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Properties of the Circumgalactic Medium in Cosmic Ray-Dominated Galaxy Halos

Ji, Suoqing and Chan, T. K. and Hummels, Cameron B. and Hopkins, Philip F. and Stern, Jonathan and Kereš, Dušan and Quataert, Eliot and Faucher-Giguère, Claude-André and Murray, Norman (2019) Properties of the Circumgalactic Medium in Cosmic Ray-Dominated Galaxy Halos. . (Unpublished)

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We investigate the impact of cosmic rays (CRs) on the circumgalactic medium (CGM) in FIRE-2 simulations, for ultra-faint dwarf through Milky Way (MW)-mass halos hosting star-forming (SF) galaxies. Our CR treatment includes injection by supernovae, anisotropic streaming and diffusion along magnetic field lines, collisional and streaming losses, with constant parallel diffusivity κ∼3×10²⁹ cm² s⁻¹ chosen to match γ-ray observations. With this, CRs become more important at larger halo masses and lower redshifts, and dominate the pressure in the CGM in MW-mass halos at z ≲ 1−2. The gas in these “CR-dominated” halos differs significantly from runs without CRs: the gas is primarily cool (a few ∼10⁴ K), and the cool phase is volume-filling and has a thermal pressure below that needed for virial or local thermal pressure balance. Ionization of the “low” and “mid” ions in this diffuse cool gas is dominated by photo-ionization, with O VI columns ≳10^(14.5) cm⁻² at distances ≳150 kpc. CR and thermal gas pressure are locally anti-correlated, maintaining total pressure balance, and the CGM gas density profile is determined by the balance of CR pressure gradients and gravity. Neglecting CRs, the same halos are primarily warm/hot (T ≳ 10⁵ K) with thermal pressure balancing gravity, collisional ionization dominates, O VI columns are lower and Ne VIII higher, and the cool phase is confined to dense filaments in local thermal pressure equilibrium with the hot phase.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Ji, Suoqing0000-0001-9658-0588
Chan, T. K.0000-0003-2544-054X
Hummels, Cameron B.0000-0002-3817-8133
Hopkins, Philip F.0000-0003-3729-1684
Kereš, Dušan0000-0002-1666-7067
Quataert, Eliot0000-0001-9185-5044
Faucher-Giguère, Claude-André0000-0002-4900-6628
Additional Information:SJ is supported by a Sherman Fairchild Fellowship from Caltech. SJ thanks Joe Burchett, Zheng Cai, Taotao Fang, Peng Oh, J. Xavier Prochaska, Gwen Rudie, Mateusz Ruszkowski, Britton Smith, Daniel Wang and Jessica Werk for many helpful comments and discussions, and the Aspen Center for Physics supported by NSF PHY-1607611 for its hospitality where part of this work was completed. 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, 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. 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), Healpy (Górski et al. 2005; Zonca et al. 2019), the yt astrophysics analysis software suite (Turk et al. 2010) and the absorption spectra tool Trident (Hummels et al. 2017), aswell as the spectral simulation code CLOUDY (Ferland et al. 2017).
Group:Astronomy Department, TAPIR
Funding AgencyGrant Number
Sherman Fairchild FoundationUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
Cottrell Scholar of Research CorporationUNSPECIFIED
Subject Keywords:galaxies: formation — galaxies: evolution — galaxies: active — stars: formation — cosmology: theory
Record Number:CaltechAUTHORS:20200310-145036739
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101837
Deposited By: Tony Diaz
Deposited On:10 Mar 2020 22:03
Last Modified:10 Mar 2020 22:03

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