8766(  1) - 12/30/99 13:06  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      8766
                                                       Version: 1
                                                       Check-in Date: 30-Dec-1999
                                                                      12:33:10

1.Proposal Title:
Color Gradients in Elliptical Galaxies at z = 0.5:  , An Indicator of Galaxy
Formation Processes
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2. Proposal For  3. Cycle
AR               9
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4. Investigators
                                                                                     Contact?
    PI: Michael Pahre                     Smithsonian Astrophysical Observatory

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5. Abstract

We propose to make a direct comparison of the frequency and size of color gradients
in cluster elliptical galaxies at z ~ 0 and z ~ 0.5 to constrain the relative roles
of merging and monolithic collapse on the galaxy formation process. Color gradients
are ubiquitous in elliptical galaxies in the local universe, and are the origin of
20-50\ Local studies of color (and line-strength) gradients could be explained by
metallicity and/or age gradients in the underlying stellar populations, but offer
few clues as to how they could have formed. HST observations at z ~ 0.5, however,
can provide direct insight into the origin(s) of these population gradients: the
gradients steepen with redshift if dissipationless merging dominates; flatten if
dissipative, gas-rich merging dominates; or remain roughly constant if monolithic
collapse (at early epochs) created the population gradients. In order to test these
predictions, we will utilize both ground-based and HST data: ground-based
observations in (U-V) at z~ 0 are a nearly exact match in color and physical
resolution to HST archival observations in (555-814) of three clusters at z ~ 0.5.
Color gradients are shown to be easily measured with HST at z ~ 0.5, but they have
yet to be studied in a systematic manner. Funding is requested here primarily to
support a Harvard undergraduate to reduce, analyze, and publish the results of the
study.
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                                                8766(  1) - 12/30/99 13:06  - [  2]

            Summary Form for Proposal  8766

  Item                         Used in this proposal
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  Proposal Category            AR
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