Abstract:
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 (QRW), 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 (QMin
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 QRW, 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 QRW 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.
