In this letter we examine the role of the first supernovae in proto-galaxies , their role in feedback and the consequences for disk assembly .
Extending the picture proposed by Dekel & Silk ( 1986 ) , we argue that energetic supernovae winds can expel baryons from all proto-galaxies with varying degrees of efficiency .
The fraction of baryons retained and hence available to assemble into the baryonic disk is therefore , a function of the central velocity dispersion of the halo .
Such a coupling of the baryonic component to the dark halo leads to the following interesting consequence , a prediction for a weak scaling of the zero-point of the Tully-Fisher relation or alternatively , the mass-to-light ratio with the central velocity dispersion of the halo .
On applying to the case of the Milky Way halo , this feedback mechanism implies : ( i ) that the Milky Way halo lost \sim 10 \% of its original gas content , and the gas mass lost is roughly what is estimated for the mass in our X-ray halo consistent with the X-ray background in the soft band ; ( ii ) a range in the inferred redshift of formation z _ { f } , and the local baryon fraction f _ { b } for the Milky Way that depends on the initial spin parameter \lambda _ { h } of the halo .
In a range of viable cold-dark matter cosmological models , we find that for a low spin halo ( \lambda _ { h } \sim 0.02 ) - z _ { f } < 1 , f _ { b } \sim 2 \% ; for a median spin halo ( \lambda _ { h } \sim 0.05 ) - z _ { f } \sim 1 - 2.5 , f _ { b } \sim 5 \% ; and for a high spin halo ( \lambda _ { h } \sim 0.2 ) - z _ { f } \sim 4 - 8 , f _ { b } \sim 20 \% .
The observationally determined ages for the oldest disk stars in the Milky Way seem to rule out a low value for the spin parameter .
Given the shape of the spin distribution of halos obtained in N-body simulations , while a high value of the spin parameter is not very probable , it is interesting to note that if this is indeed the case for the Milky Way halo , then feedback processes can cause the local baryon fraction to differ significantly from the universal value .