Lack of Correlations between Cold Molecular Gas and AGN Properties in Type 1 AGNs at $z \lesssim 0.5$

TL;DR

This study investigates the relationship between cold molecular gas and active galactic nucleus (AGN) properties in local type 1 AGNs, finding no strong correlation and suggesting other factors influence AGN activity.

Contribution

It provides new CO(2--1) observations of bright quasars and combines them with literature data to analyze molecular gas and AGN properties in a large sample.

Findings

CO luminosity does not correlate with AGN luminosity or Eddington ratio.

Type 1 AGNs split into two groups based on infrared-to-CO luminosity ratio.

No evidence that AGN feedback rapidly quenches star formation.

Abstract

We present new NOrthern Extended Millimeter Array (NOEMA) observations of the CO(2--1) emission in eight of the brightest Palomar-Green quasars at $z \lesssim 0.5$ to investigate the role of active galactic nuclei (AGN) feedback in luminous quasars detected at low redshifts. We detect CO(2--1) emission in three objects, from which we derive CO luminosities, molecular gas masses and fractions, and gas depletion times. In combination with data available in the literature, we build a total sample of 138 local type 1 AGNs with CO(2--1) measurements. We compare the AGN properties with the host galaxy molecular gas properties, considering the systems non-detected in CO emission. We find that the CO luminosity does not correlate with AGN luminosity and Eddington ratio, while the molecular gas fraction is weakly correlated with Eddington ratio. The type 1 AGNs can be roughly separated into two populations in terms of infrared-to-CO luminosity ratio, one population presenting values typically found in normal star-forming systems, while the other have lower ratio values, comparable to those measured for starbursts. We find no evidence that AGN feedback rapidly quenches star formation in type 1 AGNs. Our results may imply an underlying the role of host galaxy gravitational instabilities or the fast inflow of cold gas in triggering AGN activity.