Molecular Gas in Infrared Ultraluminous QSO Hosts

TL;DR

This study detects molecular gas in infrared ultraluminous QSOs, showing their properties are similar to local ULIRGs and indicating star formation primarily powers their infrared emission, with a link to black hole activity.

Contribution

First comprehensive CO detection in IR QSOs demonstrating their molecular gas properties are akin to ULIRGs and establishing a connection between star formation and AGN activity.

Findings

Molecular gas masses range from 0.2 to 2.1×10^{10} M_0.

IR QSO properties are similar to local ULIRGs.

Star formation dominates IR emission, linked to AGN activity.

Abstract

We report CO detections in 17 out of 19 infrared ultraluminous QSO (IR QSO) hosts observed with the IRAM 30m telescope. The cold molecular gas reservoir in these objects is in a range of 0.2--2.1$\times 10^{10}M_\odot$ (adopting a CO-to-${\rm H_2}$ conversion factor $\alpha_{\rm CO}=0.8 M_\odot {\rm (K km s^{-1} pc^2)^{-1}}$). We find that the molecular gas properties of IR QSOs, such as the molecular gas mass, star formation efficiency ($L_{\rm FIR}/L^\prime_{\rm CO}$) and the 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$_{\rm FIR}$ and $L^\prime_{\rm CO(1-0)}$ 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 {\it 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 $\sim$ kpc scale and the central black hole accretion process on much smaller scales.