Galactic gas fraction
= Galactic gas fraction
{title2=$f_g=M_g/(M_g+M_*)$}
This fraction compares gas <mass> with gas plus permanently locked stellar <mass> in a stated galactic reservoir. Under instantaneous recycling with a constant locking fraction and <star formation> proportional to gas <mass>, it decays as $e^{-\alpha\epsilon t}$. Gross cumulative <star formation> is not the denominator's surviving stellar <mass>.