10306(  1) - 04/02/04 11:32  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      10306
                                                       Version: 1
                                                       Check-in Date: 02-Apr-2004
                                                                      11:32:02

1.Proposal Title:
Archival Study of Merger-Induced Populations in Early-Type Galaxy Cores
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2. Proposal For  3. Cycle  4. Parallel Pointing Tolerance
AR               13        <none>
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5. Investigators
                                                                                     Contact?
    PI: Ms. Jodie R. Martin               The University of Virginia
   CoI: Dr. John Hibbard                  Associated Universities, Inc.                 N
   CoI: Prof. Robert W. O'Connell         The University of Virginia                    N
   CoI: Dr. Swara Ravindranath            Space Telescope Science Institute             N
   CoI: Dr. Roeland van der Marel         Space Telescope Science Institute             N

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6. Abstract

Hierarchical formation models predict that early-type galaxies are built up over an
extended period from mergers of smaller systems, a process which should leave long-
lived signatures in their light profiles and stellar population colors. Merger
events should have continued up to relatively recent times (the last 1-5 Gyr), and
many ellipticals and S0 bulges should therefore show evidence of multiple, discrete,
intermediate-age populations. Although there is substantial observational support
for a dissipational merger origin for some early-type galaxies, most do not exhibit
the expected anomalies in either their light profiles or color distributions.
However, existing searches have primarily been monochromatic and those which used
multi-bands studied only narrowly defined subsamples of early-type galaxies. Here we
propose an archival study of high resolution, broad-band, multi-color images of the
cores of a large sample of 167 early-type galaxies which are representative of the
general population. This is the most extensive search intended to probe spatially-
segregated, multiple population components with ages in the range 1-5 Gyr. Our
sample consists of early-type galaxies in a wide range of environments from the
field to groups to rich clusters. There is very little information on the color
structure of core stellar populations of early-type galaxies in different
environments and how they may relate to gaseous merger histories and our program
would effectively explore new terrain. Simulations of mergers show that gas
generally falls deep into the potential well to scales within a few 100 pc of the
center before forming stars. An effective search for distinct populations must
therefore be able to resolve these scales, which is possible for a meaningfully
large sample only with HST.
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            Summary Form for Proposal  10306

  Item                         Used in this proposal
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  Proposal Category            AR
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