MOCCA-SURVEY Database II -- Properties of Intermediate Mass Black Holes
  escaping from star clusters
  In this work we investigate properties of intermediate-mass black holes
(IMBHs) that escape from star clusters due to dynamical interactions. The
studied models were simulated as part of the preliminary second survey carried
out using the MOCCA code (MOCCA-SURVEY Database II), which is based on the
Monte Carlo N-body method and does not include gravitational wave recoil kick
prescriptions of the binary black hole merger product. We have found that IMBHs
are more likely to be formed and ejected in models where both initial central
density and central escape velocities have high values. Most of our studied
objects escape in a binary with another black hole (BH) as their companion and
have masses between $100$ and $140\: M_{\odot}$. Escaping IMBHs tend to
build-up mass most effectively through repeated mergers in a binary with BHs
due to gravitational wave emission. Binaries play a key role in their ejection
from the system as they allow these massive objects to gather energy needed for
escape. The binaries in which IMBHs escape tend to have very high binding
energy at the time of escape and the last interaction is strong but does not
involve a massive intruder. These IMBHs gain energy needed to escape the
cluster gradually in successive dynamical interactions. We present specific
examples of the history of IMBH formation and escape from star cluster models.
We also discuss the observational implications of our findings as well as the
potential influence of the gravitational wave recoil kicks on the process.
