The physical properties of the redshift-three intergalactic medium from studies of QSO absorption line systems

Details The physical properties of the redshift-three intergalactic medium from studies of QSO absorption line systems The physical properties of the redshift-three intergalactic medium from studies of QSO absorption line systems

Jul 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt.........8k&link_type=abstract

Thesis (PhD). UNIVERSITY OF CALIFORNIA, SAN DIEGO, Source DAI-B 60/01, p. 220, Jul 1999, 157 pages.

Computer Science

Redshift 3

Scientific paper

We present high quality optical and ultraviolet spectra of several high redshift QSOs, from the W. M. Keck and Hubble Space telescopes. We use the absorption lines from these spectra to study several aspects of the z ~ 3 intergalactic medium (IGM), including: (1) the distribution of clumped and smoothly distributed baryonic material; (2) The spectral shape of the ultraviolet ionizing background (UVB); (3) The properties of hierarchical merging events at z ~ 3, and (4) the baryonic content of the Universe. We have determined the statistical distributions which describe the Lyα forest absorption in neutral hydrogen (H I), and have shown that there are vast numbers of absorbers with H I column densities N HI < 1013 CM-2. We have used observations of singly ionized helium (HeII) Lyα forest absorption to show that there are not a significant number of absorbers with NHI < 1012 CM-2. We use observations of HeII Gunn-Peterson absorption to infer that only 1 to 5% of all baryons are in a smooth component of the IGM at z ~ 3. The rest of the baryons may be in the Lyα forest, with only <10 % in collapsed objects such as protogalaxies. We show that the UVB has a soft spectrum, with η ≡ 1.77J912/ J228 > 104, indicating the Universe is not fully reionized at z ~ 3. We have placed a strong upper limit on the primordial deuterium to hydrogen ratio in a Lyman limit system (LLS) with simple velocity structure, and show that D/H is low: D/H < 6 × 10-5. This limit is consistent only with previous measurements of D/H which indicate the Universe's baryon density is Ωbh2 = 0.019. We present the only two known intervening absorption systems which show O VI. These O VI absorbers are associated with LLS which display some, but not all, of the properties expected of a z ~ 3 hierarchical merging event.

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