アブストラクト：
The “torus” of active galactic nuclei (AGNs) is a widely accepted idea to explain the existence or absence of an AGN’s broad line. However, its physical nature has been poorly understood. Here, we conducted <~10 pc scale (i) molecular CO and (ii) atomic CI observations toward the nearest AGN, the Circinus, with ALMA. We revealed that the cold gas provides sufficient nuclear obscuration. The molecular disk shows a puffed-up structure at the close vicinity of the AGN, whereas it is geometrically thin at r > 20 pc. Meanwhile, the diffuse atomic disk shows a larger scale height than the dense molecular disk, manifesting the multi-phase geometry. These findings are consistent with our recent hydrodynamical + chemical simulation that attributes the origin of the torus-thickness to the “(AGN’s) radiation-driven fountain”, which generates strong turbulence inside the disk.