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A disc wind model for blueshifts in quasar broad emission lines

A disc wind model for blueshifts in quasar broad emission lines
A disc wind model for blueshifts in quasar broad emission lines

Blueshifts - or, more accurately, blue asymmetries - in broad emission lines such as C iv λ1550 are common in luminous quasars and correlate with fundamental properties such as Eddington ratio and broad absorption line (BAL) characteristics. However, the formation of these blueshifts is still not understood, and neither is their physical connection to the BAL phenomenon or accretion disc. In this work, we present Monte Carlo radiative transfer and photoionization simulations using parametrized biconical disc-wind models. We take advantage of the azimuthal symmetry of a quasar and show that we can reproduce C iv blueshifts provided that (i) the disc-mid-plane is optically thick out to radii beyond the line formation region, so that the receding wind bicone is obscured; and (ii) the system is viewed from relatively low (that is, more face-on) inclinations (≤40°). We show that C iv emission-line blueshifts and BALs can form in the same wind structure. The velocity profile of the wind has a significant impact on the location of the line formation region and the resulting line profile, suggesting that the shape of the emission lines can be used as a probe of wind-driving physics. While we are successful at producing blueshifts/blue asymmetries in outflows, we struggle to match the detailed shape or skew of the observed emission-line profiles. In addition, our models produce redshifted emission-line asymmetries for certain viewing angles. We discuss our work in the context of the C iv λ1550 emission blueshift versus equivalent-width space and explore the implications for quasar disc wind physics.

astro-ph.GA, astro-ph.HE, quasars: emission lines, quasars: general, line: formation, galaxies: active, radiative transfer, accretion, accretion discs
1365-2966
3967–3986
Matthews, James H.
8aa37525-32b9-460c-bb83-01c89269ac31
Strong-Wright, Jago
34cb428f-381d-4395-bd5e-15e9de3ea0c1
Knigge, Christian
ac320eec-631a-426e-b2db-717c8bf7857e
Hewett, Paul
a4763f70-9f9a-4a4e-85ed-10694a66e5c9
Temple, Matthew J.
7bbe5840-3c09-445a-81f7-e090d01ff411
Long, Knox S.
e749f6fb-96dc-489b-aa2c-86151f4ff579
Rankine, Amy L.
88010438-646c-44d2-95a3-2d9ada0a07eb
Stepney, Matthew
b769a5cf-0fda-4c4c-8e9d-e29c63e4f62a
Banerji, Manda
ce0a04bf-70a4-4b64-9027-b1a01def7325
Richards, Gordon T.
0192698b-f415-4a89-9ea5-cd5f74a87755
Matthews, James H.
8aa37525-32b9-460c-bb83-01c89269ac31
Strong-Wright, Jago
34cb428f-381d-4395-bd5e-15e9de3ea0c1
Knigge, Christian
ac320eec-631a-426e-b2db-717c8bf7857e
Hewett, Paul
a4763f70-9f9a-4a4e-85ed-10694a66e5c9
Temple, Matthew J.
7bbe5840-3c09-445a-81f7-e090d01ff411
Long, Knox S.
e749f6fb-96dc-489b-aa2c-86151f4ff579
Rankine, Amy L.
88010438-646c-44d2-95a3-2d9ada0a07eb
Stepney, Matthew
b769a5cf-0fda-4c4c-8e9d-e29c63e4f62a
Banerji, Manda
ce0a04bf-70a4-4b64-9027-b1a01def7325
Richards, Gordon T.
0192698b-f415-4a89-9ea5-cd5f74a87755

Matthews, James H., Strong-Wright, Jago, Knigge, Christian, Hewett, Paul, Temple, Matthew J., Long, Knox S., Rankine, Amy L., Stepney, Matthew, Banerji, Manda and Richards, Gordon T. (2023) A disc wind model for blueshifts in quasar broad emission lines. Monthly Notices of the Royal Astronomical Society, 526 (3), 3967–3986. (doi:10.1093/mnras/stad2895).

Record type: Article

Abstract

Blueshifts - or, more accurately, blue asymmetries - in broad emission lines such as C iv λ1550 are common in luminous quasars and correlate with fundamental properties such as Eddington ratio and broad absorption line (BAL) characteristics. However, the formation of these blueshifts is still not understood, and neither is their physical connection to the BAL phenomenon or accretion disc. In this work, we present Monte Carlo radiative transfer and photoionization simulations using parametrized biconical disc-wind models. We take advantage of the azimuthal symmetry of a quasar and show that we can reproduce C iv blueshifts provided that (i) the disc-mid-plane is optically thick out to radii beyond the line formation region, so that the receding wind bicone is obscured; and (ii) the system is viewed from relatively low (that is, more face-on) inclinations (≤40°). We show that C iv emission-line blueshifts and BALs can form in the same wind structure. The velocity profile of the wind has a significant impact on the location of the line formation region and the resulting line profile, suggesting that the shape of the emission lines can be used as a probe of wind-driving physics. While we are successful at producing blueshifts/blue asymmetries in outflows, we struggle to match the detailed shape or skew of the observed emission-line profiles. In addition, our models produce redshifted emission-line asymmetries for certain viewing angles. We discuss our work in the context of the C iv λ1550 emission blueshift versus equivalent-width space and explore the implications for quasar disc wind physics.

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Accepted/In Press date: 18 September 2023
e-pub ahead of print date: 28 September 2023
Published date: 1 December 2023
Additional Information: Funding Information: We thank the referee for reviewing our paper and their constructive comments. We would like to thank Andrew Sellek, Stuart Sim, Nico Scepi, and Teo Muñoz-Darias for helpful discussions. JM acknowledges support from a Royal Society University Research Fellowship and, previously, the Herchel Smith fund. ALR acknowledges support from a UKRI Future Leaders Fellowship (grant MR/T020989/1). MJT acknowledges support from a FONDECYT postdoctoral fellowship (3220516). This work was performed using resources provided by the Cambridge Service for Data Driven Discovery (CSD3) operated by the University of Cambridge Research Computing Service ( www.csd3.cam.ac.uk ), provided by Dell EMC and Intel using Tier-2 funding from the Engineering and Physical Sciences Research Council (capital grant EP/T022159/1), and DiRAC funding from the Science and Technology Facilities Council ( www.dirac.ac.uk ). We gratefully acknowledge the use of the following software packages: OpenMPI (Gabriel et al. ), matplotlib (Hunter ), and astropy (Astropy Collaboration , ). For the purpose of open access, the authors have applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising from this submission. Funding Information: Funding for the SDSS IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. SDSS-IV acknowledges support and resources from the Center for High Performance Computing at the University of Utah. The SDSS website is www.sdss4.org . SDSS-IV is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration including the Brazilian Participation Group, the Carnegie Institution for Science, Carnegie Mellon University, Center for Astrophysics| Harvard & Smithsonian, the Chilean Participation Group, the French Participation Group, Instituto de Astrofísica de Canarias, The Johns Hopkins University, Kavli Institute for the Physics and Mathematics of the Universe (IPMU)/University of Tokyo, the Korean Participation Group, Lawrence Berkeley National Laboratory, Leibniz Institut für Astrophysik Potsdam (AIP), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Max-Planck-Institut für Astrophysik (MPA Garching), Max-Planck-Institut für Extraterrestrische Physik (MPE), National Astronomical Observatories of China, New Mexico State University, New York University, University of Notre Dame, Observatário Nacional/MCTI, The Ohio State University, Pennsylvania State University, Shanghai Astronomical Observatory, United Kingdom Participation Group, Universidad Nacional Autónoma de México, University of Arizona, University of Colorado Boulder, University of Oxford, University of Portsmouth, University of Utah, University of Virginia, University of Washington, University of Wisconsin, Vanderbilt University, and Yale University. Publisher Copyright: © 2023 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.
Keywords: astro-ph.GA, astro-ph.HE, quasars: emission lines, quasars: general, line: formation, galaxies: active, radiative transfer, accretion, accretion discs

Identifiers

Local EPrints ID: 483051
URI: http://eprints.soton.ac.uk/id/eprint/483051
ISSN: 1365-2966
PURE UUID: 2248e9d2-f43d-4335-827d-dc9a38727854
ORCID for Manda Banerji: ORCID iD orcid.org/0000-0002-0639-5141

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Date deposited: 20 Oct 2023 16:51
Last modified: 18 Mar 2024 03:57

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Contributors

Author: James H. Matthews
Author: Jago Strong-Wright
Author: Paul Hewett
Author: Matthew J. Temple
Author: Knox S. Long
Author: Amy L. Rankine
Author: Matthew Stepney
Author: Manda Banerji ORCID iD
Author: Gordon T. Richards

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