  In this paper, we explore the impact of a galactic bar on the inspiral
time-scale of a massive perturber (MP) within a Milky Way-like galaxy. We
integrate the orbit of MPs in a multi-component galaxy model via a
semi-analytical approach including an accurate treatment for dynamical friction
generalized to rotationally supported backgrounds. We compare the MP evolution
in a galaxy featuring a Milky Way-like rotating bar to the evolution within an
analogous axisymmetric galaxy without the bar. 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, implying that dynamical
friction alone is greatly insufficient to fully characterize the orbital decay.
The effect of the bar is more prominent for initially in-plane, prograde MPs,
especially those crossing the bar co-rotation radius or outer Lindblad
resonance. In the barred galaxy, we find the sinking of the most massive MPs
(>~10^7.5 Msun) approaching the galaxy from large separations (>~8 kpc) to be
most efficiently hampered. Neglecting the effect of global torques associated
to the non-symmetric mass distribution is thus not advisable even within our
idealized, smooth Milky Way model, and it should be avoided when dealing with
more complex and realistic galaxy systems. This has important implications for
the orbital decay of massive black holes in late-type spirals, the natural
candidate sources to be detected with the Laser Interferometer Space Antenna
(LISA).
