  Motivated by the discovery of a number of radio relics we investigate the
fate of fossil radio plasma during a merger of clusters of galaxies using
cosmological smoothed-particle hydrodynamics simulations. Radio relics are
extended, steep-spectrum radio sources that do not seem to be associated with a
host galaxy. One proposed scenario whereby these relics form is through the
compression of fossil radio plasma during a merger between clusters. The
ensuing compression of the plasma can lead to a substantial increase in
synchrotron luminosity and this appears as a radio relic. Our simulations show
that relics are most likely to be found at the periphery of the cluster at the
positions of the outgoing merger shock waves. Relics are expected to be very
rare in the centre of the cluster where the life time of relativistic electrons
is short and shock waves are weaker than in the cooler, peripheral regions of
the cluster. These predictions can soon be tested with upcoming low-frequency
radio telescopes.
