The haloes of merger remnants |
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Authors: | P J McMillan E Athanassoula W Dehnen |
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Institution: | Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH;LAM, Observatoire Astronomique de Marseille Provence, 2 Place Le Verrier, F-13248 Marseille Cedex 4, France;Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford OX1 3NP |
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Abstract: | We perform collisionless N -body simulations of 1:1 galaxy mergers, using models which include a galaxy halo, disc and bulge, focusing on the behaviour of the halo component. The galaxy models are constructed without recourse to a Maxwellian approximation. We investigate the effect of varying the galaxies' orientation, their mutual orbit and the initial velocity anisotropy or cusp strength of the haloes upon the remnant halo density profiles and shape, as well as on the kinematics. We observe that the halo density profile (determined as a spherical average, an approximation we find appropriate) is exceptionally robust in mergers, and that the velocity anisotropy of our remnant haloes is nearly independent of the orbits or initial anisotropy of the haloes. The remnants follow the halo anisotropy – local density slope (β–γ) relation suggested by Hansen & Moore in the inner parts of the halo, but β is systematically lower than this relation predicts in the outer parts. Remnant halo axis ratios are strongly dependent on the initial parameters of the haloes and on their orbits. We also find that the remnant haloes are significantly less spherical than those described in studies of simulations which include gas cooling. |
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Keywords: | methods: N-body simulations galaxies: haloes galaxies: interactions galaxies: kinematics and dynamics |
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