  We derived the evolution of the energy deposition in the intergalactic medium
(IGM) by different decaying (or annihilating) dark matter (DM) candidates.
Heavy annihilating DM particles (with mass larger than a few GeV) have no
influence on reionization and heating, even if we assume that all the energy
emitted by annihilations is absorbed by the IGM. In the case of lighter
particles, the impact on reionization and heating depends on the efficiency of
energy absorption by the IGM. We calculated the fraction of energy produced by
decays and annihilations which is effectively absorbed by the IGM. We found
that this fraction is generally high at very high redshift (>>100), but drops
at more recent epochs.
