Summary: An Absorbing Workshop

Abstract

After an initial, confusing epoch, in which astronomers disagreed vigorously about the locations of the gas clouds responsible for absorption lines, has come consensus that most, and the most interesting, are distributed through space between us and the source quasars/QSOs, at the distances indicated by their redshifts. Absorption lines thus provide a powerful probe of structure and conditions at redshifts z = 1−4 and beyond that are otherwise largely inaccessible. At least two important ideas crystallized at the workshop. First, categories of lines characterized by different column depths and (apparent) compositions are closely related, at least partly by evolutionary processes. And, second, the structures and conditions that the lines reveal are closely related, again at least partly by evolutionary processes, to the structures and conditions shown by QSOs themselves and by galaxies at smaller redshifts. The sheer richness of recent spectra from HST, Keck, and elsewhere was a third, striking feature.