9937(  1) - 04/04/03 10:25  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      9937
                                                       Version: 1
                                                       Check-in Date: 04-Apr-2003
                                                                      10:24:15

1.Proposal Title:
The Ages of Distant Field Galaxy Spheroids
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2. Proposal For  3. Cycle
AR               11
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4. Investigators
                                                                                     Contact?
    PI: David Koo                         University of California - Santa Cruz
   CoI: Dr. Ricardo Schiavon              University of California - Santa Cruz         N
   CoI: Dr. Christopher Willmer           University of California - Santa Cruz         N
   CoI: Dr. Sandra Faber                  University of California - Santa Cruz         N

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5. Abstract

The ages and age spread of spheroids remain important problems in galaxy evolution
research. Both have been estimated for local galaxies via the color-magnitude
relation (CMR). To measure the CMR for distant galaxies, HST images are vital
because of the high spatial resolution needed to separate the tiny (few 0.1") bulges
from disks and because of the high precision photometry needed to measure the
dispersion in color of the spheroid subcomponent at the few % level. We have just
completed a study of field spheroids near redshift z~0.8 from the Groth Strip, using
V & I HST images and Keck redshifts. We find two surprising results: despite
evidence for ~1 mag or more of luminosity brightening, 1) the luminous spheroids
show little change from present-day U-B colors and 2) their color dispersion is
small. Due to uncertainties in the K-corrections, our results are valid only near
z~0.8. We propose here to undertake a vastly improved study with the ACS data in the
GOODS fields. The 4 filters will allow us to extend our analysis to lower and higher
redshifts. The deeper ACS data will allow us a) to improve the photometry of galaxy
subcomponents and estimates of the color dispersion, b) to measure lower luminosity
spheroids, and c) to relax our assumptions on light profile shapes. Finally, the
larger field of GOODS will enlarge the spheroid sample, thereby allowing searches
for differences in age and age spread among subsamples divided by redshift, disk
properties, bulge sizes, bulge ellipticities, etc. It should be noted that
photometric redshifts are not adequate because of correlations between colors and
derived redshifts. Thus the color dispersion work requires independent, precision
redshifts that come from spectroscopy. These will be gathered from public redshift
surveys in the GOODS fields.
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                                                9937(  1) - 04/04/03 10:25  - [  2]

            Summary Form for Proposal  9937

  Item                         Used in this proposal
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  Proposal Category            AR
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