# Integral field spectroscopy of nearby QSOs II. The molecular gas content and condition for star formation

## TL;DR

This study investigates the molecular gas content in nearby QSOs using CO observations and optical spectroscopy, revealing differences based on host galaxy morphology and implications for star formation and black hole activity.

## Contribution

It provides new insights into the molecular gas properties of low-redshift QSOs and their relation to star formation and black hole accretion, highlighting differences between disc- and bulge-dominated hosts.

## Key findings

- Gas-rich mergers show starburst signatures.
- Disc-dominated QSOs have gas fractions similar to normal star-forming galaxies.
- Bulge-dominated QSOs have lower gas fractions but higher star formation efficiencies.

## Abstract

We present single-dish CO(1-0) and CO(2-1) observations for 14 low-redshift quasi-stellar objects (QSOs). In combination with optical integral field spectroscopy we study how the cold gas content relates to the star formation rate (SFR) and black hole accretion rate. CO(1-0) is detected in 8 of 14 targets and CO(2-1) is detected in 7 out of 11 cases. The majority of disc-dominated QSOs reveal gas fractions and depletion times well matching normal star forming systems. Two gas-rich major mergers show clear starburst signatures with higher than average gas fractions and shorter depletion times. Bulge-dominated QSO hosts are mainly undetected in CO(1-0) which corresponds, on average, to lower gas fractions than in disc-dominated counterparts. Their SFRs however imply shorter than average depletion times and higher star formation efficiencies. Negative QSO feedback through removal of cold gas seems to play a negligible role in our sample. We find a trend between black hole accretion rate and total molecular gas content for disc-dominated QSOs when combined with literature samples. We interpret this as an upper envelope for nuclear activity which is well represented by a scaling relation between the total and circum-nuclear gas reservoir accessible for accretion. Bulge-dominated QSOs significantly differ from that scaling relation and appear uncorrelated with the total molecular gas content. This could be explained either by a more compact gas reservoir, blow out of the gas envelope through outflows, or a different ISM phase composition.