RESPONSE FUNCTIONS AS DIAGNOSTICS OF THE BROAD-LINE REGION IN ACTIVE GALACTIC NUCLEI .2. ANISOTROPIC LINE EMISSION

The effect of anisotropic line emission on the form of the response function for a wide range of broad-line region (BLR) models is discussed. Anisotropy can dramatically alter the form of the response function, and must therefore be taken into account when comparing observations with theoretical BLR structures. We calculate radial anisotropy distributions, and hence anisotropic response functions, for many of the strong broad emission lines seen in active galactic nuclei (AGN) spectra for a set of spherical pressure-law BLR models. The majority of lines are emitted anisotropically at some radii in all the models, particularly when the ionization parameter is large. The pressure-law model anisotropic response functions are compared with those recovered from intensive optical/UV monitoring campaigns for the Seyfert 1 galaxy NGC 5548. We show that the high-ionization lines in this AGN probably arise from a spherical BLR component comprising clouds with moderate column densities. These clouds are optically thin at the Lyman limit in the inner BLR. Most of the low-ionization line emission arises from a non-spherical BLR component.