  The evolution of planets, stars and even galaxies is driven, to a large
extent, by dynamical friction of gravitational origin. There is now a good
understanding of the friction produced by extended media, either collisionless
of fluid-like. However, the physics of accretion or protoplanetary disks, for
instance, is described by slab-like geometries instead, compact in one spatial
direction. Here, we find, for the first time, the gravitational wake due to a
massive perturber moving through a slab-like medium, describing e.g. accretion
disks with sharp transitions. We show that dynamical friction in such
environments can be substantially reduced relatively to spatially extended
profiles. Finally, we provide simple and accurate expressions for the
gravitational drag force felt by the perturber, in both the subsonic and
supersonic regime.
