Gas and Dust Emission from the Nuclear Region of the Circinus Galaxy

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Abstract
Simultaneous modeling of the line and continuum emission from the nuclear region of the Circinus galaxy is presented. Composite models that include the combined effect of shocks and photoionization from the active center and from the circumnuclear star-forming region are considered. The effects of dust reradiation, bremsstrahlung from the gas, and synchrotron radiation are treated consistently. Models that fit the continuum energy distribution of Circinus are used to constrain all possible models suitable for the line emission; they are all, together, aimed to converge to a most probable representation of the central emission region of Circinus. The proposed model accounts for two important observational features. First, the high obscuration of Circinus central source is produced by high-velocity and dense clouds with characteristic dust-to-gas ratios above 10-12. Their large velocities, up to 1500 km s-1, place them very close to the active center. Second, the derived size of the line-emitting region (~13 pc) is well in agreement with the observed limits for the coronal (<10 pc) and narrow-line regions (~30 pc) of Circinus.
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