The Structure of the Torus and Broad-line Region Of AGNs

Details The Structure of the Torus and Broad-line Region Of AGNs The Structure of the Torus and Broad-line Region Of AGNs

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...21111802g&link_type=abstract

American Astronomical Society, AAS Meeting #211, #118.02; Bulletin of the American Astronomical Society, Vol. 39, p.947

Astronomy and Astrophysics

Astronomy

1

Scientific paper

Reverberation mapping shows that there is substantial radial stratification of the broad-line regions of AGNs. This stratification exceeds what is predicted by the standard "locally optimized cloud” (LOC) model of Baldwin et al. where the integrated line spectrum arises from a distribution of clouds each seeing a similar ionizing spectrum but with a range of densities and distances from the source. We argue that a high covering factor for the BLR (≈ 40% for NGC 5548) is inescapable and that such a high covering factor coupled with the lack of Lyman-edge absorption from the BLR requires a flattened distribution of BLR gas viewed through a hole near the pole. A necessary consequence of this geometry is that the BLR completely covers the central source when viewed from near the equatorial plane. This means that the radiation seen by the outer BLR and dusty torus is heavily absorbed by the inner BLR. We have quantitatively modeled this and show that in the case of NGC 5548 our self-shielding model produces BLR stratification in agreement with reverberation mapping. The BLR obscuration also removes the problem of the torus covering factor being greater than the BLR covering factor, and gives consistency with the observed fraction of obscured AGNs. In addition to this the flux reduction at the torus reduces the problem of AGN dust-reverberation lags giving radii smaller than the dust-sublimation radii. This research has been supported by the Space Telescope Science Institute through grant AR-09926.01, and by the National Science Foundation through grant AST 03-07912.

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