with temperature, and the protogalactic clouds (hereafter PGC’s) are thermally unstable (Field 1965). Thermal instability leads to the rapid growth of perturbations and fragmentation of a PGC (Murray & Lin 1990). The result is that a two-phase medium develops during the initial cooling of the PGC, in which a population of warm fragmentary clouds (WFC’s) are confined by the pressure of hot, residual halo gas (RHG) (Burkert & Lin 2001). The RHG is cooled by radiative emission and conductive transport into the WFC’s (which are efficient radiators). In our earlier work, we assumed that the RHG is heated primarily by the release of the gravitational energy as the WFC’s into the central region of the halo potential, due both to their collective gravity as well as that of the dark matter. The WFC’s are unable to cool below 10$^4$ K until their density reaches a sufficiently high value that the WFC’s become self-shielded from external photo-dissociating UV radiation (Couchman & Rees 1986; Haiman, Rees, & Loeb 1997; Dong, Lin, & Murray 2003).

In the above picture, the evolution of the WFC’s is similar to that of Lyman-$\alpha$ clouds and high velocity clouds (HVC’s). Both of those systems have been proposed 