Detection of HCN, HCO+ and HNC in the Mrk231 molecular outflow - Dense
  molecular gas in the AGN wind
  We detect luminous emission from HCN, HCO+ and HNC 1--0 in the QSO ULIRG
Mrk~231 with the IRAM Plateau de Bure Interferometer at 1."55 by 1."28
resolution. All three lines show broad line wings - which are particularly
prominent for HCN. Velocities are found to be similar (750 km/s) to those found
for CO 1-0. This is the first time bright HCN, HCO+ and HNC emission has been
detected in a large-scale galactic outflow. We find that both the blue- and
red-shifted line wings are spatially extended by at least 0."75 (700 pc) in a
north-south direction. The line wings are brighter (relative to the line center
intensity) in HCN than in CO 1-0 and line ratios suggest that the molecular
outflow consists of dense (n>10E4 cmE-3) and clumpy gas with a high HCN
abundance X(HCN)>10E-8. These properties are consistent with the molecular gas
being compressed and fragmented by shocks in the outflow. Alternatively, HCN is
instead pumped by mid-IR continuum, but we propose that this effect is not
strong for the spatially extended outflowing gas. In addition, we find that the
rotation of the main disk, in east-west direction, is also evident in the HCN,
HCO+ and HNC line emission. An unexpectedly bright HC3N 10-9 line is detected
inside the central 400 pc of Mrk231. This HC3N emission may emerge from a
shielded, dust-enshrouded region within the inner 40-50 pc where the gas is
heated to high temperatures (200 - 300 K) by the AGN.
