LYA FORESTS AND COOLING OUTFLOW FROM DWARF GALAXIES

We propose that cooling outflows from star-forming dwarf galaxies that are spatially correlated with but unbound to bright galaxies may acco unt for the QSO Ly alpha forests, thus providing an explanation for bo th the recently detected heavy elements in them and the large sizes as sociated with them. Thus, we suggest that structure formations in the early universe on scales where matter collapses gravitationally and th e gas forms stars are responsible for the Ly alpha forests (cf. the mi nihalo model). Supernovae shock the interstellar gas to high temperatu re, and the resulting gas outflows from the dwarfs owing to their shal low potential wells. The gas cools radiatively as the radiative coolin g time shortens because of adiabatic expansion. Subsequent thermal ins tability results in condensation of clouds. The clouds inherit the kin etic energy of the flow and coast to large distances, providing region s of the absorbing gas with sizes of up to hundreds of kiloparsecs. We calculate the Ly alpha absorption-line profiles and the neutral colum n distribution and show that they are consistent with observations. We suggest that the Ly alpha forests are caused by the faint blue galaxi es found in the deep extragalactic surveys.