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Quasar emission lines as probes of orientation: implications for disc wind geometries and unification

Quasar emission lines as probes of orientation: implications for disc wind geometries and unification
Quasar emission lines as probes of orientation: implications for disc wind geometries and unification
The incidence of broad absorption lines (BALs) in quasar samples is often interpreted in the context of a geometric unification model consisting of an accretion disc and an associated outflow. We use the Sloan Digital Sky Survey quasar sample to test this model by examining the equivalent widths (EWs) of C iv 1550 Å, Mg ii 2800 Å, [O iii] 5007 Å and C iii] 1909 Å. We find that the emission line EW distributions in BAL and non-BAL quasars are remarkably similar – a property that is inconsistent with scenarios in which a BAL outflow rises equatorially from a geometrically thin, optically thick accretion disc. We construct simple models to predict the distributions from various geometries; these models confirm the above finding and disfavour equatorial geometries. We show that obscuration, line anisotropy and general relativistic effects on the disc continuum are unlikely to hide an EW inclination dependence. We carefully examine the radio and polarization properties of BAL quasars. Both suggest that they are most likely viewed (on average) from intermediate inclinations, between type 1 and type 2 active galactic nuclei (AGN). We also find that the low-ionization BAL quasars in our sample are not confined to one region of the ‘Eigenvector 1’ parameter space. Overall, our work leads to one of the following conclusions, or some combination thereof: (i) the continuum does not emit like a geometrically thin, optically thick disc; (ii) BAL quasars are viewed from similar angles to non-BAL quasars, that is, low inclinations and (iii) geometric unification does not explain the fraction of BALs in quasar samples.
0035-8711
2571-2584
Matthews, J.H
2fa7b110-a2d9-40c0-adbe-2d049fc42ea6
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Long, K.S.
f513476b-7a04-477d-91be-d6bb71d94674
Matthews, J.H
2fa7b110-a2d9-40c0-adbe-2d049fc42ea6
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Long, K.S.
f513476b-7a04-477d-91be-d6bb71d94674

Matthews, J.H, Knigge, C. and Long, K.S. (2017) Quasar emission lines as probes of orientation: implications for disc wind geometries and unification. Monthly Notices of the Royal Astronomical Society, 467 (3), 2571-2584. (doi:10.1093/mnras/stx231).

Record type: Article

Abstract

The incidence of broad absorption lines (BALs) in quasar samples is often interpreted in the context of a geometric unification model consisting of an accretion disc and an associated outflow. We use the Sloan Digital Sky Survey quasar sample to test this model by examining the equivalent widths (EWs) of C iv 1550 Å, Mg ii 2800 Å, [O iii] 5007 Å and C iii] 1909 Å. We find that the emission line EW distributions in BAL and non-BAL quasars are remarkably similar – a property that is inconsistent with scenarios in which a BAL outflow rises equatorially from a geometrically thin, optically thick accretion disc. We construct simple models to predict the distributions from various geometries; these models confirm the above finding and disfavour equatorial geometries. We show that obscuration, line anisotropy and general relativistic effects on the disc continuum are unlikely to hide an EW inclination dependence. We carefully examine the radio and polarization properties of BAL quasars. Both suggest that they are most likely viewed (on average) from intermediate inclinations, between type 1 and type 2 active galactic nuclei (AGN). We also find that the low-ionization BAL quasars in our sample are not confined to one region of the ‘Eigenvector 1’ parameter space. Overall, our work leads to one of the following conclusions, or some combination thereof: (i) the continuum does not emit like a geometrically thin, optically thick disc; (ii) BAL quasars are viewed from similar angles to non-BAL quasars, that is, low inclinations and (iii) geometric unification does not explain the fraction of BALs in quasar samples.

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Quasar emission lines as probes of orientation - Accepted Manuscript
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Accepted/In Press date: 24 January 2017
e-pub ahead of print date: 27 January 2017
Published date: 27 January 2017

Identifiers

Local EPrints ID: 412477
URI: http://eprints.soton.ac.uk/id/eprint/412477
ISSN: 0035-8711
PURE UUID: e9f320f7-63e4-45ce-9ebe-5fcae21abf55

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Date deposited: 17 Jul 2017 13:56
Last modified: 06 Oct 2020 21:23

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