Decoding the molecular torus of NGC 1068

Astronomy and Astrophysics, vol. 699, pp. A187

Abstract

Context. Previous kinematic analysis of the pc-scale molecular torus in NGC 1068 have revealed a very complex and inhomogeneous system involving several physical components, such as non-circular motions, turbulence, high-velocity outflows, and possibly even counter-rotation. Aims. Our study aims to dissect the kinematics and morphology of the molecular gas within the near-nuclear region of NGC 1068 to understand the mechanisms in the central Active Galactic Nucleus (AGN) that might fuel it, and the impact of its energy output on the surrounding molecular gas. Methods. We present high angular and spectral resolution ALMA observations of the HCO+ (J = 4→3) and CO (J = 3→2) molecular lines in the near-nuclear region of the prototype Seyfert 2 galaxy NGC 1068. The spatial resolution (1.1 pc) is almost two times better than that of previous studies examining the same molecular lines at the same transitions and is the highest resolution achievable with ALMA at these frequencies. Our analysis focuses on moment maps, position-velocity (PV) diagrams, and spectra obtained at the position of the nuclear continuum source, along with a simple kinematic model developed using the 3DBarolo software. Results. Our observations reveal significant asymmetry between the eastern and western sides of the nuclear disc in terms of morphology, velocity, and line intensity. The broad lines (σ∼90 km/s) seen in the inner 2 pc could be accounted for by either beam smearing or highly turbulent gas in this region. Outside this radius, the mean velocities drop to ±30 km/s, which cannot be explained by asymmetric drift. We find low velocity connections extending to 13 pc, suggesting interactions with larger scale structures. The CO/HCO+ line ratio at the nucleus reported here are extremely low compared to values in the literature of the same galaxy at lower spatial resolutions. We find high-velocity redshifted clouds in absorption and emission at the nuclear position. Conclusions. The molecular environment near the nucleus of NGC 1068 is highly disturbed and asymmetric, marked by the presence of a high-velocity infalling cloud. High excitation temperatures, high molecular column densities, along with the unusually low CO/HCO+ line ratio close to the nucleus seem to indicate intense interaction with AGN radiation. These findings underscore the complexity of AGN feeding mechanisms and the pivotal role of high-resolution studies in unravelling the physical processes at play near supermassive black holes.

Authors 16

1. V. Gámez Rosas Aachen Leiden Observatory

   Leiden University · University of Liège · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

   STAR Institute, Institut d'Astrophysique et de Géophysique, University of Liège, Allée du 6 août, 19C, B-4000 Liège, Belgium

2. Paul P. van der Werf Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

3. J. F. Gallimore

   Bucknell University

   Affiliation as printed

   Department of Physics and Astronomy, Bucknell University, One Dent Drive Lewisburg, PA 17837, USA

4. C. M. Violette Impellizzeri Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

5. Wayne Jaffe Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

6. S. García‐Burillo

   Spanish National Observatory

   Affiliation as printed

   Observatorio Astronómico Nacional, Aptdo 1143, 28800 Alcalá de Henares, Spain

7. S. Aalto

   Chalmers University of Technology

   Affiliation as printed

   Chalmers University of Technology, Department of Earth and Space Sciences, Onsala Space Observatory, 439 92 Onsala, Sweden

8. L. Burtscher Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

9. V. Casasola

   Istituto di Radioastronomia di Bologna

   Affiliation as printed

   INAF Istituto di Radioastronomia, Via Piero Gobetti 101, 40129 Bologna, Italy

10. Françoise Combes

    Centre National de la Recherche Scientifique · Collège de France · Observatoire de Paris · Sorbonne Université · Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères

    Affiliation as printed

    Observatoire de Paris, LERMA, Collège de France, CNRS, PSL University, Sorbonne University, 75014 Paris, France

11. C. Henkel

    Max Planck Institute for Radio Astronomy

    Affiliation as printed

    MPI für Radioastronomie Auf dem Hügel 69, 53121 Bonn, Germany

12. Isabel Márquez

    Instituto de Astrofísica de Andalucía

    Affiliation as printed

    Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain

13. S. Martín

    Atacama Large Millimeter Submillimeter Array · European Southern Observatory

    Affiliation as printed

    European Southern Observatory, Alonso de Córdova, 3107, Vitacura, Santiago 763-0355, Chile

    Joint ALMA Observatory, Alonso de Córdova, 3107, Vitacura, Santiago 763-0355, Chile

14. Cristina Ramos Almeida

    Universidad de La Laguna · Instituto de Astrofísica de Canarias

    Affiliation as printed

    Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain

    Instituto de Astrofísica de Canarias Calle Vía Láctea, s/n E-38205 La Laguna, Tenerife, Spain

15. S. Viti Aachen Leiden Observatory

    Leiden University · Leiden Observatory

    Affiliation as printed

    Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

16. Asunción Fuente

    Centro de Astrobiología

    Affiliation as printed

    Centro de Astrobiología (CAB), CSIC-INTA, Ctra. de Ajalvir, km 4, Torrejón de Ardoz, 28850 Madrid, Spain