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Simulations of radiative turbulent mixing layers

Ji, Suoqing and Oh, S. Peng and Masterson, Phillip (2019) Simulations of radiative turbulent mixing layers. Monthly Notices of the Royal Astronomical Society, 487 (1). pp. 737-754. ISSN 0035-8711.

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Radiative turbulent mixing layers should be ubiquitous in multi-phase gas with shear flow. They are a potentially attractive explanation for the high ions such as O VI seen in high-velocity clouds and the circumgalactic medium (CGM) of galaxies. We perform 3D magnetohydrohynamics (MHD) simulations with non-equilibrium (NEI) and photoionization modelling, with an eye towards testing simple analytic models. Even purely hydrodynamic collisional ionization equilibrium (CIE) calculations have column densities much lower than observations. Characteristic inflow and turbulent velocities are much less than the shear velocity, and the layer width h∝t^(1/2)_(cool) rather than h ∝ t_(coo)l. Column densities are not independent of density or metallicity as analytic scalings predict, and show surprisingly weak dependence on shear velocity and density contrast. Radiative cooling, rather than Kelvin–Helmholtz instability, appears paramount in determining the saturated state. Low pressure due to fast cooling both seeds turbulence and sets the entrainment rate of hot gas, whose enthalpy flux, along with turbulent dissipation, energizes the layer. Regardless of initial geometry, magnetic fields are amplified and stabilize the mixing layer via magnetic tension, producing almost laminar flow and depressing column densities. NEI effects can boost column densities by factors of a few. Suppression of cooling by NEI or photoionization can, in principle, also increase O VI column densities, but, in practice, is unimportant for CGM conditions. To explain observations, sightlines must pierce hundreds or thousands of mixing layers, which may be plausible if the CGM exists as a ‘fog’ of tiny cloudlets.

Item Type:Article
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URLURL TypeDescription Paper
Ji, Suoqing0000-0001-9658-0588
Additional Information:© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2019 May 2. Received 2019 May 1; in original form 2018 September 23. We thank Max Gronke and Jim Stone for helpful conversations, and the referee Michael Shull for a constructive and helpful report which improved our paper. We acknowledge NASA grants NNX17AK58G and HST-AR-15039.003-A for support. This research has used the Extreme Science and Engineering Discovery Environment (XSEDE allocations TG-AST140086). We have made use of NASA’s Astrophysics Data System and the yt astrophysics analysis software suite (Turk et al. 2010). SPO thanks the law offices of May Oh & Wee for hospitality. PM acknowledges a College of Creative Studies Summer Undergraduate Research Fellowship.
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University of California, Santa BarbaraUNSPECIFIED
Subject Keywords:galaxies: clusters: general, galaxies: evolution, galaxies: haloes, galaxies: magnetic fields
Issue or Number:1
Record Number:CaltechAUTHORS:20190725-125944404
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Official Citation:Suoqing Ji (季索清), S Peng Oh, Phillip Masterson, Simulations of radiative turbulent mixing layers, Monthly Notices of the Royal Astronomical Society, Volume 487, Issue 1, July 2019, Pages 737–754,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:97415
Deposited By: George Porter
Deposited On:25 Jul 2019 21:21
Last Modified:03 Oct 2019 21:31

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