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But What About... Cosmic Rays, Magnetic Fields, Conduction, & Viscosity in Galaxy Formation

Hopkins, Philip F. and Chan, T. K. and Garrison-Kimmel, Shea and Ji, Suoqing and Su, Kung-Yi and Hummels, Cameron B. and Kereš, Dušan and Quataert, Eliot and Faucher-Giguère, Claude-André (2020) But What About... Cosmic Rays, Magnetic Fields, Conduction, & Viscosity in Galaxy Formation. Monthly Notices of the Royal Astronomical Society, 492 (3). pp. 3465-3498. ISSN 0035-8711.

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We present and study a large suite of high-resolution cosmological zoom-in simulations, using the FIRE-2 treatment of mechanical and radiative feedback from massive stars, together with explicit treatment of magnetic fields, anisotropic conduction and viscosity (accounting for saturation and limitation by plasma instabilities at high β), and cosmic rays (CRs) injected in supernovae shocks (including anisotropic diffusion, streaming, adiabatic, hadronic and Coulomb losses). We survey systems from ultrafaint dwarf (⁠M∗∼10⁴M⊙⁠, M_(halo)∼10⁹M⊙⁠) through Milky Way/Local Group (MW/LG) masses, systematically vary uncertain CR parameters (e.g. the diffusion coefficient κ and streaming velocity), and study a broad ensemble of galaxy properties [masses, star formation (SF) histories, mass profiles, phase structure, morphologies, etc.]. We confirm previous conclusions that magnetic fields, conduction, and viscosity on resolved (⁠≳1 pc) scales have only small effects on bulk galaxy properties. CRs have relatively weak effects on all galaxy properties studied in dwarfs (⁠M∗≪10¹⁰M⊙, M_(halo)≲10¹¹M⊙⁠), or at high redshifts (z ≳ 1–2), for any physically reasonable parameters. However, at higher masses (⁠M_(halo)≳10¹¹M⊙) and z ≲ 1–2, CRs can suppress SF and stellar masses by factors ∼2–4, given reasonable injection efficiencies and relatively high effective diffusion coefficients κ≳3×10²⁹cm²s⁻¹⁠. At lower κ, CRs take too long to escape dense star-forming gas and lose their energy to collisional hadronic losses, producing negligible effects on galaxies and violating empirical constraints from spallation and γ-ray emission. At much higher κ CRs escape too efficiently to have appreciable effects even in the CGM. But around κ∼3×10²⁹cm²s⁻¹⁠, CRs escape the galaxy and build up a CR-pressure-dominated halo which maintains approximate virial equilibrium and supports relatively dense, cool (T ≪ 10⁶ K) gas that would otherwise rain on to the galaxy. CR ‘heating’ (from collisional and streaming losses) is never dominant.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Hopkins, Philip F.0000-0003-3729-1684
Chan, T. K.0000-0003-2544-054X
Garrison-Kimmel, Shea0000-0002-4655-8128
Ji, Suoqing0000-0001-9658-0588
Su, Kung-Yi0000-0003-1598-0083
Hummels, Cameron B.0000-0002-3817-8133
Kereš, Dušan0000-0002-1666-7067
Quataert, Eliot0000-0001-9185-5044
Faucher-Giguère, Claude-André0000-0002-4900-6628
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 ( Received: 10 May 2019; Revision received: 07 November 2019; Accepted: 25 November 2019; Published: 05 December 2019. Support for PFH and co-authors was provided by an Alfred P. Sloan Research Fellowship, NSF Collaborative Research Grant #1715847 and CAREER grant#1455342, and NASA grants NNX15AT06G, JPL 1589742, 17-ATP17-0214. DK was supported by NSF grant AST-1715101 and the Cottrell Scholar Award from the Research Corporation for Science Advancement. CAFG was supported by NSF through grants AST-1517491, AST-1715216, and CAREER award AST-1652522, by NASA through grant 17-ATP17-0067, and by a Cottrell Scholar Award from the Research Corporation for Science Advancement. Numerical calculations were run on the Caltech compute cluster ‘Wheeler,’ allocations from XSEDE TG-AST130039 and TG-AST120025 and PRAC NSF.1713353 supported by the NSF, and NASA HEC SMD-16-7592.
Group:Astronomy Department, TAPIR
Funding AgencyGrant Number
Alfred P. Sloan FoundationUNSPECIFIED
Cottrell Scholar of Research CorporationUNSPECIFIED
Subject Keywords:stars: formation, galaxies: active, galaxies: evolution, galaxies: formation, cosmology: theory
Issue or Number:3
Record Number:CaltechAUTHORS:20190729-112957859
Persistent URL:
Official Citation:Philip F Hopkins, T K Chan, Shea Garrison-Kimmel, Suoqing Ji, Kung-Yi Su, Cameron B Hummels, Dušan Kereš, Eliot Quataert, Claude-André Faucher-Giguère, But what about...: cosmic rays, magnetic fields, conduction, and viscosity in galaxy formation, Monthly Notices of the Royal Astronomical Society, Volume 492, Issue 3, March 2020, Pages 3465–3498,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:97488
Deposited By: Tony Diaz
Deposited On:29 Jul 2019 18:38
Last Modified:27 Mar 2020 17:49

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