Physics
Scientific paper
Sep 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt.........1f&link_type=abstract
Thesis (PHD). UNIVERSITY OF COLORADO AT BOULDER , Source DAI-B 59/03, p. 1155, Sep 1998, 206 pages.
Physics
Quasars
Scientific paper
I use existing H I and He II absorption measurements in the spectra of quasars to constrain the state of the intergalactic medium (IGM) and the ionizing background at z=2[-]4. Using quasar surveys and absorption-line spectra, I derive a new opacity model for the IGM and compute the radiation transfer through the high-redshift universe to calculate the ionizing spectrum. Most of the baryons in the universe likely reside in the IGM. I show that fluctuations in the ionizing background are substantial at that epoch and should show up in the He II absorption-line forest in particular. Observation of this effect could provide clues about the emission mechanism of quasars. Comparison of the H I and He II line opacity suggests a soft emitted spectrum and velocity broadening of the Lyα linewidths. Future ultraviolet spectroscopic missions (FUSE and HST/COS) should provide more definitive information on the IGM structure. Finally, I simulate the reionization of the universe, using a physical model for the inhomogeneities in the IGM that slow down the process. Because the observed quasars are insufficient to reionize the IGM by z/approx4.7, it appears that some yet unobserved population of hot stars or active galaxies must have provided the ionization.
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