1999ApJ...518L...9S

As a consequence of the improved signal-to-noise ratio, spectral resolution, and wavelength coverage, various authors have introduced, without strong justification, new emitting regions to account for various emission-line profile differences in active galactic nuclei. The so-called C IV λ1549 intermediate-line region (ILR) appears to be especially ill-defined. We present observational evidence that suggests the ILR is statistically indistinguishable from the classical narrow-line region (NLR). We present the results of theoretical models showing that a smooth density gradient in the NLR can produce C IV and Balmer emission lines with different widths. The putative ILR component has often been included with the broad line profile in studies of C IV broad-line region (BLR) properties. Failure to account for the composite nature of C IV emission, and for the presence of sometimes appreciable NLR C IV emission, has important consequences for our understanding of the BLR.