A New Look at the Galactic Circumnuclear Disk

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 105 M and a...

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Bibliographic Details
Published in:The Astrophysical journal 2011-05, Vol.732 (2), p.120-jQuery1323908884598='48'
Main Authors: Oka, Tomoharu, Nagai, Makoto, Kamegai, Kazuhisa, Tanaka, Kunihiko
Format: Article
Language:English
Subjects:
Astronomy
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Asymmetry
Bursting
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
Density
Disks
Earth, ocean, space
ELEMENTS
Exact sciences and technology
GALAXIES
HYDROCYANIC ACID
HYDROGEN
HYDROGEN COMPOUNDS
INORGANIC ACIDS
INORGANIC COMPOUNDS
NITRILES
NONMETALS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
Progenitors (astrophysics)
SILICON COMPOUNDS
SILICON OXIDES
Star formation
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Summary: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 105 M 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, H13CN, HCO+, and HNC, but it is barely traced by N2H+, SiO, CCS, and HC3N 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 k 63 K and H2 density of n(H2) 104.1 cm--3. The bulk of the CND seems to have an overall, systematic infall motion, with a velocity of V infall 50 km s--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 2 pc. It would trigger a burst of star formation, and subsequent processes could enhance the mass accretion rate to Sgr A*.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/732/2/120