The impact of cosmic rays on dynamical balance and disc-halo interaction in Ldisc galaxies

T. K. Chan*, Dušan Kereš, Alexander B. Gurvich, Philip F. Hopkins, Cameron Trapp, Suoqing Ji, Claude Andre Faucher-Giguère

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Cosmic rays (CRs) are an important component in the interstellar medium, but their effect on the dynamics of the disc-halo interface (<10 kpc from the disc) is still unclear. We study the influence of CRs on the gas above the disc with high-resolution FIRE-2 cosmological simulations of late-type Lgalaxies at redshift z ∼0. We compare runs with and without CR feedback (with constant anisotropic diffusion κ ∼3 × 1029 cm2 s-1 and streaming). Our simulations capture the relevant disc-halo interactions, including outflows, inflows, and galactic fountains. Extra-planar gas in all of the runs satisfies dynamical balance, where total pressure balances the weight of the overlying gas. While the kinetic pressure from non-uniform motion dominates in the mid-plane, thermal and bulk pressures (or CR pressure if included) take over at large heights. We find that with CR feedback, (1) the warm (∼104 K) gas is slowly accelerated by CRs; (2) the hot (>5 × 105 K) gas scale height is suppressed; (3) the warm-hot (2 × 104-5 × 105 K) medium becomes the most volume-filling phase in the disc-halo interface. We develop a novel conceptual model of the near-disc gas dynamics in low-redshift Lgalaxies: with CRs, the disc-halo interface is filled with CR-driven warm winds and hot superbubbles that are propagating into the circumgalactic medium with a small fraction falling back to the disc. Without CRs, most outflows from hot superbubbles are trapped by the existing hot halo and gravity, so typically they form galactic fountains.

Original languageEnglish (US)
Pages (from-to)597-615
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - Nov 1 2022


  • galaxies: kinematics and dynamics
  • galaxies: spiral
  • ISM: cosmic rays
  • ISM: kinematics and dynamics

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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