ALMA observations of PKS 1549-79: a case of feeding and feedback in a
  young radio quasar
  We present CO(1-0) and CO(3-2) ALMA observations of the molecular gas in PKS
1549-79, as well as mm and VLBI 2.3-GHz continuum observations of its radio
jet. PKS 1549-79 is one of the closest young, radio-loud quasars caught in an
on-going merger in which the AGN is in the first phases of its evolution. We
detect three structures tracing the accretion and the outflow of molecular gas:
kpc-scale tails of gas accreting onto PKS 1549-79, a circumnuclear disc (CND)
in the inner few hundred parsec, and a very broad (>2300 \kms) component
detected in CO(1-0) at the position of the AGN. Thus, in PKS 1549-79 we see the
co-existence of accretion and the ejection of gas. The line ratio
CO(1-0)/CO(3-2) suggests that the gas in the CND has both high densities and
high kinetic temperatures. We estimate a mass outflow rate of at least 650
msun/yr. This massive outflow is confined to r < 120 pc, which suggests that
the AGN drives the outflow. Considering the amount of molecular gas available
in CND and the observed outflow rate, we estimate a time scale of ~10^5 yr over
which the AGN would be able to destroy the CND, although gas from the merger
may come in from larger radii, rebuilding this disc at the same time. The AGN
appears to self-regulate gas accretion onto the super-massive black hole. From
a comparison with HST data, we find that the ionised gas outflow is more
extended. Nevertheless, the warm outflow is about two orders of magnitude less
massive than the molecular outflow. PKS 1549-79 does not seem to follow the
scaling relation between bolometric luminosity and the relative importance of
warm ionised and molecular outflows claimed to exist for other AGN. We argue
that, although PKS 1549-79 hosts a powerful quasar nucleus and an ultra-fast
outflow, the radio jet plays a significant role in producing the outflow.
