We explore the formation of dusty gas walls induced by a circumnuclear starburst around an active galactic nucleus ( AGN ) .
We concentrate our attention on the role of the radiation force by a starburst as well as an AGN , where the effects of optical depth of dusty gas are taken into consideration .
First , we solve the hydrostatic equations in spherical symmetry coupled with the frequency-dependent radiative processes , to demonstrate that a geometrically thin , optically thick wall forms due to the radiation pressure by a circumnuclear starburst .
Next , in two-dimensional axisymmetric space , we analyze the configuration and the stability of geometrically thin walls which are in balance between radiation pressure and gravity .
As a result , it is shown that the radiation force by the circumnuclear starburst works to stabilize optically thick walls surrounding the nucleus .
In the case of a brighter starburst with a fainter AGN ( e.g . L _ { SB } / M _ { SB } \raisebox { 0.853583 pt } { \em$ > $ } \hskip { -9.389409 pt } % \raisebox { -5.121496 pt } { \em$ \sim $ } 10 [ L _ { \odot } / M _ { \odot } ] and L _ { AGN } \raisebox { 0.853583 pt } { \em$ < $ } \hskip { -9.389409 pt } \raisebox { -5.1214 % 96 pt } { \em$ \sim $ } 10 ^ { 11 } L _ { \odot } ) , there form double walls , an inner one of which is located between the nucleus and the circumnuclear starburst , and an outer one of which enshrouds both the starburst regions and the nucleus .
The total extinction of both walls turns out to be larger for a brighter starburst , which is A _ { V } \sim 10 for L _ { SB } / M _ { SB } \raisebox { 0.853583 pt } { \em$ > $ } \hskip { -9.389409 pt } % \raisebox { -5.121496 pt } { \em$ \sim $ } 10 ^ { 2 } [ L _ { \odot } / M _ { \odot } ] .
As a consequence , double walls could heavily obscure the nucleus to make the AGN type 2 .
The outer wall may provide an explanation for the recent indications for large-scale obscuring materials in Seyfert 2 ’ s .
Also , it is predicted that the AGN type is time-dependent according to the stellar evolution in the starburst , which shifts from type 2 to type 1 in several times 10 ^ { 7 } yr owing to the disappearance of walls .
In contrast , if the AGN itself is much brighter than the starburst as a quasar is , then neither wall forms regardless of the starburst activity and the nucleus is likely to be identified as type 1 .
To conclude , the radiatively-supported gas walls could be responsible for the putative correlation between AGN type and the starbursts , whereby Seyfert 2 galaxies are more frequently associated with circumnuclear starbursts than type 1 , whereas quasars are mostly observed as type 1 regardless of star-forming activity in the host galaxies .