10321(  1) - 04/02/04 11:56  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      10321
                                                       Version: 1
                                                       Check-in Date: 02-Apr-2004
                                                                      11:55:42

1.Proposal Title:
Determining the formation epoch of dwarf galaxies using the HST/ACS Ultra Deep Field
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2. Proposal For  3. Cycle  4. Parallel Pointing Tolerance
AR               13        <none>
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5. Investigators
                                                                                     Contact?
    PI: Dr. Armando Gil de Paz            Carnegie Institution of Washington
   CoI: Dr. Kai G. Noeske                 University of California - Santa Cruz         N
   CoI: Dr. Barry F. Madore               Carnegie Institution of Washington            N
   CoI: Dr. David C. Koo                  University of California - Santa Cruz         N

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6. Abstract

We will analyze the outer parts of the surface brightness and color profiles of
dwarf star-forming galaxies at redshifts between 0<z<1 in the four bands of the
HST/ACS Ultra Deep Field (UDF). Only in these outer regions of the profiles,
emission from the centrally concentrated star-forming activity becomes negligible,
allowing one to derive properties of the evolved stellar low-surface-brightness
halo. The comparison of the colors of the galaxy halos with the predictions of
evolutionary synthesis models will allow us to estimate the epoch of formation of
these objects. In particular, we will be able to determine if dwarf galaxies formed
before the reionization epoch (z>6) or if this formation was delayed up to z~1-2 by
the intense UV-radiation field present at higher redshifts. The depth and high
spatial resolution of the UDF are required in order to detect the low-surface-
brightness stellar population associated with the galaxy halo and to separate and
spatially resolve it from the central, high-surface-brightness component.
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                                                10321(  1) - 04/02/04 11:56  - [  2]

            Summary Form for Proposal  10321

  Item                         Used in this proposal
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  Proposal Category            AR
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