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 Physicsand Effect of Radiative feedback (SUPER). New Atacama Compact Array (ACA)CO(3-2) observations detect a much higher flux (by a factor of $14\pm5$) thanmeasured on kiloparsec scales ($r\lesssim8$ kpc) using previous snapshotAtacama Large Millimeter/submillimeter Array data. Such additional CO(3-2)emission traces a structure that extends out to $r\sim200$ kpc in projectedsize, as inferred through direct imaging and confirmed by an analysis of the uvvisibilities. This is the most extended molecular circumgalactic medium (CGM)reservoir that has ever been mapped. It shows complex kinematics, with anoverall broad line profile (FWHM $= 1000$ km/s) that is skewed towardsredshifted velocities up to at least $v\sim1000$ km/s. Using the optically thinassumption, we estimate a strict lower limit for the total molecular CGM massobserved by ACA of $M_{mol}^{CGM}>10^{10}~M_{\odot}$. There is however room forup to $M^{CGM}_{mol}\sim 1.7\times 10^{12}$ $M_{\odot}$, once optically thickCO 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_346hosts quasar-driven ionised outflows and since there is no evidence of mergingcompanions or an overdensity, we suggest that outflows may have played acrucial rule in seeding metal-enriched, dense gas on halo scales. However, theorigin of such an extended molecular CGM remains unclear.