9520(  1) - 12/06/01 12:33  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      9520
                                                       Version: 1
                                                       Check-in Date: 06-Dec-2001
                                                                      11:44:07

1.Proposal Title:
Theoretical Modeling of the Metagalactic Ionizing Radiation Background and IGM
Metallicities
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2. Proposal For  3. Cycle
AR               11
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4. Investigators
                                                                                     Contact?
    PI: Michael Shull                     University of Colorado, Boulder
   CoI: Prof. Mark Giroux                 East Tennessee State University               N
   CoI: Mr. Matthew Browning              University of Colorado, Boulder               N
   CoI: Mr. Jason Tumlinson               University of Colorado, Boulder               N

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5. Abstract

We propose a theoretical exploration of the metagalactic ionizing background
radiation, applied to understanding the baryon content, metallicity, and
nucleosynthetic history of the intergalactic medium (IGM). Photoionization by
quasars and starburst galaxies appear to dominate the ionization of hydrogen,
helium, and many heavy elements (C, Si, N, O) observed by Hubble and FUSE through
quasar absorption-line systems. In order to make precision measurements of the total
gas mass and metallicity, one must apply substantial ``ionization corrections" to
the observed ion stages (e.g., H I, He II, Si III, Si IV, C III, C IV). New high-
quality data from STIS and COS will require us to develop ionization models at
higher level of precision from the present (Haardt & Madau 1996; Fardal, Giroux, &
Shull 1998). These new models will include accurate atomic data, ionizing source
spectra, IGM opacity, and cosmological radiative transfer calculations, with many
underlying theoretical issues. We propose to develop a web-based tool designed to
calculate the metagalactic ionizing background and ionization corrections at epochs
from z ~ 6 down to the present. Our models will be available to the astronomical
community on a CU-maintained website, which could be linked to the STScI. These
precision calculations are a critical tool for the key absorption-line science done
with spectrographs aboard HST (STIS, COS) and FUSE.
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                                                9520(  1) - 12/06/01 12:33  - [  2]

            Summary Form for Proposal  9520

  Item                         Used in this proposal
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  Proposal Category            AR
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