Major Mergers of Galaxy Haloes: Cuspy or Cored Inner Density Profile?
Abstract
We present the results from a series of collisionless N-body simulations of major mergers of galaxy dark matter haloes with density profiles having either inner cusps or cores. Our simulations range from 2x10^5 to 10^7 particles, allowing us to probe the phase-space distribution of dark matter particles in the innermost regions (less than 0.005 virial radii) of CDM haloes, a subject of much recent debate. We find that a major merger of two cored haloes remains cored and does not result in a cuspy profile seen in many cosmological simulations. Mergers of a cuspy halo with either a cored halo or a second cuspy halo of equal mass, on the other hand, produce cuspy haloes with a slightly reduced inner logarithmic slope. Cuspy haloes, once formed, therefore appear resilient to major mergers. We find the velocity structure of the remnants to be mildly anisotropic, with a Maxwellian velocity distribution near the centre but not in the outer portions of the final haloes. Violent relaxation is effective only during the early phase of mergers, with phase mixing likely to be the dominant relaxation process at late times.Keywords
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