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Keywords:

  • galaxies: evolution;
  • galaxies: kinematics and dynamics;
  • dark matter

ABSTRACT

We present a comparative study of recent works on merger time-scales with dynamical friction and find a strong contrast between idealized/isolated mergers and mergers from a cosmological volume. Our study measures the duration of mergers in a cosmological N-body simulation of dark matter, with emphasis on higher redshifts (z≤ 10) and a lower mass range. In our analysis we consider and compare two merger definitions: tidal disruption and coalescence. We find that the merger-time formula proposed by Jiang et al. describes our results well and conclude that cosmologically motivated merger-time formulae provide a more versatile and statistically robust approximation for practical applications such as semi-analytic/hybrid models.