We present interferometric observations of the CN ( 1-0 ) line emission in Mrk 231 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 X _ { CN } \equiv [ CN ] / [ H _ { 2 } ] > X _ { HCN } by at least a factor of three , with H _ { 2 } gas densities of n _ { H _ { 2 } } \sim 10 ^ { 5 - 6 } \leavevmode \nobreak 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 } \sim 7 - 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 } \sim 0.3 - 5 \times 10 ^ { 8 } \leavevmode \nobreak 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 .