G. Gonzalezcasado et al., THE DYNAMICAL SURVIVAL OF SMALL-SCALE SUBSTRUCTURE IN RELAXED GALAXY CLUSTERS, The Astrophysical journal, 433(2), 1994, pp. 120000061-120000064
We consider the dynamical evolution of small-scale substructure in clu
sters within two extreme alternate scenarios for their possible origin
: (1) the accretion of groups (or small clusters) on quasi-radial orbi
ts and (2) the merger of clusters of similar masses, followed by the d
ecoupling of their dense cores. Using simple analytical arguments and
checking with numerical computations, we show that objects are destroy
ed by the tidal field of the global cluster potential if their mean de
nsity is small compared to the mean cluster density within the radius
of closest approach of the group or detached core. Accreted groups and
small clusters are thus tidally disrupted in one cluster crossing. Si
nce the cores of clusters are much denser than groups, they are consid
erably more robust to tides, but the least massive are destroyed or se
verely stripped by tides, while the others are brought to the cluster
center by dynamical friction (and subsequently merge) in less than one
orbit. The longest lived substructures are detached cores, roughly 10
times less massive than the cluster, starting in near-circular orbits
beyond 1 h-1 Mpc from the cluster center.