9204(  1) - 12/20/00 23:41  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      9204
                                                       Version: 1
                                                       Check-in Date: 20-Dec-2000
                                                                      23:34:11

1.Proposal Title:
The Ages of Very Red Spheroids and Bulges and Associated Disks  at  Redshifts z ~
0.8
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2. Proposal For  3. Cycle
AR               10
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4. Investigators
                                                                                     Contact?
    PI: David Koo                         UCO/Lick Observatory, University of
                                          California, Santa Cruz
   CoI: Dr. Christopher Willmer           Lick Observatory, University of California    N
   CoI: Dr. Myungshin Im                  Lick Observatory, University of California    N
   CoI: Dr. Luc Simard                    Steward Observatory, University of Arizona    N
   CoI: Mr. Stuart Norton                 University of California, Santa Cruz          N

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5. Abstract

The ages of spheroids remain an important mystery amenable to direct attack with HST
color images. Hierarchical galaxy formation models predict that bulges are redder
than associated disks and that field spheroids should be younger (bluer) and have
larger age scatter than their older, more coeval, cluster cousins. Using Keck and
HST data, van Dokkum et al. have measured the galaxy half-light colors for 30
cluster E/S0's at z ~ 0.8 and find very red colors with small scatter. For 26 field
galaxies at z ~ 0.7 - 1, we have measured separate colors for bulges and disks and
find that the disks are indeed all bluer than the bulges. To our surprise, the field
bulges are as red or redder than the cluster galaxies. These results are major steps
forward, but unfortunately, the high-redshift field bulges are so red that the
exposures were too shallow in the bluer band (2800s in V) to yield positive measures
of color scatter for direct comparison to cluster results. Moreover, our surprise
may be explained if the color of cluster bulges are redder than their galaxy's half-
light color (which may be contaminated by bluer disks). We aim to remedy both
problems with this archive proposal and thereby answer the cosmologically important
question: What are the relative color (age) distributions of spheroids, bulges, and
disks among high redshift z ~ 0.8 galaxies in both field and cluster environments?
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                                                9204(  1) - 12/20/00 23:41  - [  2]

            Summary Form for Proposal  9204

  Item                         Used in this proposal
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  Proposal Category            AR
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