A significant fraction of extended radio sources presents a peculiar X-shaped
radio morphology: in addition to the classical double lobed structure, radio
emission is also observed along a second axis of symmetry in the form of
diffuse wings or tails. We re-examine the origin of these extensions relating
the radio morphology to the properties of their host galaxies. The orientation
of the wings shows a striking connection with the structure of the host galaxy
as they are preferentially aligned with its minor axis. Furthermore, wings are
only observed in galaxies of high projected ellipticity. Hydrodynamical
simulations of the radio-source evolution show that X-shaped radio-sources
naturally form in this geometrical situation: as a jet propagates in a
non-spherical gas distribution, the cocoon surrounding the radio-jets expands
laterally at a high rate producing wings of radio emission, in a way that is
reminiscent of the twin-exhaust model for radio-sources.Comment: 7 pages, 6 figures, 1 table, accepted for publication in A&
