What triggers a radio AGN? The intriguing case of PKSB 1718-649
  We present new Australia Telescope Compact Array (ATCA) observations of the
young (< 10^2 years) radio galaxy PKS B1718-649. We study the morphology and
the kinematics of the neutral hydrogen (HI) disk (M(HI) = 1.1x 10^10 M(sun),
radius ~ 30 kpc). In particular, we focus on the analysis of the cold gas in
relation to the triggering of the nuclear activity. The asymmetries at the
edges of the disk date the last interaction with a companion to more than 1 Gyr
ago. The tilted-ring model of the HI disk shows that this event may have formed
the disk as we see it now, but that it may have not been responsible for
triggering the AGN. The long timescales of the interaction are incompatible
with the short ones of the radio activity. In absorption, we identify two
clouds with radial motions which may represent a population that could be
involved in the triggering of the radio activity. We argue that PKS B1718-649
may belong to a family of young low-excitation radio AGN where, rather than
through a gas rich merger, the active nuclei (AGN) are triggered by local
mechanisms such as accretion of small gas clouds.
