CO(1–0) inz≳ 4 Quasar Host Galaxies: No Evidence for Extended Molecular Gas Reservoirs

We present CO(1-0) observations of the high-redshift quasi-stellar objects(QSOs) BR 1202-0725 (z=4.69), PSS J2322+1944 (z=4.12), and APM 08279+5255(z=3.91) using the NRAO Green Bank Telescope (GBT) and the MPIfR Effelsberg100m telescope. We detect, for the first time, the CO ground-level transitionin BR 1202-0725. For PSS J2322+1944 and APM 08279+5255, our observations resultin line fluxes that are consistent with previous NRAO Very Large Array (VLA)observations, but they reveal the full line profiles. We report a typicallensing-corrected velocity-integrated intrinsic CO(1-0) line luminosity ofL'(CO) = 5 x 10^10 K km/s pc^2 and a typical total H_2 mass of M(H2) = 4 x10^10 M_sun for the sources in our sample. The CO/FIR luminosity ratios ofthese high-z sources follow the same trend as seen for low-z galaxies, leadingto a combined solution of log(L_FIR) = (1.39 +/- 0.05) x log(L(CO))-1.76. Ithas previously been suggested that the molecular gas reservoirs in some quasarhost galaxies may exhibit luminous, extended CO(1-0) components that are notobserved in the higher-J CO transitions. Utilizing the line profiles and thetotal intensities of our observations and large velocity gradient (LVG) modelsbased on previous results for higher-J CO transitions, we derive that emissionfrom all CO transitions is described well by a single gas component where allmolecular gas is concentrated in a compact nuclear region. Thus, ourobservations and models show no indication of a luminous extended, low surfacebrightness molecular gas component in any of the high-redshift QSOs in oursample. If such extended components exist, their contribution to the overallluminosity is limited to at most 30%.Comment: 12 pages, 5 figures, 3 tables, to appear in ApJ (accepted June 16, 2006