Modelling galaxy merger time-scales and tidal destruction

We present a model for the dynamical evolution of subhaloes based on an approach combining numerical and analytical methods. Our method is based on tracking subhaloes in an N-body simulation up to the latest epoch that it can be resolved, and applying an analytic prescription for its merger time-scale that takes dynamical friction and tidal disruption into account. When applied to cosmological N-body simulations with mass resolutions that differ by two orders of magnitude, the technique produces halo occupation distributions that agree to within 3 per cent. This model has now been implemented in the GALFORM semi-analytic model of galaxy formation.