
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