Observational signatures of feedback in QSO absorption spectra

Models for the formation of galaxies and clusters of galaxies require stron g feedback in order to explain the observed properties of these systems. We investigate whether such feedback has observational consequences for the i ntergalactic medium, as probed in absorption towards background quasars. A typical quasar sight-line intersects one protocluster per unit redshift, an d significant feedback from forming galaxies or active galactic nuclei, hea ting the protocluster gas, will result in a large clearing of reduced absor ption in the Ly alpha forest. Such a gap could be detected at redshift grea ter than or similar to3 when the mean opacity is high. Feedback from Lyman- break galaxies in protoclusters can be probed by the absorption lines produ ced in their winds. Strong feedback from galaxies has a major impact on the number and properties of absorption lines with column densities N-H I simi lar to 10(16) cm(-2). This feedback can be probed with multiple sight-lines and by studying the unsaturated higher order lines of the Lyman series. Ga lactic winds from dwarf galaxies should break up into clouds, in order not to overproduce the number of absorption lines. These clouds can then coast to large distances.