  Some X-shaped radio galaxies show a Z-symmetric morphology in the less
luminous secondary lobes. Within the scenario of a merger between two galaxies,
each hosting a supermassive black hole in its center, this structure has been
explained before: As the smaller galaxy spirals towards the common center, it
releases gas to the ISM of the larger active galaxy. The ram pressure of this
streaming gas will bend the lobes of the pre-merger jet into a Z-shape. After
the black holes have merged the jet propagates in a new direction that is
aligned with the angular momentum of the binary black hole. In this article we
deproject the pre- and post-merger jets. Taking into account the expected
angles between the jet pairs and with the assumption that their directions are
uncorrelated, we show that one of three possible orientations of the jets with
respect to the line of sight is more likely than the others. This actually
depends on the distance where the bending occurs. Another result of our
deprojection is that the streaming gas bends the jet into a Z-shape in a range
between about 30 and 100 kpc distance to the center of the primary galaxy. We
confirm this finding by comparing our predictions for the properties of the
rotational velocity field and its radius with observations and numerical
simulations of merging galaxies. Thus our results support the merger scenario
as explanation for X- and Z-shaped radio galaxies with the jet pointing along
the former axis of orbital angular momentum of the binary.
