The chemical footprint of AGN feedback in the outflowing circumnuclear
  disk of NGC 1068
  In the nearby (D=14 Mpc) AGN-starburst composite galaxy NGC 1068, it has been
found that the molecular gas in the Circum-nuclear Disk (CND) is outflowing,
which is a manifestation of ongoing AGN feedback. The outflowing gas has a
large spread of velocities, which likely drive different shock chemistry
signatures at different locations in the CND. We perform a multi-line molecular
study using two shock tracers, SiO and HNCO, with the aim to determine the gas
properties traced by these two species, and explore the possibility of
reconstructing the shock history in the CND. Five SiO transitions and three
HNCO transitions were imaged at high resolution $0''.5-0''.8$ with the Atacama
Large Millimeter/submillimeter Array (ALMA). We performed both LTE and non-LTE
radiative transfer analysis coupled with Bayesian inference process in order to
characterize the gas properties, such as molecular gas density and gas
temperature. We found clear evidence of chemical differentiation between SiO
and HNCO, with the SiO/HNCO ratio ranging from greater than one on the east of
CND to lower than one on the west side. The non-LTE radiative transfer analysis
coupled with Bayesian inference confirms that the gas traced by SiO has
different densities - and possibly temperatures - than that traced by HNCO. We
find that SiO traces gas affected by fast shocks while the gas traced by HNCO
is either just affected by slow shocks or not shocked at all. A distinct
differentiation between SiO and HNCO has been revealed in our observations and
the further analysis of the gas properties traced by both species, which
confirms the results from previous chemical modelings.
