Oral Presentation

Circumnuclear Molecular and Atomic Obscuring Structures in the Circinus Galaxy Revealed with ALMA

Author(s): Takuma Izumi (NAOJ); Keiichi Wada, Ryosuke Fukushige, Sota Hamamura (Kagoshima University); Kotaro Kohno (Tokyo University)

Presenter: Takuma Izumi (NAOJ)

We used the Atacama Large Millimeter/Submillimeter Array (ALMA) to map the CO(3-2) and [C I](1-0) lines, as well as their underlying continuum emission, from the central ~200 pc region of the Circinus galaxy that hosts the nearest type 2 Seyfert-class active galactic nucleus (AGN), with a spatial resolution of ~6-15 pc. The lines and continuum-emitting regions consist of a circumnuclear disk (CND; diameter ~70 pc) and spiral arms. The distribution of the continuum emission revealed a temperature-dependent dust geometry and possibly polar dust elongation in the torus region. The molecular mass of the CND is M(H2) ~3E6 Msun with a beam-averaged H2 column density of ~5E23 cm^-2 toward the AGN position, which contributes significantly to the nuclear obscuration. The [C I](1-0)/CO(3-2) ratio at the AGN position is unusually high, suggesting an X-ray dominated region-type chemistry. We decomposed the observed velocity fields into rotational and dispersion components, and revealed multi-phase dynamic nature in the r <~ 10 pc torus region, i.e., the diffuse atomic gas is more spatially extended along the vertical direction of the disk than the dense molecular gas. Through comparisons with our model predictions based on the radiation-driven fountain scheme, we indicate that atomic outflows are the driver of the geometrical thickness of that atomic disk. This supports the validity of the radiation-driven fountain scheme in the vicinity of this AGN, which would explain the long-lasting mystery, the physical origin of the AGN torus.