Detection of helicoidal motion in the optical jet of PKS 0521-365
  The jet activity of Active Galactic Nuclei (AGN), and its interaction with
the interstellar medium (ISM), may play a pivotal role in the processes which
regulate the growth and star formation of its host galaxy. Observational
evidence which pinpoints the conditions of such interaction is paramount to
unveil the physical processes involved. We report on the discovery of extended
emission line regions exhibiting an S-shaped morphology along the optical jet
of the radio-loud AGN $\text{PKS}\,0521-365$ ($z=0.055$), by using long-slit
spectroscopic observations obtained with FORS2 on VLT. The velocity pattern
derived from the $\text{[O II]}\,\lambda 3727\,\AA,\, \text{H}\beta\, \lambda
4861\,\AA\,$ and [O III] $\lambda\lambda4959,5007\,\AA\,$ emission lines is
well-fitted by a sinusoidal function of the form: $v(r)=\alpha r^{1/2}sin(\beta
r^{1/2}+\gamma)$, suggesting helicoidal motions along the jet up to distances
of $20\,\text{kpc}$. We estimate a lower limit for the mass of the outflowing
ionized gas along the jet of $\sim$10$^4\,M_\odot$. Helical magnetic fields and
jet precession have been proposed to explain helicoidal paths along the jet at
pc scales; nevertheless, it is not clear yet whether these hypotheses may hold
at kpc scales.
