A NEW LOOK AT THE GALACTIC CIRCUMNUCLEAR DISK
- Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522 (Japan)
- Research Center for the Early Universe and Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
- Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan)
We report the results of millimeter and submillimeter molecular line mapping observations of the Galactic circumnuclear disk (CND). The CND appears as a large, asymmetric disk of warm molecular gas with a high CO J = 3-2/CO J = 1-0 intensity ratio exceeding 1.5. It has a mass of (2-5) x 10{sup 5} M{sub sun} and a diameter of about 10 pc, including a well-known 2-pc radius ring of dense molecular gas around the minispiral. The CND can be clearly traced by the J = 1-0 lines of HCN, H{sup 13}CN, HCO{sup +}, and HNC, but it is barely traced by N{sub 2}H{sup +}, SiO, CCS, and HC{sub 3}N lines. These data confirm the entity of the CND, and the 2-pc ring is just a part of it. Line ratios suggest that the CND is chemically immature, having higher density and higher temperature than the ambient gas. A one-zone large-velocity-gradient analysis finds that molecular gas in the CND has a typical kinetic temperature of T{sub k} {approx_equal} 63 K and H{sub 2} density of n(H{sub 2}) {approx_equal} 10{sup 4.1} cm{sup -3}. The bulk of the CND seems to have an overall, systematic infall motion, with a velocity of V{sub infall} {approx_equal} 50 km s{sup -1}. Our results are consistent with the scenario that the CND has been formed by tidal capture and disruption of a giant molecular cloud (GMC). The progenitor GMC may have been formed recently inside the 120-pc ring, possibly by the encounter with the small inner bar of the Galaxy. Toomre's Q parameter indicates that the CND is gravitationally stable now, but it will become unstable and fragment as gas accumulates at r {approx_equal} 2 pc. It would trigger a burst of star formation, and subsequent processes could enhance the mass accretion rate to Sgr A*.
- OSTI ID:
- 21576837
- Journal Information:
- Astrophysical Journal, Vol. 732, Issue 2; Other Information: DOI: 10.1088/0004-637X/732/2/120; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
CARBON MONOXIDE
GALAXIES
HYDROCYANIC ACID
HYDROGEN
NITRILES
SILICON OXIDES
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
ELEMENTS
HYDROGEN COMPOUNDS
INORGANIC ACIDS
INORGANIC COMPOUNDS
NONMETALS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
SILICON COMPOUNDS