10974(  1) - 04/03/06 11:17  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10974

Version: 1    Check-in Time: 03-Apr-2006 15:17:43

Title
The Unresolved Stellar Populations of Galaxies in the HUDF: Constraints on
Hierarchical Formation
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Type             Cycle     Parallel Pointing Tolerance
AR               15        <none>
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Investigators
                                                                                     Contact?
    PI: Mr. Russell E. Ryan Jr.           Arizona State University
   CoI: Dr. Rolf A. Jansen                Arizona State University                      N
   CoI: Dr. Rogier A. Windhorst           Arizona State University                      Y
   CoI: Dr. Seth H. Cohen                 Arizona State University                      N

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Abstract

We propose a systematic Archival study of the stellar populations of >200, well-
resolved galaxies with spectroscopic redshifts in the Hubble Ultra-Deep Field
(HUDF). By fitting stellar population synthesis models to the six-filter (BVi'z'JH)
HST observations on a pixel-to-pixel basis, we can measure their stellar masses,
star formation rates, ages, and internal extinction on sub-kiloparsec scales within
each of the galaxies. This proposal has TWO major science goals: (1) Measure the
stellar population parameters on a pixel-to-pixel basis within well-resolved
galaxies at z<2. For reliable the SED fitting, we will concentrate on the ~200
galaxies with i'(AB)<26 mag and spectroscopic redshifts from the Very Large
Telescope. For an extended sample of ~50 bright galaxies without spectroscopic
redshifts, we will allow the redshift to be a fifth free parameter and generate an
additional map of best-fit photometric redshifts. This project will significantly
improve upon previous work by extending it to higher redshift for a much larger
sample and wider wavelength coverage --- ensuring more reliable statistics; (2) Use
the stellar population maps resulting from (1) to understand observed color
gradients and strongly constrain galaxy assembly as a function of Hubble type and
redshift. Given the broad spectral coverage provided by ACS and NICMOS, we will
break the infamous age-extinction-metallicity degeneracy which has plagued more
common single or two color observations. Only the HUDF data provide the sufficiently
high resolution and S/N per pixel at the critical wavelengths necessary to robustly
measure the stellar SEDs on sub-kpc scales and constrain galaxy formation scenarios.
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