The role of bars on the dynamical-friction driven inspiral of massive
  perturbers
  In this paper, we systematically explore the impact of a galactic bar on the
inspiral time-scale of a massive object (MO) within a Milky Way-like galaxy. We
integrate the orbit of MOs in a multi-component galaxy model via a
semi-analytical approach that accounts for dynamical friction generalized to
rotationally supported backgrounds. We compare the MO evolution in a galaxy
featuring a Milky Way-like rotating bar to the evolution within an analogous
axisymmetric galaxy without the bar. In agreement with previous studies, we
find that the bar presence may significantly affect the inspiral, sometimes
making it shorter by a factor of a few, sometimes hindering it for a Hubble
time. The erratic behaviour is mainly impacted by the relative phase at which
the MO encounters the stronger bar-induced resonances. In particular, the
effect of the bar is more prominent for initially in-plane, prograde MOs,
especially those crossing the bar co-rotation radius or outer Lindblad
resonance. In the barred galaxy, we find the sinking of the most massive MOs
(>~10^7.5 Msun) approaching the galaxy from large separations (>~8 kpc) to be
most efficiently hampered. Neglecting the effect of global torques associated
with the non-symmetric mass distribution is thus not advisable even within an
idealized, smooth galaxy model; we further note that spiral patterns are
unlikely to affect the inspiral due to their transient and fluctuating nature.
We speculate that the sinking efficiency of massive black holes involved in
minor galaxy mergers may be hampered in barred galaxies, making them less
likely to host a gravitational wave signal accessible to low-frequency
detectors.
