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We have studied the behaviour of stellar streams in the Aquarius fullycosmological N-body simulations of the formation of Milky Way halos. Inparticular, we have characterised the streams in angle/frequency spaces derivedusing an approximate but generally well-fitting spherical potential. We havealso run several test-particle simulations to understand and guide ourinterpretation of the different features we see in the Aquarius streams. Ourgoal is both to establish which deviations of the expected action-anglebehaviour of streams exist because of the approximations made on the potential,but also to derive to what degree we can use these coordinates to model streamsreliably.  We have found that many of the Aquarius streams wrap in angle space alongrelatively straight lines, and also in frequency space. On the other hand, fromour controlled simulations we have been able to establish that deviations fromspherical symmetry, the use of incorrect potentials and the inclusion ofself-gravity lead to streams in angle space to still be along relativelystraight lines but also to depict wiggly behaviour whose amplitude increases asthe approximation to the true potential becomes worse. In frequency spacestreams typically become thicker and somewhat distorted. Therefore, ouranalysis explains most of the features seen in the approximate angle andfrequency spaces for the Aquarius streams with the exception of their somewhat`noisy' and `patchy' morphologies. These are likely due to the interactionswith the large number of dark matter subhalos present in the cosmologicalsimulations. Since the measured angle-frequency misalignments of the Aquariusstreams can largely be attributed to using the wrong (spherical) potential,determining the mass growth history of these halos will only be feasible oncethe true potential has been determined robustly.

On the behaviour of streams in angle and frequency spaces in different potentials