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Numerical study of cosmic ray confinement through dust resonant drag instabilities

Ji, Suoqing and Squire, Jonathan and Hopkins, Philip F. (2022) Numerical study of cosmic ray confinement through dust resonant drag instabilities. Monthly Notices of the Royal Astronomical Society, 513 (1). pp. 282-295. ISSN 0035-8711. doi:10.1093/mnras/stac895.

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We investigate the possibility of cosmic ray (CR) confinement by charged dust grains through resonant drag instabilities (RDIs). We perform magnetohydrodynamic particle-in-cell simulations of magnetized gas mixed with charged dust and cosmic rays, with the gyro-radii of dust and GeV CRs on ∼au scales fully resolved. As a first study, we focus on one type of RDI wherein charged grains drift super-Alfvénically, with Lorentz forces strongly dominating over drag forces. Dust grains are unstable to the RDIs and form concentrated columns and sheets, whose scale grows until saturating at the simulation box size. Initially perfectly streaming CRs are strongly scattered by RDI-excited Alfvén waves, with the growth rate of the CR perpendicular velocity components equaling the growth rate of magnetic field perturbations. These rates are well-predicted by analytic linear theory. CRs finally become isotropized and drift at least at ∼v_A by unidirectional Alfvén waves excited by the RDIs, with a uniform distribution of the pitch angle cosine μ and a flat profile of the CR pitch angle diffusion coefficient D_(μμ) around μ = 0, without the ‘90○ pitch angle problem.’ With CR feedback on the gas included, D_(μμ) decreases by a factor of a few, indicating a lower CR scattering rate, because the backreaction on the RDI from the CR pressure adds extra wave damping, leading to lower quasi-steady-state scattering rates. Our study demonstrates that the dust-induced CR confinement can be very important under certain conditions, e.g. the dusty circumgalactic medium around quasars or superluminous galaxies.

Item Type:Article
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URLURL TypeDescription Paper ItemGIZMO code
Ji, Suoqing0000-0001-9658-0588
Squire, Jonathan0000-0001-8479-962X
Hopkins, Philip F.0000-0003-3729-1684
Additional Information:© 2022 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2022 March 29. Received 2022 March 10; in original form 2021 November 29. Published: 13 April 2022. SJ thanks E. Quataert for helpful discussions, and the referee for constructive comments which improve this manuscript. SJ is supported by a Sherman Fairchild Fellowship from Caltech, the Natural Science Foundation of China (grants 12133008, 12192220, and 12192223) and the science research grants from the China Manned Space Project (No. CMS-CSST-2021-B02). Support for JS was provided by Rutherford Discovery Fellowship RDF-U001804 and Marsden Fund grant UOO1727, which are managed through the Royal Society Te Apārangi. Support for PFH was provided by NSF Research Grants 1911233 and 20009234, NSF CAREER grant 1455342, NASA grants 80NSSC18K0562, HST-AR-15800.001-A, JPL 1589742. Numerical calculations were run on the Caltech compute cluster ‘Wheeler,’ allocations FTA-Hopkins/AST20016 supported by the NSF and TACC, and NASA HEC SMD-16-7592. We have made use of NASA’s Astrophysics Data System. Data analysis and visualization are made with PYTHON 3, and its packages including NUMPY (Van Der Walt, Colbert & Varoquaux 2011), SCIPY (Oliphant 2007), MATPLOTLIB(Hunter 2007), and the yt astrophysics analysis software suite (Turk et al. 2010). Data Availability: The data supporting the plots within this article are available on reasonable request to the corresponding author. A public version of the GIZMO code is available at
Group:Astronomy Department, TAPIR
Funding AgencyGrant Number
Sherman Fairchild FoundationUNSPECIFIED
National Natural Science Foundation of China12133008
National Natural Science Foundation of China12192220
National Natural Science Foundation of China12192223
China Manned Space ProjectCMS-CSST-2021-B02
Royal Society Te ApārangiRDF-U001804
Marsden Fund of the Royal Society of New ZealandUOO1727
Subject Keywords:MHD –plasmas –methods: numerical –cosmic rays –ISM: structure –galaxies: active
Issue or Number:1
Record Number:CaltechAUTHORS:20220228-183305395
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Official Citation:Suoqing Ji, Jonathan Squire, Philip F Hopkins, Numerical study of cosmic ray confinement through dust resonant drag instabilities, Monthly Notices of the Royal Astronomical Society, Volume 513, Issue 1, June 2022, Pages 282–295,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113649
Deposited By: George Porter
Deposited On:28 Feb 2022 23:20
Last Modified:06 May 2022 17:59

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