The gentle monster PDS456 as seen by ALMA: implications for AGN feedback

We present the first ALMA observation of the nearby QSO PDS456 (z=0.185), mapping with unprecedented resolution (~700 pc) the molecular gas in the host-galaxy of a hyper-luminous QSO. With a bolometric luminosity LBol~10^47 erg/s, it can be regarded as the local analogue of the QSOs shining at z~2, i.e. the peak epoch of QSO luminosity density. We report on the discovery of a molecular outflow in PDS456, which also shows the most powerful, persistent, X-ray ultra-fast (0.25c) wind discovered so far. The exquisite ALMA resolution allows us to map this outflow in great detail, revealing a bright compact (R~1.2 kpc) outflow component plus several extended (R~1.3-5 kpc) clumps, characterized by blue-shifted bulk velocities up to -1000 km/s. For the first time, we get new insights on how multi-phase AGN-driven outflows expand outwards in the high-luminosity regime, finding that (i) the molecular gas may represent a minority fraction of the total outflowing gas mass, and (ii) the outflow in PDS456 can be explained as direct radiation-pressure on the ISM clouds or, alternatively, as an energy-conserving expansion with poor-coupling with the ISM