Journal Article

The effective stability parameter for two-component galactic discs: is <i>Q</i><sup>−1</sup>≈<i>Q</i><sup>−1</sup><sub>stars</sub>+<i>Q</i><sup>−1</sup><sub>gas</sub>?

Alessandro B. Romeo and Joachim Wiegert

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 416, issue 2, pages 1191-1196
Published in print September 2011 | ISSN: 0035-8711
Published online September 2011 | e-ISSN: 1365-2966 | DOI:
The effective stability parameter for two-component galactic discs: is Q−1≈Q−1stars+Q−1gas?

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The Wang–Silk approximation, Q−1Q−1stars+Q−1gas, is frequently used for estimating the effective Q parameter in two-component discs of stars and gas. Here we analyse this approximation in detail, and show how its accuracy depends on the radial velocity dispersions and Toomre parameters of the two components. We then propose a much more accurate but still simple approximation for the effective Q parameter, which further takes into account the stabilizing effect of disc thickness. Our effective Q parameter is a natural generalization of Toomre’s Q, and as such can be used in a wide variety of contexts, e.g. for predicting star formation thresholds in galaxies or for measuring the stability level of galactic discs at low and high redshifts.

Keywords: instabilities; stars: kinematics and dynamics; ISM: kinematics and dynamics; galaxies: ISM; galaxies: kinematics and dynamics; galaxies: star formation

Journal Article.  3905 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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