Molecular outflow and feedback in the obscured Quasar XID2028 revealed
  by ALMA
  We imaged with ALMA and ARGOS/LUCI the molecular gas and the dust and stellar
continuum in XID2028, an obscured QSO at z=1.593, where the presence of a
massive outflow in the ionized gas component traced by the [O III]5007 emission
has been resolved up to 10 kpc. This target represents a unique test case to
study QSO 'feedback in action' at the peak epoch of AGN-galaxy coevolution. The
QSO has been detected in the CO(5-4) transition and in the 1.3mm continuum, at
~30 and ~20 {\sigma} significance respectively, with both emissions confined in
the central (<4 kpc) radius area. Our analysis suggests the presence of a fast
rotating molecular disc (v~400 km/s) on very compact scales, and well inside
the galaxy extent seen in the rest-frame optical light (~10 kpc, as inferred
from the LUCI data). Adding available measurements in additional two CO
transitions, CO(2-1) and CO(3-2), we could derive a total gas mass of
~10$^{10}$ M$_\odot$, thanks to a critical assessment of CO excitation and the
comparison with Rayleigh-Jeans continuum estimate. This translates into a very
low gas fraction (<5%) and depletion time scales of 40-75 Myr, reinforcing the
result of atypical gas consumption conditions in XID2028, possibly due to
feedback effects on the host galaxy. Finally, we also detect at ~5{\sigma} the
presence of high velocity CO gas, which we interpret as a signature of
galaxy-scale molecular outflow, spatially coincident with the ionised gas
outflow. XID2028 represents therefore a unique case where the measurement of
total outflowing mass (~500-800 M$_\odot$/yr) including the molecular and
atomic components, in both the ionised and neutral phases, has been attempted
for a high-z QSO.
