Cosmic-Ray Transport in Simulations of Star-forming Galactic Disks

Abstract

Cosmic ray transport on galactic scales depends on the detailed properties of the magnetized, multiphase interstellar medium (ISM). In this work, we post-process a high-resolution TIGRESS magnetohydrodynamic simulation modeling a local galactic disk patch with a two-moment fluid algorithm for cosmic ray transport. We consider a variety of prescriptions for the cosmic rays, from a simple purely diffusive formalism with constant scattering coefficient, to a physically-motivated model in which the scattering coefficient is set by critical balance between streaming-driven Alfvén wave excitation and damping mediated by local gas properties. We separately focus on cosmic rays with kinetic energies of $\sim 1$ GeV (high-energy) and $\sim 30$~MeV (low-energy), respectively important for ISM dynamics and chemistry. We find that simultaneously accounting for advection, streaming, and diffusion of cosmic rays is crucial for properly modeling their transport. Advection dominates in the high-velocity, low-density, hot phase, while diffusion and streaming are more important in higher density, cooler phases. Our physically-motivated model shows that there is no single diffusivity for cosmic-ray transport: the scattering coefficient varies by four or more orders of magnitude, maximal at density $n_{\mathrm{H}}\sim 0.01{\mathrm{cm}}^{-3}$. Ion-neutral damping of Alfvén waves results in strong diffusion and nearly uniform cosmic ray pressure within most of the mass of the ISM. However, cosmic rays are trapped near the disk midplane by the higher scattering rate in the surrounding lower-density, higher-ionization gas. The transport of high-energy cosmic rays differs from that of low-energy cosmic rays, with less effective diffusion and greater energy losses for the latter.

arXiv commentAccepted for publication in ApJ

References in corpus (62)

• On the variation of the Initial Mass Function
• Starburst99: Synthesis Models for Galaxies with Active Star Formation
• Cosmic-ray propagation and interactions in the Galaxy
• FIRE-2 Simulations: Physics versus Numerics in Galaxy Formation
• Athena: A New Code for Astrophysical MHD
• The Athena++ Adaptive Mesh Refinement Framework: Design and Magnetohydrodynamic Solvers
• Revised equipartition & minimum energy formula for magnetic field strength estimates from radio synchrotron observations
• Regulation of Star Formation Rates in Multiphase Galactic Disks: a Thermal/Dynamical Equilibrium Model
• Investigating the Cosmic-Ray Ionization Rate in the Galactic Diffuse Interstellar Medium through Observations of H3+
• Galactic and extragalactic magnetic fields
• Maximally Star-Forming Galactic Disks I. Starburst Regulation Via Feedback-Driven Turbulence
• Constraints on cosmic-ray propagation models from a global Bayesian analysis
• Scattering of Cosmic Rays by Magnetohydrodynamic Interstellar Turbulence
• The Milky Way's Kiloparsec Scale Wind: A Hybrid Cosmic-Ray and Thermally Driven Outflow
• Strong evidences of hadron acceleration in Tycho's Supernova Remnant
• Herschel Survey of Galactic OH+, H2O+, and H3O+: Probing the Molecular Hydrogen Fraction and Cosmic-Ray Ionization Rate
• Spectral breaks as a signature of cosmic ray induced turbulence in the Galaxy
• Three-phase Interstellar medium in Galaxies Resolving Evolution with Star formation and Supernova feedback (TIGRESS): Algorithms, Fiducial model, and Convergence
• The SILCC project: III. Regulation of star formation and outflows by stellar winds and supernovae
• Fermi Establishes Classical Novae as a Distinct Class of Gamma-Ray Sources
• Three Dimensional Hydrodynamic Simulations of Multiphase Galactic Disks with Star Formation Feedback: I. Regulation of Star Formation Rates
• Launching cosmic-ray-driven outflows from the magnetized interstellar medium
• Numerical Simulations of Multiphase Winds and Fountains from Star-Forming Galactic Disks: I. Solar Neighborhood TIGRESS Model
• Cosmic-ray ionisation in circumstellar discs
• Wave damping by MHD turbulence and its effect upon cosmic ray propagation in the ISM
• Global simulations of galactic winds including cosmic ray streaming
• Cosmic Ray Transport in the Galaxy: a Review
• Bayesian analysis of cosmic-ray propagation: evidence against homogeneous diffusion
• Cosmic ray feedback in the FIRE simulations: constraining cosmic ray propagation with GeV gamma ray emission
• The cosmic ray ionization rate in the Galactic disk, as determined from observations of molecular ions
• Implementation of the Shearing Box Approximation in Athena
• Cooler and smoother -- the impact of cosmic rays on the phase structure of galactic outflows
• The role of cosmic ray pressure in accelerating galactic outflows
• Impact of Cosmic Ray Transport on Galactic Winds
• First results from SMAUG: Characterization of Multiphase Galactic Outflows from a Suite of Local Star-Forming Galactic Disk Simulations
• Cosmic rays can drive strong outflows from gas-rich high-redshift disk galaxies
• Impact of low-energy cosmic rays on star formation
• Vertical Equilibrium, Energetics, and Star Formation Rates in Magnetized Galactic Disks Regulated by Momentum Feedback from Supernovae
• A Two-moment Radiation Hydrodynamics Module in Athena Using a Time-explicit Godunov Method
• Testing Physical Models for Cosmic Ray Transport Coefficients on Galactic Scales: Self-Confinement and Extrinsic Turbulence at GeV Energies
• Origin of the Cosmic Ray Galactic Halo Driven by Advected Turbulence and Self-Generated Waves
• A New Numerical Scheme for Cosmic Ray Transport
• Cosmic ray transport in starburst galaxies
• Time-dependent galactic winds I. Structure and evolution of galactic outflows accompanied by cosmic ray acceleration
• Spatial-Dependent Diffusion of Cosmic Rays and the Ratio of pbar/p, B/C
• Damping of Alfven waves by Turbulence and its Consequences: from Cosmic-Rays Streaming to Launching Winds
• Galactic cosmic-ray propagation in the light of AMS-02: I. Analysis of protons, helium, and antiprotons
• Galactic disk winds driven by cosmic ray pressure
• Local Simulations of Spiral Galaxies with the TIGRESS Framework: I. Star Formation and Arm Spurs/Feathers
• Magnetohydrodynamic-Particle-in-Cell Simulations of the Cosmic-Ray Streaming Instability: Linear Growth and Quasi-linear Evolution
• Role of Cosmic Ray Streaming and Turbulent Damping in Driving Galactic Winds
• Equipartition and Cosmic Ray Energy Densities in Central Molecular Zones of Starbursts
• Diffusive Versus Free-Streaming Cosmic Ray Transport in Molecular Clouds
• Cosmic rays and non-thermal emission in simulated galaxies. I. Electron and proton spectra compared to Voyager-1 data
• An observational test for correlations between cosmic rays and magnetic fields
• Kinematics and Dynamics of Multiphase Outflows in Simulations of the Star-Forming Galactic ISM
• Simulations of cosmic ray propagation
• The EDIBLES survey IV. Cosmic ray ionization rates in diffuse clouds from near-ultraviolet observations of interstellar OH${}^{+}$
• Cosmic rays across the star-forming galaxy sequence. I: Cosmic ray pressures and calorimetry
• High $\beta$ Effects on Cosmic Ray Streaming in Galaxy Clusters
• Heuristic Description of Perpendicular Diffusion of Energetic Particles in Astrophysical Plasmas
• Influence of Ion-Neutral Damping on the Cosmic-Ray Streaming Instability: Magnetohydrodynamic Particle-in-cell Simulations

Cited by in corpus (4)

• Introducing TIGRESS-NCR: I. Co-Regulation of the Multiphase Interstellar Medium and Star Formation Rates
• Standard Self-Confinement and Extrinsic Turbulence Models for Cosmic Ray Transport are Fundamentally Incompatible with Observations
• Photochemistry and Heating/Cooling of the Multiphase Interstellar Medium with UV Radiative Transfer for Magnetohydrodynamic Simulations
• The impact of cosmic rays on dynamical balance and disk-halo interaction in Lstar disk galaxies