Aperture synthesis observations of the circumnuclear ring in the Galactic center

Abstract

The authors report 88 GHz aperture synthesis observations of HCN J = 1→0 emission and absorption in the central 5 pc of the Galaxy and single-dish measurements of HCN 1→0 and CO J = 7→6 line profiles at galactocentric radius R = 5.5 pc. The HCN synthesis data show a highly inclined, clumpy ring of molecular gas surrounding the ionized central 2 pc of the Galaxy. The ring is the inner edge of a thin disk extending in the HCN aperture synthesis data to about 5 pc and to ≥7 pc in lower excitation lines. The molecular gas is dynamically coupled to ionized gas in the central cavity. The dominant large-scale velocity pattern of the majority of the molecular gas in the inner 5 pc is rotation. No overall radial motion greater than about 20 - 30 km s<SUP>-1</SUP> is apparent. The neutral gas ring may represent a circumnuclear accretion disk which feeds interstellar matter into the central parsec.