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Line-driven disk winds in active galactic nuclei: the critical importance of ionization and radiative transfer

Line-driven disk winds in active galactic nuclei: the critical importance of ionization and radiative transfer
Line-driven disk winds in active galactic nuclei: the critical importance of ionization and radiative transfer
Accretion disk winds are thought to produce many of the characteristic features seen in the spectra of active galactic nuclei (AGNs) and quasi-stellar objects (QSOs). These outflows also represent a natural form of feedback between the central supermassive black hole and its host galaxy. The mechanism for driving this mass loss remains unknown, although radiation pressure mediated by spectral lines is a leading candidate. Here, we calculate the ionization state of, and emergent spectra for, the hydrodynamic simulation of a line-driven disk wind previously presented by Proga & Kallman. To achieve this, we carry out a comprehensive Monte Carlo simulation of the radiative transfer through, and energy exchange within, the predicted outflow. We find that the wind is much more ionized than originally estimated. This is in part because it is much more difficult to shield any wind regions effectively when the outflow itself is allowed to reprocess and redirect ionizing photons. As a result, the calculated spectrum that would be observed from this particular outflow solution would not contain the ultraviolet spectral lines that are observed in many AGN/QSOs. Furthermore, the wind is so highly ionized that line driving would not actually be efficient. This does not necessarily mean that line-driven winds are not viable. However, our work does illustrate that in order to arrive at a self-consistent model of line-driven disk winds in AGN/QSO, it will be critical to include a more detailed treatment of radiative transfer and ionization in the next generation of hydrodynamic simulations.
0004-637X
1-12
Higginbottom, Nick
99609bfd-0a53-4110-b099-6b23fbc1044e
Proga, Daniel
dda41138-6783-4046-b71e-bc8cdc064bc2
Knigge, Christian
ac320eec-631a-426e-b2db-717c8bf7857e
Long, Knox S.
2195d0ac-518d-4738-8e89-3e8e7a035a6c
Matthews, James H.
8aa37525-32b9-460c-bb83-01c89269ac31
Sim, Stuart A.
67bb8102-b981-4e2e-9617-8c7806ef1329
Higginbottom, Nick
99609bfd-0a53-4110-b099-6b23fbc1044e
Proga, Daniel
dda41138-6783-4046-b71e-bc8cdc064bc2
Knigge, Christian
ac320eec-631a-426e-b2db-717c8bf7857e
Long, Knox S.
2195d0ac-518d-4738-8e89-3e8e7a035a6c
Matthews, James H.
8aa37525-32b9-460c-bb83-01c89269ac31
Sim, Stuart A.
67bb8102-b981-4e2e-9617-8c7806ef1329

Higginbottom, Nick, Proga, Daniel, Knigge, Christian, Long, Knox S., Matthews, James H. and Sim, Stuart A. (2014) Line-driven disk winds in active galactic nuclei: the critical importance of ionization and radiative transfer. The Astrophysical Journal, 789 (1), 1-12, [19]. (doi:10.1088/0004-637X/789/1/19).

Record type: Article

Abstract

Accretion disk winds are thought to produce many of the characteristic features seen in the spectra of active galactic nuclei (AGNs) and quasi-stellar objects (QSOs). These outflows also represent a natural form of feedback between the central supermassive black hole and its host galaxy. The mechanism for driving this mass loss remains unknown, although radiation pressure mediated by spectral lines is a leading candidate. Here, we calculate the ionization state of, and emergent spectra for, the hydrodynamic simulation of a line-driven disk wind previously presented by Proga & Kallman. To achieve this, we carry out a comprehensive Monte Carlo simulation of the radiative transfer through, and energy exchange within, the predicted outflow. We find that the wind is much more ionized than originally estimated. This is in part because it is much more difficult to shield any wind regions effectively when the outflow itself is allowed to reprocess and redirect ionizing photons. As a result, the calculated spectrum that would be observed from this particular outflow solution would not contain the ultraviolet spectral lines that are observed in many AGN/QSOs. Furthermore, the wind is so highly ionized that line driving would not actually be efficient. This does not necessarily mean that line-driven winds are not viable. However, our work does illustrate that in order to arrive at a self-consistent model of line-driven disk winds in AGN/QSO, it will be critical to include a more detailed treatment of radiative transfer and ionization in the next generation of hydrodynamic simulations.

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Accepted/In Press date: 12 May 2014
e-pub ahead of print date: 10 June 2014
Published date: 10 June 2014
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 402024
URI: http://eprints.soton.ac.uk/id/eprint/402024
ISSN: 0004-637X
PURE UUID: 99465c34-cc03-44dd-86df-1a19bd22a519

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Date deposited: 26 Oct 2016 14:13
Last modified: 19 Jan 2021 17:30

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Author: Nick Higginbottom
Author: Daniel Proga
Author: Knox S. Long
Author: James H. Matthews
Author: Stuart A. Sim

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