The size of the broad-line region in the Seyfert galaxy NGC 4151

Abstract

Cross-correlation analysis of broad emission-line and optical continuum fluxes obtained from new spectrophotometric observations of NGC 4151 is used to estimate the size of the broad-line region (BLR) in this galaxy. The size of the BLR is found to be ~6 lt-days, though this may easily be in error by a factor of 2. While the uncertainty is rather large, it is emphasized that this is a considerable improvement over previous determinations in which the magnitude of the uncertainties was not fully appreciated. It is also pointed out that there is insufficient evidence to support earlier claims that the different BLR radii inferred from cross-correlation of different broad lines with the continuum provide evidence for ionization stratification within the BLR.