Molecular gas in infrared ultraluminous QSO hosts

We report CO detections in 17 out of 19 infrared ultraluminous QSO (IR QSO) hosts observed with the IRAM 30 m telescope. The cold molecular gas reservoir in these objects is in a range of (0.2-2.1) × 1010 M ⊙ (adopting a CO-to-H2 conversion factor αCO = 0.8 M ⊙ (K km s-1 pc 2)-1). We find that the molecular gas properties of IR QSOs, such as the molecular gas mass, star formation efficiency (L FIR/L′CO), and CO (1-0) line widths, are indistinguishable from those of local ultraluminous infrared galaxies (ULIRGs). A comparison of low- and high-redshift CO-detected QSOs reveals a tight correlation between L FIR and L′CO(1-0) for all QSOs. This suggests that, similar to ULIRGs, the far-infrared emissions of all QSOs are mainly from dust heated by star formation rather than by active galactic nuclei (AGNs), confirming similar findings from mid-infrared spectroscopic observations by Spitzer. A correlation between the AGN-associated bolometric luminosities and the CO line luminosities suggests that star formation and AGNs draw from the same reservoir of gas and there is a link between star formation on kpc scale and the central black hole accretion process on much smaller scales. © 2012. The American Astronomical Society. All rights reserved.