The Parker Instability in Disk Galaxies

Rodrigues, Luiz Felippe S.; Sarson, Graeme R.; Shukurov, Anvar; Bushby, P. J.; Fletcher, Andrew

doi:10.3847/0004-637x/816/1/2

Cited by 38 publications

(57 citation statements)

References 24 publications

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“…This equipartition could be the result of a self-regulated feedback process: provided that CR and magnetic midplane pressures are supercritical, their buoyancy force overcomes the magnetic tension of the dominant toroidal magnetic field, causing it to bend and open up (Parker 1966;Rodrigues et al 2016). CRs stream and diffuse ahead of the gas into the halo along these open field lines and build E-mail: tthomas@aip.de (TT), cpfrommer@aip.de (CP) up a pressure gradient.…”

Section: Introductionmentioning

confidence: 99%

Cosmic-ray hydrodynamics: Alfvén-wave regulated transport of cosmic rays

Thomas

Pfrommer

2019

Monthly Notices of the Royal Astronomical Society

109

128

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Star formation in galaxies appears to be self-regulated by energetic feedback processes. Among the most promising agents of feedback are cosmic rays (CRs), the relativistic ion population of interstellar and intergalactic plasmas. In these environments, energetic CRs are virtually collisionless and interact via collective phenomena mediated by kinetic-scale plasma waves and large-scale magnetic fields. The enormous separation of kinetic and global astrophysical scales requires a hydrodynamic description. Here, we develop a new macroscopic theory for CR transport in the self-confinement picture, which includes CR diffusion and streaming. The interaction between CRs and electromagnetic fields of Alfvénic turbulence provides the main source of CR scattering, and causes CRs to stream along the magnetic field with the Alfvén velocity if resonant waves are sufficiently energetic. However, numerical simulations struggle to capture this effect with current transport formalisms and adopt regularization schemes to ensure numerical stability. We extent the theory by deriving an equation for the CR momentum density along the mean magnetic field and include a transport equation for the Alfvén-wave energy. We account for energy exchange of CRs and Alfvén waves via the gyroresonant instability and include other wave damping mechanisms. Using numerical simulations we demonstrate that our new theory enables stable, self-regulated CR transport. The theory is coupled to magneto-hydrodynamics, conserves the total energy and momentum, and correctly recovers previous macroscopic CR transport formalisms in the steady-state flux limit. Because it is free of tunable parameters, it holds the promise to provide predictable simulations of CR feedback in galaxy formation.1 The Legendre polynomials are eigenfunctions of the pitch-angle Laplace operator ∂ t f | scatt = ∂ µ [ν(1 − µ 2 )/2 ∂ µ f ]. This operator describes pitch-angle diffusion and ν denotes the scattering frequency. Note that this simple Laplacian resembles the actual scattering operator as discussed in equation (51).

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Section: Introductionmentioning

confidence: 99%

Cosmic-ray hydrodynamics: Alfvén-wave regulated transport of cosmic rays

Thomas

Pfrommer

2019

Monthly Notices of the Royal Astronomical Society

109

128

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“…Polarized radio observations of edge-on galaxies show poloidal field lines at the disk-halo interface (e.g., Tüllmann et al 2000). This argues for a dynamical mechanism that is responsible for reorienting the toroidal magnetic field in the disk and may be explained by a CR-driven Parker instability (Rodrigues et al 2016). Indeed, recent hydrodynamical simulations of the formation and evolution of disk galaxies have shown that CR pressure can drive strong bipolar outflows in disk galaxies provided they are allowed to stream (Uhlig et al 2012;Ruszkowski et al 2016) or diffuse (Booth et al 2013; relative to the rest frame of the gas.…”

Section: Introductionmentioning

confidence: 99%

Galactic Winds Driven by Isotropic and Anisotropic Cosmic-Ray Diffusion in Disk Galaxies

Pakmor

Pfrommer

Simpson

et al. 2016

ApJL

189

173

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The physics of cosmic rays (CRs) is a promising candidate for explaining the driving of galactic winds and outflows. Recent galaxy formation simulations have demonstrated the need for active CR transport either in the form of diffusion or streaming to successfully launch winds in galaxies. However, due to computational limitations, most previous simulations have modeled CR transport isotropically. Here, we discuss high-resolution simulations of isolated disk galaxies in a 1011 M e halo with the moving-mesh code AREPO that include injection of CRs from supernovae, advective transport, CR cooling, and CR transport through isotropic or anisotropic diffusion. We show that either mode of diffusion leads to the formation of strong bipolar outflows. However, they develop significantly later in the simulation with anisotropic diffusion compared to the simulation with isotropic diffusion. Moreover, we find that isotropic diffusion allows most of the CRs to quickly diffuse out of the disk, while in the simulation with anisotropic diffusion, most CRs remain in the disk once the magnetic field becomes dominated by its azimuthal component, which occurs after ∼300 Myr. This has important consequences for the gas dynamics in the disk. In particular, we show that isotropic diffusion strongly suppresses the amplification of the magnetic field in the disk compared to anisotropic or no diffusion models. We therefore conclude that reliable simulations which include CR transport inevitably need to account for anisotropic diffusion.

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“…Our stability analysis is a variant of the magnetic buoyancy instability in which magnetic field lines and the direction of the perturbations are in parallel. Importance of the magnetic buoyancy instability in the Galactic disc (including cosmic ray component) to explain formation of the molecular clouds has been emphasized by Parker (1966) and further developments towards understanding nonlinear evolution of this instability are based on the direct numerical simulations (e.g., Matsumoto et al 1993;Basu et al 1997;Hanasz & Lesch 2003;Rodrigues et al 2016). However, we did not explore magnetic buoyancy instability in the presence of a radiation field when the perturbations are perpendicular to the magnetic field vector.…”

Section: Astrophysical Implications: Radiative Bubbles In the Massivementioning

confidence: 99%

Magnetic Rayleigh–Taylor instability in radiative flows

Yaghoobi

Shadmehri

2018

Monthly Notices of the Royal Astronomical Society

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We present a linear analysis of the radiative Rayleigh-Taylor (RT) instability in the presence of magnetic field for both optically thin and thick regimes. When the flow is optically thin, magnetic field not only stabilizes perturbations with short wavelengths, but also growth rate of the instability at long wavelengths is reduced compared to a nonmagnetized case. Then, we extend our analysis to the optically thick flows with a conserved total specific entropy and properties of the unstable perturbations are investigated in detail. Growth rate of the instability at short wavelengths is suppressed due to the presence of the magnetic field, however, growth rate is nearly constant at long wavelengths because of the radiation field. Since the radiative bubbles around massive protostars are subject to the RT instability, we also explore implications of our results in this context. In the nonmagnetized case, the growth time-scale of the instability for a typical bubble is found less than one thousand years which is very short compared to the typical star formation time-scale. Magnetic field with a reasonable strength significantly increases the growth time-scale to more than hundreds of thousands years. The instability, furthermore, is more efficient at large wavelengths, whereas in the non-magnetized case, growth rate at short wavelengths is more significant.

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The Parker Instability in Disk Galaxies

Cited by 38 publications

References 24 publications

Cosmic-ray hydrodynamics: Alfvén-wave regulated transport of cosmic rays

Cosmic-ray hydrodynamics: Alfvén-wave regulated transport of cosmic rays

Galactic Winds Driven by Isotropic and Anisotropic Cosmic-Ray Diffusion in Disk Galaxies

Magnetic Rayleigh–Taylor instability in radiative flows

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