The Nature and Distribution of Baryons in the Early Universe as Probed by QSO Absorption Lines

Details The Nature and Distribution of Baryons in the Early Universe as Probed by QSO Absorption Lines The Nature and Distribution of Baryons in the Early Universe as Probed by QSO Absorption Lines

Jan 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996phdt.........6f&link_type=abstract

Thesis (PH.D.)--COLUMBIA UNIVERSITY, 1996.Source: Dissertation Abstracts International, Volume: 57-05, Section: B, page: 3249.

Physics

1

Galaxy Formation, Quasars

Scientific paper

In this thesis, I use the absorption toward distant QSOs to study the size and nature of the most common objects in the early universe--the Lyman alpha forest clouds and probe the physical conditions of the diffuse intergalactic medium by measuring the Gunn-Peterson effect. By studying the spectroscopy of closely separated QSOs, we found that Lyalpha clouds are very large at redshifts ~2, with a median radius ~150 h ^{-1}kpc in a (Omega _0,Lambda_0)=(1,0) universe. Their baryonic mass and cosmic overdensity suggest a population of gravitationally bound but unvirialized protogalactic objects at z ~ 2. The comoving volume density, dynamical collapsing timescale, and weak clustering of these clouds suggest that they are possible progenitors of the faint blue galaxies at z ~ 1. Baryons included in the clouds may contain substantial fraction of baryons in the universe. It is indicated that the simple idealization of unclustered, uniform-sized spherical clouds does not accurately describe the Lyalpha cloud population. Distribution of cloud size, clustering, filamentary shape and evolution of cloud size might all be important factors. We have developed a systematic and quantitatively testable and repeatable procedure, in particular, a robust statistical weighting technique for measuring the H I Gunn -Peterson effect at high redshift. We have applied this procedure to Lyalpha forest echelle spectra of a high redshift QSO in both high and low signal -to-noise ratio data, and obtained consistent value of tau_{rm GP} with good accuracy. We have also applied it to a homogeneous QSO absorption line sample to study the redshift dependence of the Gunn-Peterson effect and found the tendency of tauGP increasing with redshift. It was shown that the weighted intensity function analysis can locate the correct local continuum level with good sensitivity in very crowded absorption spectra, and is effective on data with both moderate and high spectral resolution, and can be applied to QSOs with redshift up to 5.

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