On the identification of substructure in phase-space using orbital
  frequencies
  We study the evolution of satellite debris to establish the most suitable
space to identify past merger events. We confirm that the space of orbital
frequencies is very promising in this respect. In frequency space individual
streams can be easily identified, and their separation provides a direct
measurement of the time of accretion. We are able to show for a few idealised
gravitational potentials that these features are preserved also in systems that
have evolved strongly in time. Furthermore, this time evolution is imprinted in
the distribution of streams in frequency space. We have also tested the power
of the orbital frequencies in a fully self-consistent (live) N-body simulation
of the merger between a disk galaxy and a massive satellite. Even in this case
streams can be easily identified and the time of accretion of the satellite can
be accurately estimated.
