On the Disappearance of a Cold Molecular Torus around the Low-luminosity Active Galactic Nucleus of NGC 1097
- National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
- Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan)
- Valhallav. 67, SE-114 28 Stockholm (Sweden)
- European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München (Germany)
- Max-Planck-Institute für Extraterrestrische Physik, Postfach 1312, D-85741 Garching (Germany)
- Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago 763-0355 (Chile)
- Academia Sinica, Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan (China)
- Max Planck Institute for Astronomy, Königstuhl 17, Heidelberg D-69117 (Germany)
- Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Observatory, SE-439 92 Onsala (Sweden)
- Research Center for Space and Cosmic Evolution, Ehime University, 2-5 Bunkyocho, Matsuyama, Ehime 790-0826 (Japan)
- Department of Physics and Astronomy, UCLA, 430 Portola Plaza, Los Angeles, CA 90095-1547 (United States)
- Department of Physics, New Mexico Institute of Mining and Technology, 801 Leroy Place, Soccoro, NM 87801 (United States)
- Kagoshima University, Kagoshima 890-0065 (Japan)
- Faculty of Natural Sciences, National Institute of Technology, Kure College, 2-2-11 Agaminami, Kure, Hiroshima 737-8506 (Japan)
We used the Atacama Large Millimeter/Submillimeter Array to map the CO(3–2) and the underlying continuum emissions around the type-1 low-luminosity active galactic nucleus (LLAGN; bolometric luminosity ≲10{sup 42} erg s{sup −1}) of NGC 1097 at ∼10 pc resolution. These observations revealed a detailed cold gas distribution within a ∼100 pc of this LLAGN. In contrast to the luminous Seyfert galaxy NGC 1068, where a ∼7 pc cold molecular torus was recently revealed, a distinctively dense and compact torus is missing in our CO(3–2) integrated intensity map of NGC 1097. Based on the CO(3–2) flux, the gas mass of the torus of NGC 1097 would be a factor of ≳2–3 less than that found for NGC 1068 by using the same CO-to-H{sub 2} conversion factor, which implies less active nuclear star formation and/or inflows in NGC 1097. Our dynamical modeling of the CO(3–2) velocity field implies that the cold molecular gas is concentrated in a thin layer as compared to the hot gas traced by the 2.12 μm H{sub 2} emission in and around the torus. Furthermore, we suggest that NGC 1097 hosts a geometrically thinner torus than NGC 1068. Although the physical origin of the torus thickness remains unclear, our observations support a theoretical prediction that geometrically thick tori with high opacity will become deficient as AGNs evolve from luminous Seyferts to LLAGNs.
- OSTI ID:
- 22872568
- Journal Information:
- Astrophysical Journal Letters, Vol. 845, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United Kingdom
- Language:
- English
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