We report on the first ALMA observation of the CO ( 3 - 2 ) and rest-frame \sim 340 GHz continuum emission in PDS 456 , which is the most luminous , radio-quiet QSO in the local Universe ( z \simeq 0.18 ) , with a bolometric luminosity L _ { Bol } \sim 10 ^ { 47 } erg s ^ { -1 } .
ALMA angular resolution allowed us to map scales as small as \sim 700 pc .
The molecular gas reservoir , traced by the core of the very bright CO ( 3 - 2 ) emission line , is distributed in a compact rotating disk , with size of \sim 1.3 kpc , seen close to face-on ( i \sim 25 deg ) .
Fast CO ( 3 - 2 ) emission in the velocity range v \in [ -1000 , 500 ] km s ^ { -1 } is also present .
Specifically , we detect several blue-shifted clumps out to \sim 5 kpc from the nucleus , in addition to a compact ( R \lesssim 1.2 kpc ) , broad emission component .
These components reveal a galaxy-wide molecular outflow , with a total mass M _ { mol } ^ { out } \sim 2.5 \times 10 ^ { 8 } M _ { \odot } ( for an \alpha _ { CO } = 0.8 M _ { \odot } ( K km s ^ { -1 } pc ^ { 2 } ) ^ { -1 } ) and a mass outflow rate \dot { M } _ { mol } \sim 290 M _ { \odot } yr ^ { -1 } .
The corresponding depletion time is \tau _ { dep } \sim 8 Myr , shorter than the rate at which the molecular gas is converted into stars , indicating that the detected outflow is potentially able to quench star-formation in the host .
The momentum flux of the molecular outflow normalised to the radiative momentum output ( i.e . L _ { Bol } / c ) is \lesssim 1 , comparable to that of the X-ray ultra-fast outflow ( UFO ) detected in PDS 456 .
This is at odds with the expectations for an energy-conserving expansion suggested for most of the large-scale outflows detected in low-luminosity AGN so far .
We suggest three possible scenarios that may explain this observation : ( i ) in very luminous AGN such as our target the molecular gas phase is tracing only a fraction of the total outflowing mass ; ( ii ) a small coupling between the shocked gas by the UFO and the host-galaxy ISM ( iii ) AGN radiation pressure may play an important role in driving the outflow .