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Cosmic ray feedback in the FIRE simulations: constraining cosmic ray propagation with GeV gamma ray emission
Abstract We present the implementation and the first results of cosmic ray (CR) feedback in the Feedback In Realistic Environments (FIRE) simulations. We investigate CR feedback in non-cosmological simulations of dwarf, sub-L⋆ starburst, and L⋆ galaxies with different propagation models, including advection, isotropic and anisotropic diffusion, and streaming along field lines with different transport coefficients. We simulate CR diffusion and streaming simultaneously in galaxies with high resolution, using a two moment method. We forward-model and compare to observations of γ-ray emission from nearby and starburst galaxies. We reproduce the γ-ray observations of dwarf and L⋆ galaxies with constant isotropic diffusion coefficient κ ∼ 3 × 1029 cm2 s−1. Advection-only and streaming-only models produce order-of-magnitude too large γ-ray luminosities in dwarf and L⋆ galaxies. We show that in models that match the γ-ray observations, most CRs escape low-gas-density galaxies (e.g. dwarfs) before significant collisional losses, while starburst galaxies are CR proton calorimeters. While adiabatic losses can be significant, they occur only after CRs escape galaxies, so they are only of secondary importance for γ-ray emissivities. Models where CRs are “trapped” in the star-forming disk have lower star formation efficiency, but these models are ruled out by γ-ray observations. For models with constant κ more »
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NSF-PAR ID:
10105535
Journal Name:
Monthly Notices of the Royal Astronomical Society
ISSN:
0035-8711
Sponsoring Org:
National Science Foundation
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5. (Ed.)
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