Very High Density Clumps and Outflowing Winds in QSO Broad-Line Regions

Abstract

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 dif­ fering mixtures of different gas components. Six of these seven objects have unusually narrow BELR profiles, which greatly facilitates the disentangling of blends and measuring of weak lines. In the QSO 0207 398, the BELR is made up of at least three kinematically distinct components; its spectrum is in fact a composite of the spectra of the more homogeneous BELRs in the QSOs at either end of our sequence of properties. This paper focuses on the properties of the line-emitting region in Q0207 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 (nH � 1012·5 em 3) gas at a characteristic radius r � 101 7· 7 em from the continuum source and which emits a low-ionization spectrum including strong AI III A. 1857. The second component, B, in Q0207 398 is the subject of a companion paper. It is characterized by high-ionization lines such as N v A.1240, 0 VI A.1034, and C IV A.1 549 with profiles that peak at zero velocity but have a blue tail extending out to 1 1 ,000 km s -1• It receives about the same incident flux as component A and therefore may lie at the same distance from the continuum source, but it is signifi­ cantly less dense (nH � 1011 em 3). The remaining line emission from Q0207 398 is attributed to a component C which has reason­ ably brbad (FWHM = 2000 km s1 ), symmetric line profiles centered at zero velocity. Most of the Lyct and C III] A. 1909 emission comes from this region, but it also contributes 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 component A as the dense source for radiatively accelerated, outward flowing gas which we see as component B. Component A may consist of the ablated atmospheres of stars which have strayed too close to the QSO nucleus. In addition, component A's velocity width is essentially the same as that of the stellar population in the nucleus of M87. From the radius and velocity, we infer the pres­ ence of a central mass of only 10 7-108 M 8, if we are measuring virial motions and if the ionizing contin­ uum is isotropic. An alternate possibility is that the narrow single-peaked component A profile comes from a rotating torus/accretion disk, probably seen face-on, in which case it is impossible to measure the central mass. We discuss the similarity between Mg II-type broad absorption line (BAL) QSOs and Q0207 398, which does not have BALs. In fact, the two Mg n-type BAL objects in our sample have spectra almost exactly like that of Q0207 398, except that component B is seen in absorption rather than in emission. Subject headings: line : profiles quasars : emission lines quasars: individual (Q0207 398)