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Effects of Different Cosmic Ray Transport Models on Galaxy Formation

Hopkins, Philip F. and Chan, T. K. and Squire, Jonathan and Quataert, Eliot and Ji, Suoqing and Kereš, Dušan and Faucher-Giguère, Claude-André (2020) Effects of Different Cosmic Ray Transport Models on Galaxy Formation. . (Unpublished)

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Cosmic rays (CRs) with ~GeV energies can contribute significantly to the energy and pressure budget in the interstellar, circumgalactic, and intergalactic medium (ISM, CGM, IGM). Recent cosmological simulations have begun to explore these effects, but almost all studies have been restricted to simplified models with constant CR diffusivity and/or streaming speeds. Physical models of CR propagation/scattering via extrinsic turbulence and self-excited waves predict transport coefficients which are complicated functions of local plasma properties. In a companion paper, we consider a wide range of observational constraints to identify proposed physically-motivated cosmic-ray propagation scalings which satisfy both detailed Milky Way (MW) and extra-galactic γ-ray constraints. Here, we compare the effects of these models relative to simpler 'diffusion+streaming' models on galaxy and CGM properties at dwarf through MW mass scales. The physical models predict large local variations in CR diffusivity, with median diffusivity increasing with galacto-centric radii and decreasing with galaxy mass and redshift. These effects lead to a more rapid dropoff of CR energy density in the CGM (compared to simpler models), in turn producing weaker effects of CRs on galaxy star formation rates (SFRs), CGM absorption profiles and galactic outflows. The predictions of the more physical CR models tend to lie 'in between' models which ignore CRs entirely and models which treat CRs with constant diffusivity.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Hopkins, Philip F.0000-0003-3729-1684
Chan, T. K.0000-0003-2544-054X
Squire, Jonathan0000-0001-8479-962X
Quataert, Eliot0000-0001-9185-5044
Ji, Suoqing0000-0001-9658-0588
Kereš, Dušan0000-0002-1666-7067
Faucher-Giguère, Claude-André0000-0002-4900-6628
Additional Information:Support for PFH was provided by NSF Collaborative Research Grants 1715847 & 1911233, NSF CAREER grant 1455342, and NASA grants 80NSSC18K0562 and JPL 1589742. CAFG was supported by NSF 1517491, 1715216, and CAREER 1652522; NASA 17-ATP17-0067; and by a Cottrell Scholar Award. Support for JS was provided by Rutherford Discovery Fellowship RDF-U001804 and Marsden Fund grant UOO1727 from the Royal Society Te Apārangi. 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.
Group:Astronomy Department, TAPIR
Funding AgencyGrant Number
Cottrell Scholar of Research CorporationUNSPECIFIED
Royal Society Te ApārangiRDF-U001804
Royal Society Te ApārangiUOO1727
Subject Keywords:cosmic rays—plasmas—galaxies: formation—galaxies: evolution—galaxies: active—stars: formation
Record Number:CaltechAUTHORS:20200626-150130701
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104103
Deposited By: George Porter
Deposited On:29 Jun 2020 14:03
Last Modified:29 Jun 2020 14:03

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