We report on an analysis of a sample of objects observed to have a correlation between FWHM and critical density for de-excitation of forbidden emission lines. Included in the sample is a QSO of MV ≈ – 26 which is the most luminous object to date known to show such a relationship. In addition, this QSO shows that the semi-forbidden lines which arise in the Broad Line Region (BLR) follow the same trend seen in the more distant Narrow Line Region (NLR), suggesting that a smooth velocity field joins both zones. A similar relationship between linewidth and critical density holds for all objects in the sample despite a range of ≈ 5000:1 in luminosity.
Previous studies of the velocity field in NLRs of low redshift AGNs suggested that the physical processes are at work in all objects (Fillipenko 1985). We have extended the early work by obtaining a sample of objects from the literature which show a correlation between linewidth and critical density and supplemented these with data for a QSO recently discovered to show the first direct evidence for such a relationship extending into the BLR itself.