Journal Article

Equilibrium initialization and stability of three-dimensional gas discs

Hsiang-Hsu Wang, Ralf S. Klessen, Cornelis P. Dullemond, Frank C. van den Bosch and Burkhard Fuchs

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 407, issue 2, pages 705-720
Published in print September 2010 | ISSN: 0035-8711
Published online September 2010 | e-ISSN: 1365-2966 | DOI:
Equilibrium initialization and stability of three-dimensional gas discs

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We present a new systematic way of setting up galactic gas discs based on the assumption of detailed hydrodynamic equilibrium. To do this, we need to specify the density distribution and the velocity field which supports the disc. We first show that the required circular velocity has no dependence on the height above or below the mid-plane so long as the gas pressure is a function of density only. The assumption of discs being very thin enables us to decouple the vertical structure from the radial direction. Based on that, the equation of hydrostatic equilibrium together with the reduced Poisson equation leads to two sets of second-order non-linear differential equations, which are easily integrated to set up a stable disc. We call one approach ‘density method’ and the other one ‘potential method’. Gas discs in detailed balance are especially suitable for investigating the onset of the gravitational instability. We revisit the question of global, axisymmetric instability using fully three-dimensional disc simulations. The impact of disc thickness on the disc instability and the formation of spontaneously induced spirals is studied systematically with or without the presence of the stellar potential. In our models, the numerical results show that the threshold value for disc instability is shifted from unity to 0.69 for self-gravitating thick discs and to 0.75 for combined stellar and gas thick discs. The simulations also show that self-induced spirals occur in the correct regions and with the right numbers as predicted by the analytic theory.

Keywords: methods: numerical; galaxies: evolution; galaxies: structure

Journal Article.  10793 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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