9541(  1) - 12/06/01 12:46  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      9541
                                                       Version: 1
                                                       Check-in Date: 06-Dec-2001
                                                                      11:49:37

1.Proposal Title:
Formation of Elliptical and S0 Galaxies in Clusters
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2. Proposal For  3. Cycle
AR               11
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4. Investigators
                                                                                     Contact?
    PI: Pieter van Dokkum                 California Institute of Technology

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5. Abstract

Establishing the formation mechanism of cluster galaxies gives direct information on
the origins of the Hubble sequence and the morphology-density relation. Extensive
studies with HST have led to a basic understanding of the star formation histories
of cluster galaxies, but assessing the time and mechanism of their structural
assembly has proven difficult, and has led to conflicting results. The main problem
is the difficulty in distinguishing elliptical and S0 galaxies at high redshift.
This proposal asks support to re-analyze the exquisite archival WFPC2 data on
clusters at z~ 0.5 using two novel techniques, with the aim of determining
objectively when and how elliptical and S0 galaxies in clusters were assembled. The
goals are 1) to unambiguously distinguish elliptical and S0 galaxies in distant
clusters using their ellipticities combined with spatially resolved kinematics, and
2) to determine the evolution of the galaxy merger fraction in clusters from the
incidence of close pairs. Together, these projects give important new constraints on
the assembly time of massive galaxies, and will put the ``elliptical versus S0''
controversy to rest. Keck spectroscopic data allowing measurements of spatially
resolved kinematics are already obtained for 39 galaxies in four clusters. As a
``bonus'', the cluster-to-cluster scatter in the intermediate redshift Fundamental
Plane of early-type galaxies will be determined.
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                                                9541(  1) - 12/06/01 12:46  - [  2]

            Summary Form for Proposal  9541

  Item                         Used in this proposal
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  Proposal Category            AR
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