Discovery of a Nuclear Gas Bar Feeding the Active Nucleus in Circinus

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Abstract
We report the discovery of gas inflow motions toward the active nucleus of the Circinus galaxy caused by the nonaxisymmetric potential of a nuclear gas bar. Evidence for dust associated with the bar comes from the HST/NICMOS H-K color map, whereas the streaming motions along the gas bar are seen in the velocity field of the H2 S(1) (1-0) emission line. The gas bar is about 100 pc long with a visual extinction in excess of 10 mag. Indication for the gaseous nature of this bar comes from the lack of a stellar counterpart even in the K band, where the extinction is greatly reduced. We also use the NICMOS emission-line images (Paα, [Si VI], and [Fe II]) to study the innermost region of the ionization cones and the nuclear star-forming activity. We discuss the possible relationship of these components with the gaseous bar.
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