A new look at the galactic circumnuclear disk

Tomoharu Oka, Makoto Nagai, Kazuhisa Kamegai, Kunihiko Tanaka

Research output: Contribution to journalArticle

41 Citations (Scopus)

Abstract

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*.

Original languageEnglish
Article number120
JournalAstrophysical Journal
Volume732
Issue number2
DOIs
Publication statusPublished - 2011 May 10

Keywords

  • Galaxy: center
  • ISM: kinematics and dynamics
  • ISM: molecules
  • galaxies: nuclei
  • radio lines: ISM

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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