NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-06-19 T22:49:27 PDT
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For refcode 2017MNRAS.469..286R:
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Copyright by Royal Astronomical Society. 2017MNRAS.469..286R What drives gravitational instability in nearby star-forming spirals? The impact of CO and H I velocity dispersions Romeo, Alessandro B.; Mogotsi, Keoikantse Moses Abstract. The velocity dispersion of cold interstellar gas, sigma, is one of the quantities that most radically affect the onset of gravitational instabilities in galaxy discs, and the quantity that is most drastically approximated in stability analyses. Here we analyse the stability of a large sample of nearby star-forming spirals treating molecular gas, atomic gas and stars as three distinct components, and using radial profiles of sigma_CO_ and sigma_{H I}_ derived from HERA CO-Line Extragalactic Survey (HERACLES) and The H I Nearby Galaxy Survey (THINGS) observations. We show that the radial variations of sigma_CO_ and sigma_{H I}_ have a weak effect on the local stability level of galaxy discs, which remains remarkably flat and well above unity, but is low enough to ensure (marginal) instability against non-axisymmetric perturbations and gas dissipation. More importantly, the radial variation of sigma_CO_ has a strong impact on the size of the regions over which gravitational instabilities develop, and results in a characteristic instability scale that is one order of magnitude larger than the Toomre length of molecular gas. Disc instabilities are driven, in fact, by the self-gravity of stars at kiloparsec scales. This is true across the entire optical disc of every galaxy in the sample, with a few exceptions. In the linear phase of the disc-instability process, stars and molecular gas are strongly coupled, and it is such a coupling that ultimately triggers local gravitational collapse/fragmentation in the molecular gas. Key words: instabilities, stars: kinematics and dynamics, ISM: kinematics and dynamics, galaxies: ISM, galaxies: kinematics and dynamics, galaxies: star formation
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