Mathematics – Logic
Scientific paper
May 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aipc..408..303c&link_type=abstract
The ultraviolet universe at low and high redshift. AIP Conference Proceedings, Volume 408, pp. 303-312 (1997).
Mathematics
Logic
Origin And Formation Of The Universe, Characteristics And Properties Of External Galaxies And Extragalactic Objects, Ultraviolet, Quasars
Scientific paper
Quasar spectra contain a record of the history of the gaseous content of the Universe from z=0 to z=5. Key transitions and edges of H, He, and various metals are observable only in the UV from structures over a significant fraction of the age of the Universe. This paper will describe the distribution of gas in the Universe as observed through quasar absorption lines, beginning with the most diffuse gaseous component and proceeding from low to high density enhancements to the gaseous content of galaxies: 1) The most diffuse component has been detected via the He II Gunn Peterson effect, a depression of the quasar continuum shortward of the He II edge (Heap, these Proceedings). In cosmological N-body/hydrodynamic simulations this gas exists in underdense regions, i.e. in ``cosmic mini-voids'' [1]. 2) At high redshifts the Universe appears to be filled with a network of filaments and sheets of H which produce thousands of Lyman-alpha forest absorption lines toward a typical quasar. A combination of high resolution optical spectroscopy of the high redshift forest, HST/FOS spectra of the low redshift forest, and a battery of N-body/hydrodynamic cosmological simulations contributed to the development of a plausible first order picture of structure formation. In this picture, the diffuse gas is gradually evacuating the voids, falling into sheets, moving along filaments, and producing the discrete entities called galaxies. 3) The galaxies themselves are studied as gradually forming and dynamically evolving systems through observations of their H and of a wide range of ionization states of various metals, many accessible only with HST/STIS in the UV (Churchill, this volume). The nature of the very strongest H absorption lines, the damped Lyman-alpha absorbers at high and low redshift, are also discussed since they are being utilized to probe the global history of star formation.
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