  We discuss the merging rates in compact groups of 5 identical elliptical
galaxies. All groups have the same mass and binding energy. We consider both
cases with individual halos and cases where the halo is common to all galaxies
and enveloping the whole group. In the latter situation the merging rate is
slower if the halo is more massive. The mass of individual halos has little
influence on the merging rates, due to the fact that all galaxies in our
simulations have the same mass, and so the more extended ones have a smaller
velocity dispersion. Groups with individual halos merge faster than groups with
common halos if the configuration is centrally concentrated, like a King
distribution of index 10. On the other hand for less concentrated
configurations the merging is initially faster for individual halo cases, and
slower after part of the group has merged. In cases with common halo, centrally
concentrated configurations merge faster for high halo-to-total mass ratios and
slower for low halo-to-total mass ratios. Groups whose virial ratio is
initially less than one merge faster, while groups that have initially
cylindrical rotation merge slower than groups starting in virial equilibrium.
In order to test how long a virialised group can survive before merging we
followed the evolution of a group with a high halo-to-total mass ratio and a
density distribution with very little central concentration. We find that the
first merging occurred only after a large number of crossing times, which with
areasonable calibration should be larger than a Hubble time. Hence, at least
for appropriate initial conditions, the longevity of compact groups is not
necessarily a problem, which is an alternative explanation to why we observe so
many compact groups despite the fact that their lifetimes seem short.
