The role of an extended corona in the formation of emission lines and continuum in active galactic nuclei

We study a model of an accretion disc surrounded by an extended corona of the temperature 10 7 10 8 K. This corona modifies the disk spectrum since it redirects a significant fraction of the emission from the central parts towards the more distant parts of the disk. The same corona is indirectly the source of the broad emission lines because we expect the formation of cool clouds at the basis of the corona due to thermal instabilities. We model the number of the clouds and their motion through the corona adopting a few different physically sound assumptions. Comparing the predicted optical/UV continua and emission line ratios and profiles with the observed values we favor a particular model of a typical quasar. It radiates at � 0.5 of the Eddington luminosity, the corona surrounding the disk is additionally heated in excess of the Inverse Compton heating, and the broad line clouds are most probably destroyed when accelerated vertically above the sound speed within the corona.