PG 0946+301: the Rosetta Stone of BALQSOs? Page: 4 of 10
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1.. Introduction
Broad Absorption Line (BAL) QSOs are the main manifestation of AGN outflows.
BALs are associated with prominent resonance lines such as C IV A1549, Si IV A1397, N V
A1240, and Lya A1215. They appear in about 10% of all quasars (Foltz et al. 1990) with
typical velocity widths of ~ 10, 000 km s- (Weymann, Turnshek, & Christiansen 1985;
Turnshek 1988) and terminal velocities of up to 50,000 km s-1. The small percentage of
BALQSOs among quasars is generally interpreted as an orientation effect, and it is probable
that the majority of quasars and other types of AGN harbor intrinsic outflows (Weymann
et al. 1991). In figure 1 we show the spectrum of PG 0946+301 which is a typical high
ionization BALQSO.
600 800 1000 rest 1200 1400 1600
_5 wavelength
0 VI 1034 Lya
4i O- IV 789 C IV 1549
U
Si IV 1397
' 30
I)2
0
xl
0 D_................................... V............ . .V.._.
1500 2000 2500 3000 3500
observed wavelength (t)
Fig. 1.- HST and ground-based data for PG 0946+301 (z = 1.22), where the BALs (some
of which are identified at the bottom) arise from an outflow with Av - 10, 000 km s-1.
Establishing the physical properties of the flow by determining the ionization
equilibrium and abundances (IEA) of the BAL material is a fundamental issue in BALQSOs
studies. Furthermore, such determinations are powerful probes of abundances in the entire
AGN environment. Inferences about the IEA in the BAL region are derived by trying to
simulate BAL ionic-column-densities (N;,) using photoionization codes. Several groups
(Korista et al. 1996; Turnshek et al. 1996; Hamann 1996) have used extracted N,, from
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Arav, N., LLNL. PG 0946+301: the Rosetta Stone of BALQSOs?, article, June 1, 1998; California. (https://digital.library.unt.edu/ark:/67531/metadc677399/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.