ALMA observations of molecular tori around massive black holes
Journal article, 2019

We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO(3-2) emission in a sample of seven Seyfert/LINER galaxies at the unprecedented spatial resolution of 0 .″ 1 = 4-8 pc. Our aim is to explore the close environment of active galactic nuclei (AGN), and the dynamical structures leading to their fueling, through the morphology and kinematics of the gas inside the sphere of influence of the black hole. The selected galaxies host low-luminosity AGN and have a wide range of activity types (Seyferts 1 to 2, LINERs), and barred or ringed morphologies. The observed maps reveal the existence of circumnuclear disk structures, defined by their morphology and decoupled kinematics, in most of the sample. We call these structures molecular tori, even though they often appear as disks without holes in the center. They have varying orientations along the line of sight, unaligned with the host galaxy orientation. The radius of the tori ranges from 6 to 27 pc, and their mass from 0.7 × 10 7 to 3.9 × 10 7 M · . The most edge-on orientations of the torus correspond to obscured Seyferts. In only one case (NGC 1365), the AGN is centered on the central gas hole of the torus. On a larger scale, the gas is always piled up in a few resonant rings 100 pc in scale that play the role of a reservoir to fuel the nucleus. In some cases, a trailing spiral is observed inside the ring, providing evidence for feeding processes. More frequently, the torus and the AGN are slightly off-centered with respect to the bar-resonant ring position, implying that the black hole is wandering by a few 10 pc amplitude around the center of mass of the galaxy. Our spatial resolution allows us to measure gas velocities inside the sphere of influence of the central black holes. By fitting the observations with different simulated cubes, varying the torus inclination and the black hole mass, it is possible to estimate the mass of the central black hole, which is in general difficult for such late-type galaxies, with only a pseudo-bulge. In some cases, AGN feedback is revealed through a molecular outflow, which will be studied in detail in a subsequent article.

Galaxies: ISM

Galaxies: nuclei

Galaxies: active

Galaxies: spiral

Galaxies: kinematics and dynamics


F. Combes

LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres

Collège de France

S. G. Burillo

Spanish National Observatory (OAN)

A. Audibert

LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres

L. K. Hunt

Arcetri Astrophysical Observatory

A. Eckart

University of Cologne

Susanne Aalto

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

V. Casasola

Arcetri Astrophysical Observatory

Istituto di Radioastronomia

F. Boone

Centre national de la recherche scientifique (CNRS)

M. Krips

Domaine universitaire de Grenoble

Serena Viti

University College London (UCL)

K. Sakamoto

Academia Sinica

Sebastien Muller

Chalmers, Space, Earth and Environment, Onsala Space Observatory, Observation Support

K. M. Dasyra

University of Athens

National Observatory of Athens

P. van der Werf

Leiden University

S. Martin

European Southern Observatory Santiago

Atacama Large Millimeter-submillimeter Array (ALMA)

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 623 A79

Subject Categories

Astronomy, Astrophysics and Cosmology



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