On the Disappearance of a Cold Molecular Torus around the Low-luminosity Active Galactic Nucleus of NGC 1097
Journal article, 2017
We used the Atacama Large Millimeter/Submillimeter Array to map the CO(3-2) and the underlying continuum emissions around the type-1low-luminosity active galactic nucleus (LLAGN; bolometric luminosity less than or similar to 10(42) erg. s(-1)) of NGC 1097 at similar to 10 pc resolution. These observations revealed a detailed cold gas distribution within a similar to 100 pc of this LLAGN. In contrast to the luminous Seyfert galaxy NGC 1068, where a similar to 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 greater than or similar to 2-3 less than that found for NGC 1068 by using the same CO-to-H-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 mu m H-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.
galaxies: active
galaxies: Seyfert
galaxies: individual (NGC 1097)
galaxies: ISM
Author
T. Izumi
National Astronomical Observatory of Japan
K. Kohno
Research Center for the Early Universe
University of Tokyo
K. Fathi
Valhallav. 67
E. Hatziminaoglou
European Southern Observatory (ESO)
R. I. Davies
Max Planck Society
S. Martin
European Southern Observatory Santiago
Atacama Large Millimeter-submillimeter Array (ALMA)
S. Matsushita
Academia Sinica
E. Schinnerer
Max Planck Society
D. Espada
National Astronomical Observatory of Japan
The Graduate University for Advanced Studies (SOKENDAI)
Susanne Aalto
Chalmers, Earth and Space Sciences, Onsala Space Observatory
K. Onishi
Ehime University
J. L. Turner
University of California
M. Imanishi
National Astronomical Observatory of Japan
The Graduate University for Advanced Studies (SOKENDAI)
K. Nakanishi
The Graduate University for Advanced Studies (SOKENDAI)
National Astronomical Observatory of Japan
D. S. Meier
New Mexico Institute of Mining and Technology
K. Wada
Kagoshima University
N. Kawakatu
National Institute of Technology (KOSEN)
T. Nakajima
Nagoya University
Astrophysical Journal Letters
2041-8205 (ISSN) 2041-8213 (eISSN)
Vol. 845 1 L5- L5Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
Infrastructure
Onsala Space Observatory
DOI
10.3847/2041-8213/aa808f