Millimeter-wave ( CO ) observations of optically-selected QSOs are potentially a powerful tool for studying the properties of both the QSOs and their host galaxies .
We summarize here a recent molecular gas survey of z < 0.17 optical QSOs with infrared ( IR ) excess , L _ { IR } ( 8 - 1000 \mu { m } ) / L _ { bbb } ( 0.1 - 1.0 \mu { m } ) > 0.36 .
Eight of these QSOs have been detected to date in CO ( 1 \to 0 ) , and the derived molecular gas masses are in the range 1.7 - 35 \times 10 ^ { 9 } M _ { \odot } .
The high L _ { IR } / L ^ { \prime } _ { CO } of QSOs relative to the bulk of the local ( z < 0.2 ) IR luminous galaxy merger population is indicative of significant heating of dust ( L _ { IR } ) by the QSO nucleus and/or by massive stars created in the host galaxy with high efficiency ( i.e. , per unit molecular gas , L ^ { \prime } _ { CO } ) .