Steady states of the Parker instability

Abstract

We study the linear properties, nonlinear saturation and a steady, strongly nonlinear state of the Parker instability in galaxies. We consider magnetic buoyancy and its consequences with and without cosmic rays. Cosmic rays are described using the fluid approximation with anisotropic, non-Fickian diffusion. To avoid unphysical constraints on the instability (such as boundary conditions often used to specify an unstable background state), nonideal MHD equations are solved for deviations from a background state representing an unstable magnetohydrostatic equilibrium. We consider isothermal gas and neglect rotation. The linear evolution of the instability is in broad agreement with earlier analytical and numerical models; but we show that most of the simplifying assumptions of the earlier work do not hold, such that they provide only a qualitative rather than quantitative picture. In its nonlinear stage the instability has significantly altered the background state from its initial state. Vertical distributions of both magnetic field and cosmic rays are much wider, the gas layer is thinner, and the energy densities of both magnetic field and cosmic rays are much reduced. The spatial structure of the nonlinear state differs from that of any linear modes. A transient gas outflow is driven by the weakly nonlinear instability as it approaches saturation.

References in corpus (17)

• The Pencil Code, a modular MPI code for partial differential equations and particles: multipurpose and multiuser-maintained
• Systematic bias in interstellar magnetic field estimates
• Quantifying Supernovae-Driven Multiphase Galactic Outflows
• The Effect of Cosmic Ray Diffusion on the Parker Instability
• Magnetic fields in the nearby spiral galaxy IC 342: A multi-frequency radio polarization study
• The effect of hyperdiffusivity on turbulent dynamos with helicity
• Dynamo activities driven by magneto-rotational instability and Parker instability in galactic gaseous disk
• Simulating field-aligned diffusion of a cosmic ray gas
• The Parker Instability in Disk Galaxies
• Suppression of small scale dynamo action by an imposed magnetic field
• Three-dimensional Simulations of the Parker Instability in a Uniformly-rotating Disk
• The Role of the Parker Instability in Structuring the Interstellar Medium
• The Parker Instability with Cosmic Ray Streaming
• The Parker Instability under a Linear Gravity
• A numerical approach to the non-uniqueness problem of cosmic ray two-fluid equations at shocks
• Modelling supernova driven turbulence
• The Effect of the Random Magnetic Field Component on the Parker Instability

Cited by in corpus (6)

• Nonlinear magnetic buoyancy instability and turbulent dynamo
• CHANG-ES XXXIV: Magnetic Field Structure in Edge-On Galaxies Characterising large-scale magnetic fields in galactic halos
• The magnetic field of the Radcliffe Wave: starlight polarization at nearest approach to the Sun
• Understanding the radio luminosity function of star-forming galaxies and its cosmological evolution
• Galactic magnetic fields II. Applying the model to nearby galaxies
• Place of the Radcliffe Wave in the Local System