Emission-line variations and broad-line region kinematics of NGC 5548

Abstract

Sixteen spectroscopic observations of the Seyfert galaxy NGC 5548 were made between 1979 March and 1984 June at Palomar and Steward Observatories. We have measured broad-line flux variations correlated with nonstellar continuum changes. Hβ, Hγ, and He II λ4686 all respond rapidly to continuum variations providing strong evidence for photoionization by a central continuum source. Additionally, Hβ profile variations have occurred during our 1900 day monitoring period. These profile variations also correlate with changes in the continuum, but lag behind by ~90 days or less. We have proposed a kinematic model that incorporates radial outflow and an internal line opacity source to explain qualitatively the observed Hβ profile variations. This model can also account naturally for the lag between profile and continuum variations as a light travel time effect. Other types of motion, including purely chaotic or rotational, cannot account for the observed changes.