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Virial shocks are suppressed in cosmic ray-dominated galaxy halos

Ji, Suoqing and Kereš, Dušan and Chan, T. K. and Stern, Jonathan and Hummels, Cameron B. and Hopkins, Philip F. and Quataert, Eliot and Faucher-Giguère, Claude-André (2020) Virial shocks are suppressed in cosmic ray-dominated galaxy halos. . (Unpublished)

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We study the impact of cosmic rays (CRs) on the structure of virial shocks, using a large suite of high-resolution cosmological FIRE-2 simulations accounting for CR injection by supernovae. In massive (M_(halo) ≳ 10¹¹ M_⊙), low-redshift (z ≲ 1−2) halos, which are expected to form "hot halos" with slowly-cooling gas in quasi-hydrostatic equilibrium (with a stable virial shock), our simulations without CRs do exhibit clear virial shocks. The cooler phase condensing out from inflows becomes pressure-confined to over-dense clumps, embedded in low-density, volume-filling hot gas whose cooling time is much longer than inflow time. The gas thus transitions sharply from cool free-falling inflow, to hot and thermal-pressure supported at approximately the virial radius (≈R_(vir)), and the shock is quasi-spherical. With CRs, we previously argued that halos in this particular mass and redshift range build up CR-pressure-dominated gaseous halos. Here, we show that when CR pressure dominates over thermal pressure, there is no significant virial shock. Instead, inflowing gas is gradually decelerated by the CR pressure gradient and the gas is relatively subsonic out to and even beyond R_(vir). Rapid cooling also maintains sub-virial temperatures in the inflowing gas within ∼R_(vir).

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper ItemGIZMO code
http://fire.northwestern.eduRelated ItemAdditional Data
Ji, Suoqing0000-0001-9658-0588
Kereš, Dušan0000-0002-1666-7067
Chan, T. K.0000-0003-2544-054X
Stern, Jonathan0000-0002-7541-9565
Hummels, Cameron B.0000-0002-3817-8133
Hopkins, Philip F.0000-0003-3729-1684
Quataert, Eliot0000-0001-9185-5044
Faucher-Giguère, Claude-André0000-0002-4900-6628
Additional Information:SJ is supported by a Sherman Fairchild Fellowship from Caltech. TKC is supported by Science and Technology Facilities Council (STFC) astronomy consolidated grant ST/T000244/1. 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-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. Numerical calculations were run on the Caltech compute cluster “Wheeler”, allocations from XSEDE TG-AST120025, TG-AST130039 and PRAC NSF.1713353 supported by the NSF, and NASA HEC SMD-16-7592. The data used in this work here were, in part, hosted on facilities supported by the Scientific Computing Core at the Flatiron Institute, a division of the Simons Foundation. 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 et al. 2011), SciPy (Oliphant 2007), Matplotlib (Hunter 2007), and the yt astrophysics analysis software suite (Turk et al. 2010), as well as the spectral simulation code CLOUDY (Ferland et al. 2017). 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 Additional data including simulation snapshots, initial conditions, and derived data products are available at
Group:TAPIR, Astronomy Department
Funding AgencyGrant Number
Sherman Fairchild FoundationUNSPECIFIED
Science and Technology Facilities Council (STFC)ST/T000244/1
Alfred P. Sloan FoundationUNSPECIFIED
Cottrell Scholar of Research CorporationUNSPECIFIED
Flatiron InstituteUNSPECIFIED
Simons FoundationUNSPECIFIED
Subject Keywords:galaxies: formation— galaxies: evolution— galaxies: active — stars: formation — cosmology: theory
Record Number:CaltechAUTHORS:20210106-102315985
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107339
Deposited By: George Porter
Deposited On:06 Jan 2021 23:31
Last Modified:06 Jan 2021 23:31

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