Galaxies and the Universe - Accretion and Outflow in AGN

Galaxies and the Universe - Accretion and Outflow in AGN -...

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1/15/12 Gala[ieV and Whe UniYeuVe - AccueWion and OXWfloZ in AGN 1/5 ZZZ.aVWu.Xa.edX/keel/gala[ieV/inandoXW.hWml Accretion and Outflow in Active Galactic Nuclei BUoad-AbVoUpWion-Line QSOV Some QSOs show very broad blueshifted absorption troughs associated with strong UV resonance lines. The type example is PHL 5200, shown in Fig. 1 of Junkkarinen, Burbidge, and Smith 1983 (ApJ 265, 51, ADS by permission of the AAS): The properties of these systems have been reviewed by Weymann, Turnshek, and Christiansen 1984 (in Astroph\sics of Active Gala[ies and Quasars , p. 333), Weymann and Foltz 1983 (Liege Astrophysical Coll., p. 538), Turnshek 1984 (ApJ 280, 51) and Turnshek 1988 (in QSO Absorption Lines; Probing the Universe , p. 17). Salient features of these spectra include: velocities up to 3 × 10 4 km/s with respect to the emission-line peak occurrence in 3-10% of high-redshift QSOs weak absorption at Lyman Į strong absorption in C IV, Si IV, N V, O VI some show absorption from excited states of Fe II some evidence for slightly different emission-line ratios than non-BAL objects QSOs with strong BAL systems are all radio-quiet they are apparently more strongly polarized and more variable than non-BAL QSOs Broad absorption lines are direct evidence of outflow from AGNs, at very respectable velocities. The primary questions are then (1) what is this absorbing region and (2) is the BAL phenomenon an intrinsic property of a few QSOs or do most QSOs look like this if viewed from certain directions? The BAL region is likely broadly similar in scale to (if necessarily a bit larger than) the BLR - the velocities, occurrence of excited states in absorption, and lack of absorption from such transitions as [O III] all suggest this. If the phenomenon is intrinsic, the covering factor of this cloud population is near unity, while if it is an orientation
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1/15/12 Gala[ieV and Whe UniYeuVe - AccueWion and OXWfloZ in AGN 2/5 ZZZ.aVWu.Xa.edX/keel/gala[ieV/inandoXW.hWml effect, the covering factor is of order the ratio of BAL QSOs to all QSOs in a mythical unbiased sample (as high as 10% if typical sets of QSOs are representative). The flow (or clouds) must be at least slightly outside the BLR since some broad lines are strongly absorbed. Correlations between BAL occurrence and line profiles in N V indicate that some of the BLR is coextensive with the BALR. Radiation pressure is a popularly invoked driver for the outflow, though it is still not clear whether the flow is accelerating or decelerating across the region we see. That is, the question is whether the highest velocities are at the inside or outside of the flow. Answering this is
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Galaxies and the Universe - Accretion and Outflow in AGN -...

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