We derive the evolution of the energy deposition in the intergalactic medium (IGM) by dark matter (DM) decays/annihilations for both sterile neutrinos and light dark matter (LDM) particles. At z > 200 sterile neutrinos transfer a fraction fabs ∼ 0.5 of their rest mass energy into the IGM; at lower redshifts this fraction becomes < ∼ 0.3 depending on the particle mass. The LDM particles can deca...

The last few years have seen a dramatic improvement in our understanding of the origin of Lyman α absorption systems. Hydrodynamic numerical simulations of cold dark matter dominated universes have shown that the many properties of the Lyman α absorption systems can be explained by a photoionized, space-filling, intergalactic medium. Lyman α lines offer promising probes of the photoionizing bac...

The cocoons surrounding powerful radio sources can be extensive if the jet that feeds the cocoon is light and supersonic. They have been shown to remain overpressured with respect to the ambient medium for most of the life time of the sources. The observed lobes of the radio sources form parts of these extensive cocoons. We show that observations of the lobes of giant radio sources allow one to...