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Testing quasar unification: radiative transfer in clumpy winds

Testing quasar unification: radiative transfer in clumpy winds
Testing quasar unification: radiative transfer in clumpy winds
Various unification schemes interpret the complex phenomenology of quasars and luminous active galactic nuclei (AGN) in terms of a simple picture involving a central black hole, an accretion disc and an associated outflow. Here, we continue our tests of this paradigm by comparing quasar spectra to synthetic spectra of biconical disc wind models, produced with our state-of-the-art Monte Carlo radiative transfer code. Previously, we have shown that we could produce synthetic spectra resembling those of observed broad absorption line (BAL) quasars, but only if the X-ray luminosity was limited to 1043 erg s-1. Here, we introduce a simple treatment of clumping, and find that a filling factor of ~0.01 moderates the ionization state sufficiently for BAL features to form in the rest-frame UV at more realistic X-ray luminosities. Our fiducial model shows good agreement with AGN X-ray properties and the wind produces strong line emission in, e.g., Lyα and CIV 1550 Å at low inclinations. At high inclinations, the spectra possess prominent LoBAL features. Despite these successes, we cannot reproduce all emission lines seen in quasar spectra with the correct equivalent-width ratios, and we find an angular dependence of emission line equivalent width despite the similarities in the observed emission line properties of BAL and non-BAL quasars. Overall, our work suggests that biconical winds can reproduce much of the qualitative behaviour expected from a unified model, but we cannot yet provide quantitative matches with quasar properties at all viewing angles. Whether disc winds can successfully unify quasars is therefore still an open question.
0035-8711
293-305
Matthews, J.H.
8aa37525-32b9-460c-bb83-01c89269ac31
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Long, K.S.
91417b3d-d408-475a-8907-eec131e17c66
Sim, S.A.
47872a86-d736-4351-af2f-83b2a4b987ef
Higginbottom, N.
4262c174-f544-4016-99d3-863fde9d9c73
Mangham, S.A.
c2053240-de45-4451-8cad-213930722d2e
Matthews, J.H.
8aa37525-32b9-460c-bb83-01c89269ac31
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Long, K.S.
91417b3d-d408-475a-8907-eec131e17c66
Sim, S.A.
47872a86-d736-4351-af2f-83b2a4b987ef
Higginbottom, N.
4262c174-f544-4016-99d3-863fde9d9c73
Mangham, S.A.
c2053240-de45-4451-8cad-213930722d2e

Matthews, J.H., Knigge, C., Long, K.S., Sim, S.A., Higginbottom, N. and Mangham, S.A. (2016) Testing quasar unification: radiative transfer in clumpy winds. Monthly Notices of the Royal Astronomical Society, 458 (1), 293-305. (doi:10.1093/mnras/stw323).

Record type: Article

Abstract

Various unification schemes interpret the complex phenomenology of quasars and luminous active galactic nuclei (AGN) in terms of a simple picture involving a central black hole, an accretion disc and an associated outflow. Here, we continue our tests of this paradigm by comparing quasar spectra to synthetic spectra of biconical disc wind models, produced with our state-of-the-art Monte Carlo radiative transfer code. Previously, we have shown that we could produce synthetic spectra resembling those of observed broad absorption line (BAL) quasars, but only if the X-ray luminosity was limited to 1043 erg s-1. Here, we introduce a simple treatment of clumping, and find that a filling factor of ~0.01 moderates the ionization state sufficiently for BAL features to form in the rest-frame UV at more realistic X-ray luminosities. Our fiducial model shows good agreement with AGN X-ray properties and the wind produces strong line emission in, e.g., Lyα and CIV 1550 Å at low inclinations. At high inclinations, the spectra possess prominent LoBAL features. Despite these successes, we cannot reproduce all emission lines seen in quasar spectra with the correct equivalent-width ratios, and we find an angular dependence of emission line equivalent width despite the similarities in the observed emission line properties of BAL and non-BAL quasars. Overall, our work suggests that biconical winds can reproduce much of the qualitative behaviour expected from a unified model, but we cannot yet provide quantitative matches with quasar properties at all viewing angles. Whether disc winds can successfully unify quasars is therefore still an open question.

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Accepted/In Press date: 8 February 2016
e-pub ahead of print date: 15 February 2016
Published date: 1 May 2016
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 396288
URI: http://eprints.soton.ac.uk/id/eprint/396288
ISSN: 0035-8711
PURE UUID: 5d85cabc-603a-48dd-b660-a14ed4f6eab2
ORCID for S.A. Mangham: ORCID iD orcid.org/0000-0001-7511-5652

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Date deposited: 07 Jun 2016 14:23
Last modified: 16 Dec 2019 19:53

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