Lyman absorption lines in quasar spectra: evidence for gravitationally-confined gas in dark minihaloes

Primordial gas photoionized by a UV background can be gravitationally confined, in stable equilibrium, by minihaloes of dark matter with virial velocities $$\sim\,30\,\text{km}\,\text{s}^{-1}$$ which are an inevitable concomitant of the cold dark matter cosmogony. The calculated properties of these clouds suggest that they could account for the forest of Lyman absorption lines found in the spectra of high-z quasars.