Structures in a class of magnetized scale-free discs

Yue Shen, Xin Liu, Yu Qing Lou

Research output: Contribution to journalArticle

Abstract

We construct analytically stationary global configurations for both aligned and logarithmic spiral coplanar magnetohydrodynamics (MHD) perturbations in an axisymmetric background MHD disc with a power-law surface mass density ∑0 α r, a coplanar azimuthal magnetic field B0 α r, a consistent self-gravity and a power-law rotation curve ν0 α r, where ν0 is the linear azimuthal gas rotation speed. The barotropic equation of state Π α ∑n is adopted for both MHD background equilibrium and coplanar MHD perturbations where Π is the vertically integrated pressure and n is the barotropic index. For a scale-free background MHD equilibrium, a relation exists among α, β, γ and n such that only one parameter (e.g. β) is independent. For a linear axisymmetric stability analysis, we provide global criteria in various parameter regimes. For non-axisymmetric aligned and logarithmic spiral cases, two branches of perturbation modes (i.e. fast and slow MHD density waves) can be derived once β is specified. To complement the magnetized singular isothermal disc analysis of Lou, we extend the analysis to a wider range of -1/ 4 < β< 1/2. As an illustrative example, we discuss specifically the β= 1/4 case when the background magnetic field is force-free. Angular momentum conservation for coplanar MHD perturbations and other relevant aspects of our approach are discussed.

Original languageEnglish (US)
Pages (from-to)1333-1356
Number of pages24
JournalMonthly Notices of the Royal Astronomical Society
Volume356
Issue number4
DOIs
StatePublished - Feb 1 2005
Externally publishedYes

Keywords

  • Galaxies: Kinematics and dynamics
  • Galaxies: Spiral
  • Galaxies: Structure
  • Ism: Magnetic fields
  • MHD
  • Stars: Formation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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