TY - JOUR
T1 - A new look at the galactic circumnuclear disk
AU - Oka, Tomoharu
AU - Nagai, Makoto
AU - Kamegai, Kazuhisa
AU - Tanaka, Kunihiko
PY - 2011/5/10
Y1 - 2011/5/10
N2 - 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) × 105 M⊙ and a diameter of about 10pc, 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 HC 3N 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 ≃ 63K and H2 density of n(H2) ≃ 104.1cm-3. The bulk of the CND seems to have an overall, systematic infall motion, with a velocity of V infall ≃ 50kms-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 ≃ 2pc. It would trigger a burst of star formation, and subsequent processes could enhance the mass accretion rate to SgrA*.
AB - 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) × 105 M⊙ and a diameter of about 10pc, 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 HC 3N 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 ≃ 63K and H2 density of n(H2) ≃ 104.1cm-3. The bulk of the CND seems to have an overall, systematic infall motion, with a velocity of V infall ≃ 50kms-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 ≃ 2pc. It would trigger a burst of star formation, and subsequent processes could enhance the mass accretion rate to SgrA*.
KW - Galaxy: center
KW - ISM: kinematics and dynamics
KW - ISM: molecules
KW - galaxies: nuclei
KW - radio lines: ISM
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U2 - 10.1088/0004-637X/732/2/120
DO - 10.1088/0004-637X/732/2/120
M3 - Article
AN - SCOPUS:79955644448
VL - 732
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2
M1 - 120
ER -