Molecular gas excitation and outflow properties of obscured quasars at z  ∼   0.1

¹ Instituto de Astrofísica de Canarias, Calle Vía Láctea, s/n, E-38205 La Laguna, Tenerife, Spain
² Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
³ Observatorio Astronómico Nacional (OAN-IGN)-Observatorio de Madrid, Alfonso XII, 3, 28014 Madrid, Spain
⁴ Instituto de Física Fundamental, CSIC, Calle Serrano 123, 28006 Madrid, Spain
⁵ Dipartimento di Fisica e Astronomia, Università di Firenze, Via G. Sansone 1, 50019 Sesto F.no (Firenze), Italy
⁶ INAF – Osservatorio Astrofisico di Arcetri, largo E. Fermi 5, 50127 Firenze, Italy
⁷ INAF Istituto di Astrofisica e Planetologia Spaziali, Roma, Italy

^⋆ Corresponding author: anelise.audibert@iac.es

Received: 4 December 2024
Accepted: 5 May 2025

Abstract

To investigate the impact of winds and jets with a low to moderate power on the cold molecular gas reservoirs of active galactic nuclei (AGN), we present observations with a high angular resolution with ALMA CO(2–1) and CO(3–2) of a sample of six type 2 quasars (QSO2s) at z ∼ 0.1 from the quasar feedback (QSOFEED) sample. We used spatially resolved molecular line ratio maps, defined as R₃₂ ≡ L′_{CO(3 − 2)}/L′_{CO(2 − 1)}, and kinematic modeling to constrain the changes in the gas excitation and to identify gas outflows, respectively. The molecular outflows are co-spatial with regions with R₃₂ > 1, indicating a higher temperature than in the disks and the presence of optically thin gas in the outflows. Considering more and less conservative scenarios to measure the outflow properties, we find mass outflow rates of 5 ≲ Ṁ ≲ 150 M_⊙ yr⁻¹, which is much lower than those expected from their AGN luminosities of ∼10^{45.5 − 46} erg s⁻¹, based on scaling relations from the literature. The outflow kinetic energies might be driven by the combined action of jets and radiation pressure winds, and the radiative coupling efficiencies (ϵ_AGN ≡ Ė_out/L_bol) range from 10⁻⁶ < ϵ_AGN < 10⁻⁴ and the jet coupling efficiencies (ϵ_jet ≡ Ė_out/P_jet) from 10⁻³ < ϵ_AGN < 10⁻². A linear regression including the six QSO2s follows the locus of ϵ_jet ∼ 0.1%, although we found no strong correlation because of the small-number statistics. Our results provide further evidence that AGN-driven jets/winds disturb the molecular gas kinematics and excitation within the central several kiloparsec of the galaxies. The coupling between compact jets and the interstellar medium might be relevant to AGN feedback, even in the case of radio-quiet galaxies, which are more representative of the AGN population. Finally, the warm (H₂) and cold (CO) molecular gas phases seem to be tracing the same outflow. The main distinction between them is the mass they carry, while the warm ionized outflows ([OIII]) do not seem to be another face of the same outflow, as their orientation, velocity, and radius are different.