2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/2042The evolution of Ly-alpha absorber counts is simulated for a model population of absorbing galaxies. The distribution of gas relative to galaxies could evolve between moderate and low redshifts, but constraints are needed on the strength and evolution of the ionizing UV background.2 pages, to appear in Galaxy Disks and Disk GalaxiesAstrophysicstext