SUPER. VI. A giant molecular halo around a z~2 quasar
  We present the discovery of copious molecular gas in the halo of cid_346, a
$z=2.2$ quasar studied as part of the SINFONI survey for Unveiling the Physics
and Effect of Radiative feedback (SUPER). New Atacama Compact Array (ACA)
CO(3-2) observations detect a much higher flux (by a factor of $14\pm5$) than
measured on kiloparsec scales ($r\lesssim8$ kpc) using previous snapshot
Atacama Large Millimeter/submillimeter Array data. Such additional CO(3-2)
emission traces a structure that extends out to $r\sim200$ kpc in projected
size, as inferred through direct imaging and confirmed by an analysis of the uv
visibilities. This is the most extended molecular circumgalactic medium (CGM)
reservoir that has ever been mapped. It shows complex kinematics, with an
overall broad line profile (FWHM $= 1000$ km/s) that is skewed towards
redshifted velocities up to at least $v\sim1000$ km/s. Using the optically thin
assumption, we estimate a strict lower limit for the total molecular CGM mass
observed by ACA of $M_{mol}^{CGM}>10^{10}~M_{\odot}$. There is however room for
up to $M^{CGM}_{mol}\sim 1.7\times 10^{12}$ $M_{\odot}$, once optically thick
CO emission with $\alpha_{\rm CO}=3.6$ $\rm M_{\odot}~(K~km~s^{-1}~pc^2)^{-1}$
and $L^{\prime}_{CO(3-2)}/L^{\prime}_{CO(1-0)}=0.5$ are assumed. Since cid_346
hosts quasar-driven ionised outflows and since there is no evidence of merging
companions or an overdensity, we suggest that outflows may have played a
crucial rule in seeding metal-enriched, dense gas on halo scales. However, the
origin of such an extended molecular CGM remains unclear.
