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Cosmic ray driven outflows to Mpc scales from L* galaxies

Hopkins, Philip F. and Chan, T. K. and Ji, Suoqing and Hummels, Cameron and Kereš, Dušan and Quataert, Eliot and Faucher-Giguère, Claude-André (2021) Cosmic ray driven outflows to Mpc scales from L* galaxies. Monthly Notices of the Royal Astronomical Society, 501 (3). pp. 3640-3662. ISSN 0035-8711. doi:10.1093/mnras/staa3690.

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We study the effects of cosmic rays (CRs) on outflows from star-forming galaxies in the circum and intergalactic medium (CGM/IGM), in high-resolution, fully cosmological FIRE-2 simulations (accounting for mechanical and radiative stellar feedback, magnetic fields, anisotropic conduction/viscosity/CR diffusion and streaming, and CR losses). We showed previously that massive (⁠M_(halo)≳10¹¹), low-redshift (z ≲ 1–2) haloes can have CR pressure dominate over thermal CGM pressure and balance gravity, giving rise to a cooler CGM with an equilibrium density profile. This dramatically alters outflows. Absent CRs, high gas thermal pressure in massive haloes ‘traps’ galactic outflows near the disc, so they recycle. With CRs injected in supernovae as modelled here, the low-pressure halo allows ‘escape’ and CR pressure gradients continuously accelerate this material well into the IGM in ‘fast’ outflows, while lower-density gas at large radii is accelerated in situ into ‘slow’ outflows that extend to >Mpc scales. CGM/IGM outflow morphologies are radically altered: they become mostly volume-filling (with inflow in a thin mid-plane layer) and coherently biconical from the disc to >Mpc. The CR-driven outflows are primarily cool (⁠T∼10⁵) and low velocity. All of these effects weaken and eventually vanish at lower halo masses (⁠≲10¹¹M⊙⁠) or higher redshifts (z ≳ 1–2), reflecting the ratio of CR to thermal + gravitational pressure in the outer halo. We present a simple analytical model that explains all of the above phenomena. We caution that these predictions may depend on uncertain CR transport physics.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper ItemGIZMO Code
http://fire.northwestern.eduRelated ItemAdditional Data
Hopkins, Philip F.0000-0003-3729-1684
Chan, T. K.0000-0003-2544-054X
Ji, Suoqing0000-0001-9658-0588
Hummels, Cameron0000-0002-3817-8133
Kereš, Dušan0000-0002-1666-7067
Quataert, Eliot0000-0001-9185-5044
Faucher-Giguère, Claude-André0000-0002-4900-6628
Additional Information:© 2020 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 2020 November 5. Received 2020 November 4; in original form 2020 February 6. Published: 28 November 2020. 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, and17-ATP17-0214. CAFG was supported by NSF through grants AST-1517491, AST-1715216, and CAREER award AST-1652522, by NASA through grant 17-ATP17-0067, by STScI through grants HST-GO-14681.011,HST-GO-14268.022-A, and HST-AR-14293.001-A, and by a Cottrell Scholar Award from the Research Corporation for Science Advancement. DK was supported by NSF grant AST-1715101 and the Cottrell Scholar Award from the Research Corporation for Science Advancement. Numerical calculations were run on the Caltech compute cluster ‘Wheeler,’ allocations FTA-Hopkins supported by the NSF and TACC, and NASA HEC SMD-16-7592. Data Availability Statement: 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 Additional data including simulation snapshots, initial conditions, and derived data products are available at
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 – galaxies: intergalactic medium – cosmology: theory
Issue or Number:3
Record Number:CaltechAUTHORS:20200310-082303427
Persistent URL:
Official Citation:Philip F Hopkins, T K Chan, Suoqing Ji, Cameron B Hummels, Dušan Kereš, Eliot Quataert, Claude-André Faucher-Giguère, Cosmic ray driven outflows to Mpc scales from L* galaxies, Monthly Notices of the Royal Astronomical Society, Volume 501, Issue 3, March 2021, Pages 3640–3662,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101810
Deposited By: Tony Diaz
Deposited On:10 Mar 2020 16:10
Last Modified:31 Mar 2021 22:28

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