We report the detection of the CO J = 1 - 0 emission line in [ H89 ] 1821+643 , one of the most optically luminous QSOs in the local Universe and a template ULIRG-to-QSO transition object , located in a rich cool-core cluster at z = 0.297 .
The CO emission is likely to be extended , highly asymmetric with respect to the center of the host elliptical where the QSO resides , and corresponds to a molecular gas mass of \sim 8.0 \times 10 ^ { 9 } M _ { \odot } .
The dynamical mass enclosed by the CO line emission region could amount up to \sim 1.7 \times 10 ^ { 12 } M _ { \odot } ( 80 % of the total mass of the elliptical host ) .
The bulk of the CO emission is located at \sim 9 kpc south-east from the nuclei position , and close to a faint optical structure , suggesting that the CO emission could either represent a gas-rich companion galaxy merging with the elliptical host or a tail-like structure reminiscent of a previous interaction .
We argue that the first scenario is more likely given the large masses implied for the CO source , which would imply a highly asymmetric elliptical host .
The close alignment between the CO emission major axis and the radio-plume suggests a possible role of the latter excitation of the ambient gas reservoir .
The stacking technique was used to search for CO emission and 3mm continuum emission from galaxies in the surrounding cluster , however no detection was found either toward individual galaxies or the stacked ensemble of galaxies , with a 3 \sigma limit of < 1.1 \times 10 ^ { 9 } M _ { \odot } for the molecular gas .