Up to half of the baryons inferred to once have been in our galaxy have not
yet been detected. Ejection would seem to provide the most attractive
explanation. Previous numerical studies may have underestimated the role of
winds. I propose a solution involving a multiphase model of the protogalactic
interstellar medium and the possibility of driving a superwind. Simulations do
not yet incorporate the small-scale physics that, I argue, drives mass-loading
of the cold phase gas and enhances the porosity, thereby ensuring that winds
are driven at a rate that depends primarily on the star formation rate.
The occurrence of hypernovae, as claimed for metal-poor and possibly also for
starburst environments, and the possibility of a top-heavy primordial stellar
initial mass function are likely to have played important roles in allowing
winds to prevail in massive gas-rich starbursting protogalaxies as well as in
dwarfs. I discuss why such outflows are generically of order the rate of star
formation and may have been a common occurrence in the past.Comment: MNRAS, in press (2003): minor revisions include
