We consider the size distribution of superbubbles in a star forming galaxy .
Previous studies have tried to explain the distribution by using adiabatic self-similar evolution of wind driven bubbles , assuming that bubbles stall when pressure equilibrium is reached .
We show , with the help of hydrodynamical numerical simulations , that this assumption is not valid .
We also include radiative cooling of shells .
In order to take into account non-thermal pressure in the ambient medium , we assume an equivalent higher temperature than implied by thermal pressure alone .
Assuming that bubbles stall when the outer shock speed becomes comparable to the ambient sound speed ( which includes non-thermal components ) , we recover the size distribution with a slope of \sim - 2.7 for typical values of ISM pressure in Milky Way , which is consistent with observations .
Our simulations also allow us to follow the evolution of size distribution in the case of different values of non-thermal pressure , and we show that the size distribution steepens with lower pressure , to slopes intermediate between only-growing and only-stalled cases .