Global Axisymmetric Stability Analysis for a Composite System of Two Gravitationally Coupled Scale-Free Discs

For a composite system of gravitationally coupled stellar and gaseous discs, we have carried out a linear stability analysis for axisymmetric coplanar perturbations using the two-fluid formalism. The background stellar and gaseous discs are taken to be scale-free with all physical variables varying as powers of the cylindrical radius r with compatible exponents. The unstable modes set in as neutral modes or stationary perturbation configurations with angular frequency ω = 0. The axisymmetric stable range is bounded by two marginal stability curves derived from stationary perturbation configurations. Because of the gravitational coupling between the stellar and the gaseous discs, one only needs to consider the parameter regime of the stellar disc. There exist two unstable regimes in general: a collapse regime corresponding to large-scale perturbations and a ring-fragmentation regime correspondingto short-wavelength perturbations. The composite system will collapse if it rotates too slowly and will succumb to ring-fragmentation instabilities if it rotates sufficiently fast. The overall stable range against axisymmetric perturbations is determined by a necessary D-criterion involving the effective Mach number squared Ds2 (the squared ratio of the stellar disc rotation speed to the stellar velocity dispersion up to a numerical factor). Different mass ratio δ and sound speed ratioη of the gaseous and stellar disc components will alter the overall stability. For spiral galaxies or circumnuclear discs, we further include the dynamical effect of a massive dark matter halo. Astrophysical applications to disc galaxies, proto-stellar discs and circumnuclear discs are given as examples.

作 者： Yue Shen Yu-Qing Lou   作者單位： Yue Shen(Department of Physics & Center for Astrophysics, Tsinghua University, Beijing,100084)

Yu-Qing Lou(Department of Physics & Center for Astrophysics, Tsinghua University, Beijing,100084;National Astronomical Observatories, Chinese Academy of Sciences, Beijing,100012;Department of Astronomy and Astronomy and Astrophysics, The University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 USA) 

刊 名： 天體物理學(xué)報（英文版）  ISTIC SCI 英文刊名： CHINESE JOURNAL OF ASTRONOMY AND ASTROPHYSICS  年，卷(期)： 2004 4(6)  分類號： P14  關(guān)鍵詞： hydrodynamics - ISM: general - galaxies: kinematics and dynamics - galaxies: spiral - galaxies: structure - waves  

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