Mathematics – Logic
Scientific paper
Dec 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000msngr.102....8c&link_type=abstract
The Messenger, vol. 102, p. 8-12
Mathematics
Logic
1
Scientific paper
1. The Signature of Neutral HI in the High-Redshift Universe The Lyman-a resonance line of neutral hydrogen provides a sensitive probe to study the cosmological distribution of the baryonic matter and the conditions in the intergalactic medium (IGM) over a wide range of redshifts, up to z ~ 6. Observations of the “forest” of Lyman-a absorptions along the lines of sight to quasars, the most luminous objects known, reveal a wealth of structures, ranging from fluctuations of the diffuse IGM to the interstellar medium in protogalactic objects. The properties of the Lyman-a forest at different redshifts constrain the cosmological parameters, such as the density of baryons and the density parameter W, and are the key to issues like the formation of galaxies and large-scale structure, the origin and properties of the ionising radiation background. In particular, it was early recognised by Gunn & Peterson (1965) that, to avoid producing a very large HI opacity at wavelengths just below that of the q u a s a r's Ly m a n-a emission line, a strong photoionisation by the metagalactic UV background is necessary, which at high redshift is produced by the first generation of stars, which also enrich the IGM with metals (also observed in the form of absorptions).
Cristiani Stefano
D'Odorico Sandro
Kim Tae Seong
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