SIMBAD references

We investigate the stability of nearby disc galaxies and galaxies at redshift (z) equal to 4.5. We explore the connection between the stability parameter (Q_RW), star formation rate (SFR), gas fraction (f^Gas), and the time-scale for growth of gravitational instabilities (τ). We find that, despite differences in morphology 91 per cent of the nearby galaxies have a minimum value of stability parameter ($Q^{Min}_{RW}$) greater than 1 indicating stability against the growth of axisymmetric instabilities. The spirals in our sample have higher median star formation rate, lower median Q_RW, a lower f^Gas and small time scale for growth of gravitational instabilities than irregular galaxies. We find that the gravitational instabilities in spirals convert a large fraction of gas into stars quickly, depleting the gas reservoirs. On the other hand, star formation occurs more gradually over longer time-scales in irregulars with a higher gas fraction. We then compare the stability of the nearby galaxies with galaxies at $z\, =\, 4.5$. We find that net stability levels in the nearby galaxies and the galaxies at $z\, =\, 4.5$ are primarily driven by the stellar disc suggesting the presence of an inherent mechanism that self-regulates the stability. Finally, upon removing the contribution of the dark matter to the total potential, the median Q_RW for the nearby galaxies and galaxies at $z \, = \, 4.5$ remains unchanged indicating that the baryons can self-regulate the stability levels, at least in a statistical sense.