Enhanced UV radiation and dense clumps in Mrk231's molecular outflow
  We present interferometric observations of the CN(1-0) line emission in
Mrk231 and combine them with previous observations of CO and other H$_2$ gas
tracers to study the physical properties of the massive molecular outflow. We
find a strong boost of the CN/CO(1-0) line luminosity ratio in the outflow,
which is unprecedented compared to any other known Galactic or extragalactic
source. For the dense gas phase in the outflow traced by the HCN and CN
emissions, we infer $\rm X_{\rm CN}\equiv [CN]/[H_2] > X_{\rm HCN}$ by at least
a factor of three, with H$_2$ gas densities of $n_{\rm H_2}\sim10^{5-6}$
cm$^{-3}$. In addition, for the first time, we resolve narrow spectral features
in the HCN(1-0) and HCO$^+$(1-0) high-velocity line wings tracing the dense
phase of the outflow. The velocity dispersions of these spectral features,
$\sigma_v\sim7-20$ km s$^{-1}$, are consistent with those of massive
extragalactic giant molecular clouds detected in nearby starburst nuclei. The
H$_2$ gas masses inferred from the HCN data are quite high,
$M_{mol}\sim0.3-5\times10^8$ $M_{\odot}$. Our results suggest that massive,
denser molecular gas complexes survive embedded into the more diffuse H$_2$
phase of the outflow, and that the chemistry of such outflowing dense clouds is
affected by enhanced UV radiation.
