Abstract
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 haloes hosting star-forming (SF) galaxies. Our CR treatment includes injection by supernovae, anisotropic streaming and diffusion along magnetic field lines, and collisional and streaming losses, with constant parallel diffusivity K∼3X 1029 cm2 s_1 chosen to match y-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 haloes at z < 1-2. The gas in these 'CR-dominated' haloes 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 photoionization, with O VI columns >1014'5 cmT2 at distances >150 kpc. CR and thermal gas pressure are locally anticorrelated, 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 haloes are primarily warm/hot (T > 105K) with thermal pressure balancing gravity, collisional ionization dominates, OVI 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.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 4221-4238 |
| Number of pages | 18 |
| Journal | Monthly Notices of the Royal Astronomical Society |
| Volume | 496 |
| Issue number | 4 |
| DOIs | |
| State | Published - Aug 1 2020 |
Funding
We thank the anonymous referee for a constructive and insightful report which improved our paper. 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 coauthors was provided by an Alfred P. Sloan Research Fellowship, NSF Collaborative Research grant #1715847 and CAREER grant #1455342, and NASA grants NNX15AT06G, JPL 1589742, and 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 were 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, Colbert & Varoquaux 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), as well as the spectral simulation code CLOUDY (Ferland et al. 2017).
Keywords
- Cosmology: theory
- Galaxies: active
- Galaxies: evolution
- Galaxies: formation
- Stars: formation
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science