VERY HIGH-DENSITY CLUMPS AND OUTFLOWING WINDS IN QSO BROAD-LINE REGIONS

Intercomparison of the spectra of seven high-luminosity quasi-stellar objects (QSOs) shows that there is a gradation of properties in their broad emission-line regions (BELRs) that can be understood as differin g mixtures of different gas components. Six of these seven objects hav e unusually narrow BELR profiles, which greatly facilitates the disent angling of blends and measuring of weak lines, In the QSO 0207-398, th e BELR is made up of at least three kinematically distinct components; its spectrum is in fact a composite of the spectra of the more homoge neous BELRs in the QSOs at either end of our sequence of properties. T his paper focuses on the properties of the line-emitting region in Q02 07-398 dubbed component ''A,'' which has sharp (FWHM = 1000 km s(-1)), symmetric line profiles centered at zero velocity. We find that these lines are emitted in very dense (n(H) similar to 10(12.5) cm(-3)) gas at a characteristic radius r similar to 10(17.7) cm from the continuu m source and which emits a low-ionization spectrum including strong Al III lambda 1857. The second component, ''B,'' in Q0207-398 is the sub ject of a companion paper. It is characterized by high-ionization line s such as N V lambda 1240, O VI lambda 1034, and C IV lambda 1549 with profiles that peak at zero velocity but have a blue tail extending ou t to -11,000 km s(-1). It receives about the same incident flux as com ponent A and therefore may lie at the same distance from the continuum source, but it is significantly less dense (n(H) similar to 10(11) cm (-3)). The remaining line emission from Q0207-398 is attributed to a c omponent ''C'' which has reasonably broad (FWHM = 2000 km s(-1)), symm etric line profiles centered at zero velocity. Most of the Ly alpha an d C III] lambda 1909 emission comes from this region, but it also cont ributes to C IV, N V, and many other lines. The spectrum of component C is in fact quite similar to that of ''normal'' QSOs. We interpret co mponent A as the dense source for radiatively accelerated, outward flo wing gas which we see as component B. Component A may consist of the a blated atmospheres of stars which have strayed too close to the QSO nu cleus. In addition, component A's velocity width is essentially the sa me as that of the stellar population in the nucleus of M87. From the r adius and velocity, we infer the presence of a central mass of only 10 (7)-10(8) M., if we are measuring virial motions and if the ionizing c ontinuum is isotropic. An alternate possibility is that the narrow sin gle-peaked component A profile comes from a rotating torus/accretion d isk, probably seen face-on, in which case it is impossible to measure the central mass. We discuss the similarity between Mg II-type broad a bsorption line (BAL) QSOs and Q0207-398, which does not have BALs. In fact, the two Mg II-type BAL objects in our sample have spectra almost exactly like that of Q0207-398, except that component B is seen in ab sorption rather than in emission.