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Synthetic Absorption Lines for a Clumpy Medium: A Spectral Signature for Cloud Acceleration in AGN?There is increasing evidence that the highly ionized multiphase components of AGN disc winds may be due to thermal instability. The ions responsible for forming the observed X-ray absorption lines may only exist in relatively cool clumps that can be identified with the so-called warm absorbers. Here we calculate synthetic absorption lines for such warm absorbers from first principles by combining 2D hydrodynamic solutions of a two-phase medium with a dense grid of photoionization models to determine the detailed ionization structure of the gas. Our calculations reveal that cloud disruption, which leads to a highly complicated velocity field (i.e. a clumpy flow), will only mildly affect line shapes and strengths when the warm gas becomes highly mixed but not depleted. Prior to complete disruption, clouds that are optically thin to the driving UV resonance lines will cause absorption at an increasingly blueshifted line-of-sight velocity as they are accelerated. This behavior will imprint an identifiable signature on the line profile if warm absorbers are enshrouded in an even broader absorption line produced by a high column of intercloud gas. Interestingly, we show that it is possible to develop a spectral diagnostic for cloud acceleration by differencing the absorption components of a doublet line, a result that can be qualitatively understood using a simple partial covering model. Our calculations also permit us to comment on the spectral differences between cloud disruption and ionization changes driven by flux variability. Notably, cloud disruption offers another possibility for explaining absorption line variability.
Document ID
20170007934
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Waters, Tim
(Nevada Univ. Las Vegas, NV, United States)
Proga, Daniel
(Nevada Univ. Las Vegas, NV, United States)
Dannen, Randall
(Nevada Univ. Las Vegas, NV, United States)
Kallman, Timothy R.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Date Acquired
August 22, 2017
Publication Date
March 6, 2017
Publication Information
Publication: Monthly Notices of the Royal Astronomical Society
Publisher: Oxford University Press
Volume: 467
Issue: 3
Subject Category
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN45839
GSFC-E-DAA-TN45840
Funding Number(s)
CONTRACT_GRANT: NAS8-39073
Distribution Limits
Public
Copyright
Other
Keywords
line: formation – galaxies: nuclei – quasars: absorption lines

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