Hydrodynamical Backflow in X-shaped Radio Galaxy PKS 2014-55
  We present MeerKAT 1.28 GHz total-intensity, polarization, and spectral-index
images covering the giant (projected length $l \approx 1.57$~Mpc) X-shaped
radio source PKS~2014$-$55 with an unprecedented combination of brightness
sensitivity and angular resolution. They show the clear "double boomerang"
morphology of hydrodynamical backflows from the straight main jets deflected by
the large and oblique hot-gas halo of the host galaxy PGC~064440. The magnetic
field orientation in PKS~2014$-$55 follows the flow lines from the jets through
the secondary wings. The radio source is embedded in faint ($T_\mathrm{b}
\approx 0.5 \mathrm{\,K}$) cocoons having the uniform brightness temperature
and sharp outer edges characteristic of subsonic expansion into the ambient
intra-group medium. The position angle of the much smaller ($l \sim 25$~kpc)
restarted central source is within $5^\circ$ of the main jets, ruling out
models that invoke jet re-orientation or two independent jets. Compression and
turbulence in the backflows probably produce the irregular and low polarization
bright region behind the apex of each boomerang as well as several features in
the flow with bright heads and dark tails.
