9213(  1) - 12/20/00 23:44  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      9213
                                                       Version: 1
                                                       Check-in Date: 20-Dec-2000
                                                                      23:37:55

1.Proposal Title:
Constraints on the Metal Enrichment History from Observations of Highly Ionized Gas
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2. Proposal For  3. Cycle
AR               10
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4. Investigators
                                                                                     Contact?
    PI: Michael Rauch                     Carnegie Observatories
   CoI: Dr. Alain Smette                  Goddard Space Flight Center                   N
   CoI: Prof. Matthias Steinmetz          Steward Observatory                           N
   CoI: Dr Martin Haehnelt                Max-Planck-Institute                          N
   CoI: Dr Joop Schaye                    Institute of Astronomy                        N

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5. Abstract

Galaxies up to very high redshifts appear to be embedded in a highly ionized, metal
enriched gas of unknown origin. Based on the presence of OVI absorption in QSO
spectra this gas has sometimes been speculatively associated with a hot
collisionally ionized phase, possibly ejected by winds or stripped from galaxies
moving through an ambient medium. Recent hydrodynamical simulations of galaxy
formation suggest an alternative explanation in that OVI may also trace diffuse
photoionized gas ejected at high redshift during a `Population III' phase of star
formation. In the latter case the gas would now be at a relatively low temperature,
surrounding galaxies out to large distances, and falling into them at the epoch of
observation. Both scenarios, current ejection of hot collisionally ionized gas
(``galactic origin'') or infall of pre-enriched gas onto forming galaxies (``pre-
galactic origin'') have observational consequences pertaining to the measurable
absorption line width, column density, and cross- section. Studying absorption by
the OVI gas in several ionic transitions in the high quality STIS spectra of QSOs
already in the HST archive should be able to tell us which ionization process is
responsible for the presence of OVI, and how widely intergalactic metal enrichment
has spread, as a function of time.
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                                                9213(  1) - 12/20/00 23:44  - [  2]

            Summary Form for Proposal  9213

  Item                         Used in this proposal
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  Proposal Category            AR
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