  We present a comparative study of recent works on merger-timescales with
dynamical friction and find a strong contrast between idealized/isolated
mergers (Boylan-Kolchin et al. 2008) and mergers from a cosmological volume
(Jiang et al. 2008). 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. (2008) 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.
