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Published October 20, 2006 | Published
Journal Article Open

CO(1-0) in z ≳ 4 Quasar Host Galaxies: No Evidence for Extended Molecular Gas Reservoirs


We present ^(12)CO(J = 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 Effelsberg 100 m telescope. We detect, for the first time, the CO ground-level transition in BR 1202-0725. For PSS J2322+1944 and APM 08279+5255, our observations result in line fluxes that are consistent with previous NRAO Very Large Array (VLA) observations, but they reveal the full line profiles. We report a typical lensing-corrected velocity-integrated intrinsic ^(12)CO(J = 1 → 0) line luminosity of L'_(CO) = 5 × 10^(10) K km s^(-1) pc^2 and a typical total H_2 mass of M(H_2) = 4 × 10^(10) M_☉ for the sources in our sample. The CO/FIR luminosity ratios of these high-z sources follow the same trend as seen for low-z galaxies, leading to a combined solution of log L_(FIR) = (1.39 ± 0.05) log L_(CO) - 1.76. It has previously been suggested that the molecular gas reservoirs in some quasar host galaxies may exhibit luminous, extended ^(12)CO(J = 1 → 0) components that are not observed in the higher J CO transitions. Using the line profiles and the total intensities of our observations and large velocity gradient (LVG) models based on previous results for higher J CO transitions, we derive that emission from all CO transitions is described well by a single gas component in which all molecular gas is concentrated in a compact nuclear region. Thus, our observations and models show no indication of a luminous extended, low surface brightness molecular gas component in any of the high-redshift QSOs in our sample. If such extended components exist, their contribution to the overall luminosity is limited to at most 30%.

Additional Information

© 2006 American Astronomical Society. Received 2005 October 26; accepted 2006 June 16. The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation. We would like to thank the staff at the GBT, in particular J. Braatz, G. I. Langston, and R. J. Maddalena, for their extensive support and many helpful discussions. D. R. acknowledges support from Deutsche Forschungsgemeinschaft (DFG) Priority Programme 1177. C. C. acknowledges support from the Max-Planck-Gesellschaft and the Alexander von Humboldt-Stiftung through the Max-Planck-Forschungspreis. We thank the referee for many useful comments that helped to improve the manuscript.

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