Small Scale Structure and High Redshift HI

Abstract

Cosmological simulations with gas dynamics suggest that the Lyman-alpha forest is produced mainly by "small scale structure" --- filaments and sheets that are the high redshift analog of today's galaxy superclusters. There is no sharp distinction between Lyman-alpha clouds and "Gunn-Peterson" absorption produced by the fluctuating IGM -- the Lyman-alpha forest {\it is} the Gunn-Peterson effect. Lyman limit and damped Lyman-alpha absorption arises in the radiatively cooled gas of forming galaxies. At $z2-3$, most of the gas is in the photoionized, diffuse medium associated with the Lyman-alpha forest, but most of the {\it neutral} gas is in damped Lyman-alpha systems. We discuss generic evolution of cosmic gas in a hierarchical scenario of structure formation, with particular attention to the prospects for detecting 21cm emission from high redshift HI. A scaling argument based on the present-day cluster mass function suggests that objects with $M_{HI} >~ 5e11 h^{-1} \msun$ should be extremely rare at $z3$, so detections with existing instruments will be difficult. An instrument like the proposed Square Kilometer Array could detect individual damped Lyman-alpha systems at high redshift, making it possible to map structure in the high redshift universe in much the same way that today's galaxy redshift surveys map the local large scale structure.

15 pages, latex w/ crckapb & epsf macros, ps figures; get ps version with all figures from ftp://bessel.mps.ohio-state.edu/pub/dhw/Preprints To appear in Cold Gas at High Redshift, eds. M. Bremer et al. (Kluwer, 1996)

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• Gravitational Collapse of Small-Scale Structure as the Origin of the Lyman Alpha Forest
• From Microwave Anisotropies to Cosmology
• Reheating during Hierarchical Clustering in the Universe Dominated by the Cold Dark Matter
• Spectroscopy of the Double Quasars Q1343+266AB: I. a New Determination of the Size of Lyman-Alpha Forest Absorbers
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Cited by in corpus (3)

• The Statistics of Density Peaks and the Column Density Distribution of the Lyman-Alpha Forest
• Hydrodynamical Simulations of the Lyman Alpha Forest: Model Comparisons
• The broadening of Lyman-alpha forest absorption lines