THE HST QUASAR ABSORPTION-LINE KEY PROJECT .9. AN EMISSION-LINE STUDYOF PG 2251+113

We present HST and quasi-simultaneous ground-based observations of the z = 0.3252 QSO PG 2251 + 113. We find a correlation between line widt hs and the critical density for de-excitation of the forbidden emissio n lines observed in this object. We can show that this correlation als o applies to the semiforbidden and possibly also the permitted lines w hich arise in the broad emission-line region. While this result was pr edicted from statistical studies, it has never previously been shown t o hold in detail in any individual object. This relationship between t he narrow and broad emission-line regions may help constrain dynamical models of both regions. We examine the implications of this result fo r a simple radial infall model of the emitting gas developed to explai n the origin of narrow-line profiles.