Testing the evolutionary link between submillimetre galaxies and quasars: CO observations of QSOs atz∼ 2

We have used the IRAM Plateau de Bure millimeter interferometer and the UKIRT 1– 5µm Imager Spectrometer (UIST) to test the connection between the major phases of spheroid growth and nuclear accretion by mapping CO emission in nine submillimetredetected QSOs at z = 1.7–2.6 with black hole (BH) masses derived from near-infrared spectroscopy. When combined with one QSO obtained from the literature, we present sensitive CO(3–2) or CO(2–1) observations of 10 submillimetre-detected QSOs selected at the epoch of peak activity in both QSOs and submillimetre (submm) galaxies (SMGs). CO is detected in 5/6 very optically luminous (MB ∼ −28) submm-detected QSOs with BH masses MBH ≃ 10 9 –10 10 M⊙, confirming the presence of large gas reservoirs of Mgas ≃ 3.4 × 10 10 M⊙. Our BH masses and dynamical mass constraints on the host spheroids suggest, at face value, that these optically luminous QSOs at z = 2 lie about an order of magnitude above the local BH-spheroid relation, MBH/Msph, although