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Our recent statistical investigations of the broad UV lines of luminous QSOs (Steidel \& Sargent's absorption line surveys and the LBQS) indicate that the traditional broad line region (BLR) consists of at least two kinematically distinct regions -- one producing line emission of width $\sim 2000$ km s$^{-1}$ FWHM with the peak at the systemic redshift (the intermediate line region, or ILR), and another of width $\geq 7000$ km s$^{-1}$ FWHM and blueshifted by $\geq 1000$ km s$^{-1}$ (the very broad line region, or VBLR. We have suggested that the ILR is an inner extension of the narrow line region (NLR).
The ILR line intensity ratios differ from those of the VBLR. Varying the contribution of the ILR relative to the VBLR component accounts for much of the diversity of broad line profiles, including these reported correlations with line width, a measure of the ILR to VBLR ratio:
1. The strong negative correlations of equivalent width (EW) with FWHM for C IV $\lambda$1549 and Ly\,$\alpha$.
2. The positive correlation of EW with FWHM for the $\lambda$1400 feature.
3. The negative correlation of the Ly\,$\alpha$/C IV with FWHM.
4. The positive correlation of the $\lambda$1400/C\,IV with FWHM.
5. The negative correlation of C IV ``peakiness'' with FWHM.
6. The increasing blueshift of C III] and C IV with increasing FWHM.
7. The form of the dependence of C IV line asymmetry with FWHM.
Comparison with other AGN emission line regions shows that the ILR spectrum indicates coniditions intermediate between those of the VBLR and that of gas more distant from the ionizing continuum, such as the NLR and extended Ly~$\alpha$ nebulosity. Photoionization models suggest that, compared with the VBLR, the ILR is about ten times more distant from the ionizing continuum ($\sim$ 1 pc), 100 -- 1000 times less dense (10$^{10}$ cm$^{-3}$), and has a smaller covering factor ($\leq$ 3\%, compared with $\sim$ 24\% for the VBLR).
