Oral Presentation
Radiative transfer calculations for dense molecular gas based on the radiation-driven fountain model
Presenter: Shunsuke Baba (鹿児島大学)
It is widely accepted that active galactic nuclei are surrounded by an optically and geometrically thick dusty toroidal structure (AGN torus) and that the line of sight direction relative to the torus axis makes the difference in whether broad emission lines are observed. As a formation mechanism of the torus, our group proposed the radiation-driven fountain model, where the radiation from an accretion disk drives unsteady outflows, part of which become failed winds falling to the equatorial plane, forming a quasi-steady torus. We have been verifying the model by comparing the predictions from simulations with high-resolution observations of one of the nearest AGNs, the Circinus galaxy. Recently, the galaxy’s nucleus was found to show an inverse P-Cygni profile in the HCN J=3-2 line, intimating a molecular inflow. To compare this result with our model, we performed radiative transfer calculations for similar dense gas tracer HCO+ and investigated in what conditions such profiles are reproduced. We found that the HCO+ J=3-2 line can be detected in absorption when the inclination angle is larger than 85 deg, being consistent with that estimated from observations. The line shows inverse P-Cygni profiles at some azimuthal angles, however, it also shows normal P-Cygni profiles (outflows) at some other azimuthal angles. This result suggests that the detection of an inverse P-Cygni profile could be an occasional phenomenon.
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