L. Lu, A.M. Wolfe, D.A. Turnshek, "The redshift distribution of Lya clouds and the proximity effect," Astrophysical Journal, 367:19-36, 1991.

Limin Lu (Washburn Observatory, University of Wisconsin, Madison): "Lyman-a clouds are clumps of gaseous material distributed between galaxies and probably contain primordial matter that has not been chemically enriched. These clouds can be used to study the intergalactic medium in the universe between now and when the universe was only about 10 percent of its current age! Knowledge of Lyman-a clouds may also shed light on galaxy formation and evolution.

"We confirmed a previous result that the clouds evolve rapidly: There are far more Lyman-a clouds in the early universe than any reasonable cosmological model can accommodate without invoking changes in the intrinsic properties of these clouds. Moreover, we demonstrated that there are relatively fewer Lyman-a clouds near quasars, because of the energetic photons from the quasar. This is significant,...

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