Abstract

The central engine of a quasar is thought to be a black hole surrounded by an accretion disk which radiates as a continuum source. This radiation photoionises nearby gas clouds which comprise the broad line region (BLR). The dynamics of the broad line region are modelled, taking account of the axial symmetry of the quasar. The model investigates the effects of an optically thick accretion disk in the centre. The role of a torus of dust encircling the broad line region in the plane of the accretion disk is also considered. The predicted emission line shapes are compared to observed spectra, looking in particular at the asymmetry and redshift offset of the emission lines. It was found that an outflow model with a large dusty torus (similar to the current unified model of Seyfert galaxies) was able to produce asymmetries consistent with the observations. Other outflow models, with thinner opaque disks, could not reproduce the observed asymmetries. It was also established that the BLR clouds could not be in Keplerian orbits as this produced unrealistic emission line profiles.

The internal structure of a quasar is believed to consist of the elements shown in the diagram.

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