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The impact of cosmic rays on dynamical balance and disc–halo interaction in L⋆ disc galaxies

Chan, TK; Kereš, Dušan; Gurvich, Alexander B; Hopkins, Philip F; Trapp, Cameron; Ji, Suoqing; Faucher-Giguère, Claude-André

The impact of cosmic rays on dynamical balance and disc–halo interaction in L⋆ disc galaxies Thumbnail


Authors

Dušan Kereš

Alexander B Gurvich

Philip F Hopkins

Cameron Trapp

Suoqing Ji

Claude-André Faucher-Giguère



Abstract

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 L galaxies 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 (1 kpc scale) 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 L galaxies: 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.

Citation

Chan, T., Kereš, D., Gurvich, A. B., Hopkins, P. F., Trapp, C., Ji, S., & Faucher-Giguère, C. (2022). The impact of cosmic rays on dynamical balance and disc–halo interaction in L⋆ disc galaxies. Monthly Notices of the Royal Astronomical Society, 517(1), 597-615. https://doi.org/10.1093/mnras/stac2236

Journal Article Type Article
Acceptance Date Aug 2, 2022
Online Publication Date Aug 19, 2022
Publication Date 2022
Deposit Date Nov 21, 2022
Publicly Available Date Mar 28, 2024
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 517
Issue 1
Pages 597-615
DOI https://doi.org/10.1093/mnras/stac2236

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