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Satellite decay in flattened dark matter haloes

2002; Oxford University Press; Volume: 333; Issue: 4 Linguagem: Inglês

10.1046/j.1365-8711.2002.05414.x

1365-2966

Jorge Peñarrubia, Pavel Kroupa, C. M. Boily,

Dark Matter and Cosmic Phenomena

We carry out a set of self-consistent N-body calculations to compare the decay rates of satellite dwarf galaxies orbiting a disc galaxy embedded in a dark matter halo (DMH). We consider both spherical and oblate axisymmetric DMHs of aspect ratio qh=0.6. The satellites are given different initial orbital inclinations, orbital periods and mass. The live flattened DMHs with embedded discs and bulges are set-up using a new fast algorithm due to Boily, Kroupa & Peñarrubia called magalie. We find that the range of survival times of satellites within a flattened DMH becomes ∼100 per cent larger than the same satellites within a spherical DMH. In the oblate DMH, satellites on polar orbits have the longest survival time, whereas satellites on coplanar prograde orbits are destroyed most rapidly. The orbital plane of a satellite tilts as a result of anisotropic dynamical friction, causing the satellite's orbit to align with the plane of symmetry of the DMH. Polar orbits are not subjected to alignment. Therefore the decay of a satellite in an axisymmetric DMH may provide a natural explanation for the observed lack of satellites within 0–30° of their host galaxy's disc. The computations furthermore indicate that the evolution of the orbital eccentricity e is dependent on its initial value e(t=0) and the DMH's shape. We also discuss some implications of flattened DMHs for satellite debris streams.