The major development in understanding the Lyman

The major development in understanding the Lyman -...

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The major development in understanding the Lyman <α forest (indeed one that almost halted the traditional field, since it weakened the putative connection between the absorbers and protogalaxies) was the understanding (Cen et al. 1997 ApJL 437, L9 and later papers, Levshakov and Kegel 1998 MNRAS 301, 323) that what look spectroscopically like discrete clouds are a natural result of (initially weak) fluctuations in a low-density gas which is subject to perturbation by density effects, including weak shocks. The ionization state as well as velocity structure (just as in flow-induced redshift distortions of clusters and filaments in the galaxy distribution) will be modulated more strongly than the density field. Some of the effect is seen in this neutral hydrogen density contour from a model by Miralda-Escude et al. (1996 ApJ 471, 582, by
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Unformatted text preview: permission of the AAS), which also generated very convincing absorption profiles and statistics. Renyue Cen has an extensive set of simulations available on the Web . As an example, here is a typical perspective view of the H I density in a 25-Mpc comoving cube at z =4 (courtesy of Cen, who gave permission for book usage ). Radio jets and lobes: the existence and structure of radio sources requires some external medium providing a counterpressure, else they would freely expand and become rapidly invisible. General stability and structure considerations allow some limits to be placed on the surrounding medium. Early work includes Rosen and Wiita (1988 ApJ 330, 16); a fuller treatment has been done by Hardee et al. (1992 ApJ 387, 460), with more rapid progress now possible....
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The major development in understanding the Lyman -...

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