Observational signatures of feedback in QSO absorption spectra
  Models for the formation of galaxies and clusters of galaxies require strong feedback in order to explain the observed properties of these systems. We investigate whether such feedback has observational consequences for the intergalactic medium, as probed in absorption towards background quasars. A typical quasar sight-line intersects one proto-cluster per unit redshift, and significant feedback from forming galaxies or AGN, heating the proto-cluster gas, will result in a large clearing of reduced absorption in the Lyman alpha-forest. Such a gap could be detected at redshift > 3 when the mean opacity is high. Feedback from Lyman-break galaxies in proto-clusters can be probed by the absorption lines produced in their winds. Strong feedback from galaxies has a major impact on the number and properties of absorption lines with neutral hydrogen column densities of 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. Galactic winds from dwarf galaxies should break-up into clouds, in order not to over produce the number of absorption lines. These clouds can then coast to large distances. 
Tom Theuns (1,2), H. J. Mo (2) and Joop Schaye (1) ((1) Institute of   Astronomy, Cambridge, (2) Max-Planck Institute, Garching)