THE GEOMETRY AND KINEMATICS OF THE BROAD-LINE REGION IN NGC-5548 FROM HST AND IUE OBSERVATIONS

The spatial and radial velocity distribution of broad-line-emitting gas in the Seyfert 1 galaxy NGC 5548 is examined through the process of reverberation mapping, which is done by detailed comparison of continuum and emission-line variations. Recent spectroscopic monitoring of NGC 5548 with HST and IUE allows us to resolve the ''transfer function'' (TF) that relates the continuum and emission-line variability. We also examine the radial velocity-resolved TFs, and confirm that predominantly radial motions of the line-emitting clouds can be excluded. We find that a broad-line region comprised of clouds that are orbiting a central source of mass similar to 10(8) M(circle dot) along randomly inclined Keplerian orbits and irradiated by a beamed continuum source yields a TF and line profile that are qualitatively consistent with the observations. In this model, the clouds that produce the variable C (IV) emission lie within 12 lt-days of the central source, and the continuum radiation is confined to a wide biconical beam (semi-opening angle 35 degrees-60 degrees) with the observer viewing into the cone.