Kinematics of the Broad Emission Line Region in NGC 5548

Abstract

We derive both total flux and velocity-resolved response functions for the CIV 1549 emission line from the data obtained in the 1993 NGC 5548 monitoring campaign. These response functions imply: 1.) the emission region stretches from inside 1 lt-d to outside 10 lt-d, and is probably better described as round than flat; 2.) the velocity field is dominated by a red/blue symmetric component (e.g. 2--d or 3--d random motions, or rotation in a disk) but there is also {\it significant} radial infall. Quantitative modelling indicates that the random speeds are typically a few times as large as the radial speed. However, no simple model gives a completely acceptable fit to the data. These inferences rule out numerous simple and otherwise plausible models for broad line region dynamics, including outflowing winds, radial free-fall, rotation in a disk, or collisionless orbital motion.