paper

Gravitational Collapse of Small-Scale Structure as the Origin of the Lyman Alpha Forest

arXiv:astro-ph/9409017 · doi:10.1086/187670

Abstract

If gravitational clustering is a hierarchical process, the present large-scale structure of the galaxy distribution implies that structures on smaller scales must have formed at high redshift. We simulate the formation of small-scale structure (average cell mass: M) and the evolution of photoionized gas, in the specific case of a CDM model with a cosmological constant. The photoionized gas has a natural minimal scale of collapse, the Jeans scale (M). We find that low column density ($\nhi \le 10^{14}\cm^{-2}$) lines originate in regions resembling Zel'dovich pancakes, where gas with overdensities in the range is enclosed by two shocks but is typically re-expanding at approximately the Hubble velocity. However, higher column density ($\nhi \ge 10^{15}\cm^{-2}$) lines stem from more overdense regions where the shocked gas is cooling. We show that this model can probably account for the observed number of lines, their distribution in column density and b-parameters, as well as the cloud physical sizes as observed in gravitationally lensed quasars. We find a redshift evolution that is

15p postscript file to appear in The Astrophysical Journal Letters (1994)

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