We investigate the properties of the ionized gas irradiated by an active galactic nucleus ( AGN ) based on our “ radiation-driven fountain ” model for the nearest type-2 Seyfert galaxy , the Circinus galaxy \citep wada2016 .
We conducted “ quasi-three dimensional ” spectral analysis using the spectral synthesis code C LOUDY and obtained the surface brightness distributions of lines , such as H \alpha , H \beta , [ O III ] , [ N II ] , and [ S II ] for the central 16-parsec region .
The ionized regions observed based on these lines show a conical morphology around the rotation axis , even if we do not phenomenologically postulate the presence of an optically thick “ torus ” .
This region also shows non-uniform internal structures , reflecting the inhomogeneous structure of fountain flows .
Using ionization diagnostic diagrams , we investigated the spectral properties of the ionized gas .
The diagrams based on the line ratios of [ N II ] /H \alpha and [ S II ] /H \alpha show that most regions of the cone have the same properties as those in the narrow line regions ( NLRs ) in AGNs , whereas using [ O I ] /H \alpha , the central 10-pc regions are rather LINER-like .
The gas density , temperature , and ionizing parameter in regions identified as “ NLR ” are typically n \sim 300 - 1500 cm ^ { -3 } , T \sim 1 - 3 \times 10 ^ { 4 } K , and U \sim 0.01 , respectively .
The morphology and [ O III ] intensity are similar to the base of the observed [ O III ] cone in the Circinus galaxy , implying some physical connections with the origin of the \sim 100 parsec scale NLR .