11268(  1) - 03/30/07 11:18  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11268

Version: 1    Check-in Time: 30-Mar-2007 15:18:32       STScI Edit Number: 0

Title
New Synthesis Models of the Extragalactic Ionizing Background
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Type             Cycle     Parallel Pointing Tolerance
AR               16        <none>
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Investigators
                                                                                     Contact?
    PI: Dr. Piero Madau                   University of California - Santa Cruz
   CoI: Dr. Francesco Haardt              Universita' degli Studi dell' Insubria        N

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Abstract

The intergalactic medium (IGM) contains evidence of the epochs of galaxy formation,
metal enrichment, reionization, and reheating of the baryons left over from the Big
Bang. Hydrogen, helium, and many heavy elements (C, Si, N, 0) observed by Hubble
through quasar absorption line studies are kept highly ionized by the extragalactic
UV/soft X-ray background (UVB) from active nuclei and star-forming galaxies. The
spectrum and intensity of the UVB is one of the most uncertain yet critically
important astrophysical input parameters into cosmological simulations of the IGM.
It provides the ionization corrections needed for interpreting QSO absorption-line
data and derive crucial information on the distribution of primordial baryons and of
the nucleosynthetic products of star formation. We propose here to build improved
synthesis models of the UVB intensity, spectrum, and evolution with redshift using
the radiative transfer code CUBA, updating and extending our previous results
(Haardt & Madau 1996). We will adopt up-to-date determinations of the quasar
optical/X-ray luminosity functions and intrinsic spectra, intergalactic
photoelectric absorption, and cosmic star formation history from GOODS/ACS data.
This research will make use, enhance the value of and have a lasting benefit for
past and observational programs with the HST. We will make the latest version of
CUBA freely available for public use, allowing for several user-supplied quantities
such as source emissivity as a function of frequency and redshift, and amount of
intervening absorption.
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