2012A&A...537A..44A

Our goal is to study gas properties in large-scale molecular outflows and winds from active galactic nuclei (AGNs) and starburst galaxies. We obtained high-resolution (1.55"x1.28") observations of HCN, HCO⁺, HNC 1-0 and HC₃N 10-9 of the ultraluminous galaxy (ULIRG) Mrk 231 with the IRAM Plateau de Bure Interferometer. We detect luminous emission from HCN, HCO⁺ and HNC 1-0 in the QSO ULIRG Mrk 231. All three lines show broad line wings - which are particularly prominent for HCN. Velocities are found to be similar (≃±750km/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" (>700pc) 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>10⁴cm^–3) and clumpy gas with a high HCN abundance X(HCN)>10^–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 400pc of Mrk 231. 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 (200-300K) by the AGN.