Regulation of star formation by large-scale gravitoturbulence
Résumé
A simple model for star formation based on supernova (SN) feedback and gravitational heating via the collapse of perturbations in gravitationally unstable discs reproduces the Schmidt-Kennicutt relation between the star formation rate (SFR) per unit area, ΣSFR, and the gas surface density, Σg, remarkably well. The gas velocity dispersion, σg, is derived self-consistently in conjunction with ΣSFR and is found to match the observations. Gravitational instability triggers 'gravitoturbulence' at the scale of the least stable perturbation mode, boosting σg at $\Sigma _{g}rsim \, \Sigma _{g}^\textrm {thr}=50\, {\rm M}_\odot \, {\rm pc}^{-2}$, and contributing to the pressure needed to carry the disc weight vertically. ΣSFR is reduced to the observed level at $\Sigma _{g}rsim \, \Sigma _{g}^\textrm {thr}$, whereas at lower surface densities, SN feedback is the prevailing energy source. Our proposed star formation recipes require efficiencies of the order of 1 per cent, and the Toomre parameter, Q, for the joint gaseous and stellar disc is predicted to be close to the critical value for marginal stability for $\Sigma _{g}\lesssim \, \Sigma _{g}^\textrm {thr}$, spreading to lower values and larger gas velocity dispersion at higher Σg.
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