Line variations in quasars and Seyfert galaxies

TLDR: In this paper, the size of broad-line regions in three well-studied Seyfert I galaxies are presented, and differences between these and previously reported size estimates for NGC 4151 are discussed.

Abstract: Quantitative estimates of the sizes of broad-line regions in three well-studied Seyfert I galaxies are presented, and differences between these and previously reported size estimates for NGC 4151 are discussed. Both Lick Observatory and IUE satellite data on NGC 4151 are analyzed, and it is shown that both are consistent with the high-ionization filaments (those emitting C IV, He II, and the high-order Balmer lines) mostly lying about 5 lt-day from the central source. The low-ionization filaments are 3 or 4 times further out. The Ohio State data on Akn 120 show the H-beta emitting region to be about 6 lt-day from the central source, and IUE data suggest that the Ly-alpha region in Mrk 509 is about 10 lt-day out. The present results imply that the densities in broad-line regions are a couple of orders of magnitude higher than in current standard models. For the objects studied here, the light crossing times are of the same order of magnitude as the continuum variability time scales, so kinematic mapping of the broad-line regions will be extremely difficult. 56 references.