Resolving the Interstellar Medium in Ultraluminous Infrared QSO Hosts with ALMA

TL;DR

This study uses ALMA to resolve molecular gas in eight ultraluminous IR QSOs, revealing diverse morphologies, kinematics, and a correlation between black hole accretion and star formation, shedding light on galaxy evolution.

Contribution

First detailed ALMA observations of CO and continuum in IR QSO hosts, revealing gas morphology, kinematics, and the link between AGN activity and star formation.

Findings

Resolved CO emission shows diverse morphologies.

Detected a correlation between black hole accretion rate and star formation.

Identified different gas kinematic categories, including rotating disks and mergers.

Abstract

We present ALMA observations of the CO(1-0) line and 3-mm continuum emission in eight ultraluminous infrared (IR) quasi-stellar objects (QSOs) at z = 0.06-0.19. All eight IR QSO hosts are clearly resolved in their CO molecular gas emission with a median source size of 3.2 kpc, and seven out of eight sources are detected in 3-mm continuum, which is found to be more centrally concentrated with respect to molecular gas with sizes of 0.4-1.0 kpc. Our observations reveal a diversity of CO morphology and kinematics for the IR QSO systems which can be roughly classified into three categories, rotating gas disk with ordered velocity gradient, compact CO peak with disturbed velocity, and multiple CO distinct sources undergoing a merger between luminous QSO and a companion galaxy separated by a few kpc. The molecular gas in three of IR QSO hosts are found to be rotation-dominated with the ratio of the maximum rotation velocity to the local velocity dispersion of $V_{\rm rot}/\sigma=4-6$. Basic estimates of the dynamical masses within the CO-emitting regions give masses between $7.4\times10^9$ and $6.9\times10^{10}$ $M_\odot$. We find an increasing trend between BH mass accretion rate and star formation rate (SFR) over three orders of magnitude in far-IR luminosity/SFR, in line with the correlation between QSO bolometric luminosity and SF activity, indicative of a likely direct connection between AGN and SF activity over galaxy evolution timescales.