Detecting Low-Order CO Emission from z ≳ 4 Quasar Host Galaxies

Molecular gas has now been detected in 15 z>2 QSOs. These detections are commonly obtained by observing high-J CO transitions due to their relatively high peak fluxes and observing frequencies in the millimeter atmospheric windows. However, only observations of the CO ground-state transition, CO(1-0), have the potential to trace the molecular gas at lower excitations, which may give a better estimate of the total molecular gas mass of high-z QSOs. Here we present first z>4 CO(1-0) observations obtained with the NRAO Green Bank Telescope and the MPIfR Effelsberg telescope (Riechers et al. 2006). With these two 100m telescopes, we detect the CO(1-0) transition in the high-redshift QSOs BR 1202-0725 (z = 4.7), PSS J2322+1944 (z = 4.1), and APM 08279+5255 (z = 3.9). We find that the CO/FIR luminosity ratios of these high-z sources follow the same trend as seen for low-z galaxies. Utilizing large velocity gradient (LVG) models based on previous results for higher-J CO transitions, we derive that all CO emission can be described by a single gas component and that all molecular gas appears to be concentrated in a compact nuclear region. We thus find no evidence for luminous, extended CO(1-0) components in the molecular gas reservoirs around our target quasars.