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Unravelling the physics of multiphase AGN winds through emission line tracers

Richings, Alexander J.; Faucher-Giguère, Claude André; Stern, Jonathan

Authors

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Dr Alex Richings A.J.Richings@hull.ac.uk
Lecturer in Data Science, Artificial Intelligence and Modelling

Claude André Faucher-Giguère

Jonathan Stern



Abstract

Observations of emission lines in active galactic nuclei (AGNs) often find fast (∼1000 km s−1) outflows extending to kiloparsec scales, seen in ionized, neutral atomic and molecular gas. In this work we present radiative transfer calculations of emission lines in hydrodynamic simulations of AGN outflows driven by a hot wind bubble, including non-equilibrium chemistry, to explore how these lines trace the physical properties of the multiphase outflow. We find that the hot bubble compresses the line-emitting gas, resulting in higher pressures than in the ambient interstellar medium or that would be produced by the AGN radiation pressure. This implies that observed emission line ratios such as [O IV]25 μm/[Ne II]12 μm, [Ne V]14 μm/[Ne II]12 μm, and [N III]57 μm/[N II]122 μm constrain the presence of the bubble and hence the outflow driving mechanism. However, the line-emitting gas is under-pressurized compared to the hot bubble itself, and much of the line emission arises from gas that is out of pressure, thermal and/or chemical equilibrium. Our results thus suggest that assuming equilibrium conditions, as commonly done in AGN line emission models, is not justified if a hot wind bubble is present. We also find that ≳50 per cent of the mass outflow rate, momentum flux, and kinetic energy flux of the outflow are traced by lines such as [N II]122 μm and [Ne III]15 μm (produced in the 104 K phase) and [C II]158 μm (produced in the transition from 104 K to 100 K).

Citation

Richings, A. J., Faucher-Giguère, C. A., & Stern, J. (2021). Unravelling the physics of multiphase AGN winds through emission line tracers. Monthly notices of the Royal Astronomical Society, 503(2), 1568-1585. https://doi.org/10.1093/mnras/stab556

Journal Article Type Article
Acceptance Date Feb 20, 2021
Online Publication Date Feb 27, 2021
Publication Date May 1, 2021
Deposit Date Nov 28, 2022
Publicly Available Date Mar 28, 2024
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 503
Issue 2
Pages 1568-1585
DOI https://doi.org/10.1093/mnras/stab556
Keywords Astrochemistry; Galaxies: active; Quasars: emission lines; Quasars: general
Public URL https://hull-repository.worktribe.com/output/4132487
Publisher URL https://academic.oup.com/mnras/article/503/2/1568/6153871

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Publisher Licence URL
http://creativecommons.org/licenses/by/4.0

Copyright Statement
© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.




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