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The reverberation signatures of rotating disc winds in active galactic nuclei

The reverberation signatures of rotating disc winds in active galactic nuclei
The reverberation signatures of rotating disc winds in active galactic nuclei
The broad emission lines (BELs) in active galactic nuclei (AGN) respond to ionizing continuum variations. The time and velocity dependence of their response depends on the structure of the broad-line region: its geometry, kinematics and ionization state. Here, we predict the reverberation signatures of BELs formed in rotating accretion disc winds. We use a Monte Carlo radiative transfer and ionization code to predict velocity-delay maps for representative high- (C$~IV$) and low-ionization (H$\alpha$) emission lines in both high- and moderate-luminosity AGN. Self-shielding, multiple scattering and the ionization structure of the outflows are all self-consistently taken into account, while small-scale structure in the outflow is modelled in the micro-clumping approximation. Our main findings are: (1) The velocity-delay maps of smooth/micro-clumped outflows often contain significant negative responses. (2)~The reverberation signatures of disc wind models tend to be rotation dominated and can even resemble the classic "red-leads-blue" inflow signature. (3) Traditional "blue-leads-red" outflow signatures can usually only be observed in the long-delay limit. (4) Our models predict lag-luminosity relationships similar to those inferred from observations, but systematically underpredict the observed centroid delays. (5) The ratio between "virial product" and black hole mass predicted by our models depends on viewing angle. Our results imply that considerable care needs to be taken in interpreting data obtained by observational reverberation mapping campaigns. In particular, basic signatures such as "red-leads-blue", "blue-leads-red" and "blue and red vary jointly" are not always reliable indicators of inflow, outflow or rotation. This may help to explain the perplexing diversity of such signatures seen in observational campaigns to date.
astro-ph.GA
0035-8711
4788-4801
Mangham, S.W.
c2053240-de45-4451-8cad-213930722d2e
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Matthews, J.H.
8aa37525-32b9-460c-bb83-01c89269ac31
Long, K.S.
839b3509-5ef3-4126-97fa-912e3357d8ef
Sim, S.A.
7df85a4e-ebca-4700-b95c-90a6427985ea
Higginbottom, N.
c542dcc3-7227-48ca-b50f-fd989eedd8fb
Mangham, S.W.
c2053240-de45-4451-8cad-213930722d2e
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Matthews, J.H.
8aa37525-32b9-460c-bb83-01c89269ac31
Long, K.S.
839b3509-5ef3-4126-97fa-912e3357d8ef
Sim, S.A.
7df85a4e-ebca-4700-b95c-90a6427985ea
Higginbottom, N.
c542dcc3-7227-48ca-b50f-fd989eedd8fb

Mangham, S.W., Knigge, C., Matthews, J.H., Long, K.S., Sim, S.A. and Higginbottom, N. (2017) The reverberation signatures of rotating disc winds in active galactic nuclei. Monthly Notices of the Royal Astronomical Society, 471 (4), 4788-4801. (doi:10.1093/mnras/stx1863).

Record type: Article

Abstract

The broad emission lines (BELs) in active galactic nuclei (AGN) respond to ionizing continuum variations. The time and velocity dependence of their response depends on the structure of the broad-line region: its geometry, kinematics and ionization state. Here, we predict the reverberation signatures of BELs formed in rotating accretion disc winds. We use a Monte Carlo radiative transfer and ionization code to predict velocity-delay maps for representative high- (C$~IV$) and low-ionization (H$\alpha$) emission lines in both high- and moderate-luminosity AGN. Self-shielding, multiple scattering and the ionization structure of the outflows are all self-consistently taken into account, while small-scale structure in the outflow is modelled in the micro-clumping approximation. Our main findings are: (1) The velocity-delay maps of smooth/micro-clumped outflows often contain significant negative responses. (2)~The reverberation signatures of disc wind models tend to be rotation dominated and can even resemble the classic "red-leads-blue" inflow signature. (3) Traditional "blue-leads-red" outflow signatures can usually only be observed in the long-delay limit. (4) Our models predict lag-luminosity relationships similar to those inferred from observations, but systematically underpredict the observed centroid delays. (5) The ratio between "virial product" and black hole mass predicted by our models depends on viewing angle. Our results imply that considerable care needs to be taken in interpreting data obtained by observational reverberation mapping campaigns. In particular, basic signatures such as "red-leads-blue", "blue-leads-red" and "blue and red vary jointly" are not always reliable indicators of inflow, outflow or rotation. This may help to explain the perplexing diversity of such signatures seen in observational campaigns to date.

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Accepted/In Press date: 19 July 2017
e-pub ahead of print date: 22 July 2017
Published date: November 2017
Keywords: astro-ph.GA

Identifiers

Local EPrints ID: 412911
URI: http://eprints.soton.ac.uk/id/eprint/412911
ISSN: 0035-8711
PURE UUID: 4baefbf6-6a10-4ccd-a5a1-db98486efa19
ORCID for S.W. Mangham: ORCID iD orcid.org/0000-0001-7511-5652

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Date deposited: 08 Aug 2017 16:31
Last modified: 06 Oct 2020 19:38

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