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A simple disc wind model for broad absorption line quasars

A simple disc wind model for broad absorption line quasars
A simple disc wind model for broad absorption line quasars
Approximately 20 per?cent of quasi-stellar objects (QSOs) exhibit broad, blue-shifted absorption lines in their ultraviolet spectra. Such features provide clear evidence for significant outflows from these systems, most likely in the form of accretion disc winds. These winds may represent the ‘quasar’ mode of feedback that is often invoked in galaxy formation/evolution models, and they are also key to unification scenarios for active galactic nuclei (AGN) and QSOs. To test these ideas, we construct a simple benchmark model of an equatorial, biconical accretion disc wind in a QSO and use a Monte Carlo ionization/radiative transfer code to calculate the ultraviolet spectra as a function of viewing angle. We find that for plausible outflow parameters, sightlines looking directly into the wind cone do produce broad, blue-shifted absorption features in the transitions typically seen in broad absorption line (BAL) QSOs. However, our benchmark model is intrinsically X-ray weak in order to prevent overionization of the outflow, and the wind does not yet produce collisionally excited line emission at the level observed in non-BAL QSOs. As a first step towards addressing these shortcomings, we discuss the sensitivity of our results to changes in the assumed X-ray luminosity and mass-loss rate, ?wind. In the context of our adopted geometry, ?wind ? ?acc is required in order to produce significant BAL features. The kinetic luminosity and momentum carried by such outflows would be sufficient to provide significant feedback.
0035-8711
1390-1407
Higginbottom, N.
67799e03-c140-4943-956c-58ef28ebd185
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Long, K. S.
839b3509-5ef3-4126-97fa-912e3357d8ef
Sim, S. A.
7df85a4e-ebca-4700-b95c-90a6427985ea
Matthews, J. H.
d2b4d130-4c32-4928-8649-417cefd965de
Higginbottom, N.
67799e03-c140-4943-956c-58ef28ebd185
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Long, K. S.
839b3509-5ef3-4126-97fa-912e3357d8ef
Sim, S. A.
7df85a4e-ebca-4700-b95c-90a6427985ea
Matthews, J. H.
d2b4d130-4c32-4928-8649-417cefd965de

Higginbottom, N., Knigge, C., Long, K. S., Sim, S. A. and Matthews, J. H. (2013) A simple disc wind model for broad absorption line quasars. Monthly Notices of the Royal Astronomical Society, 436 (2), 1390-1407. (doi:10.1093/mnras/stt1658).

Record type: Article

Abstract

Approximately 20 per?cent of quasi-stellar objects (QSOs) exhibit broad, blue-shifted absorption lines in their ultraviolet spectra. Such features provide clear evidence for significant outflows from these systems, most likely in the form of accretion disc winds. These winds may represent the ‘quasar’ mode of feedback that is often invoked in galaxy formation/evolution models, and they are also key to unification scenarios for active galactic nuclei (AGN) and QSOs. To test these ideas, we construct a simple benchmark model of an equatorial, biconical accretion disc wind in a QSO and use a Monte Carlo ionization/radiative transfer code to calculate the ultraviolet spectra as a function of viewing angle. We find that for plausible outflow parameters, sightlines looking directly into the wind cone do produce broad, blue-shifted absorption features in the transitions typically seen in broad absorption line (BAL) QSOs. However, our benchmark model is intrinsically X-ray weak in order to prevent overionization of the outflow, and the wind does not yet produce collisionally excited line emission at the level observed in non-BAL QSOs. As a first step towards addressing these shortcomings, we discuss the sensitivity of our results to changes in the assumed X-ray luminosity and mass-loss rate, ?wind. In the context of our adopted geometry, ?wind ? ?acc is required in order to produce significant BAL features. The kinetic luminosity and momentum carried by such outflows would be sufficient to provide significant feedback.

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e-pub ahead of print date: September 2013
Published date: December 2013
Organisations: Physics & Astronomy

Identifiers

Local EPrints ID: 369386
URI: http://eprints.soton.ac.uk/id/eprint/369386
ISSN: 0035-8711
PURE UUID: 103ef23e-3da8-48b7-98c2-413ba51341ce

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Date deposited: 25 Sep 2014 10:30
Last modified: 16 Dec 2019 20:23

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Contributors

Author: N. Higginbottom
Author: C. Knigge
Author: K. S. Long
Author: S. A. Sim
Author: J. H. Matthews

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