We introduce a new diagnostic for exploring the link between angular momentum and local gravitational instability in galaxy discs .
Our diagnostic incorporates the latest developments in disc instability research , is fully consistent with approximations that are widely used for measuring the stellar specific angular momentum , j _ { \star } = J _ { \star } / M _ { \star } , and is also very simple .
We show that such a disc instability diagnostic hardly correlates with j _ { \star } or M _ { \star } , and is remarkably constant across spiral galaxies of any given type ( Sa–Sd ) , stellar mass ( M _ { \star } = 10 ^ { 9.5 } \mbox { - - } 10 ^ { 11.5 } \mbox { M } _ { \odot } ) and velocity dispersion anisotropy ( \sigma _ { z \star } / \sigma _ { R \star } = 0 \mbox { - - } 1 ) .
The fact that M _ { \star } is tightly correlated with star formation rate ( \mathrm { SFR } ) , molecular gas mass ( M _ { \mathrm { mol } } ) , metallicity ( 12 + \log \mathrm { O / H } ) and other fundamental galaxy properties thus implies that nearby star-forming spirals self-regulate to a quasi-universal disc stability level .
This proves the existence of the self-regulation process postulated by several star formation models , but also raises important caveats .