Lyα Clouds from Dwarf Outflows

Abstract

We propose that cooling outflows from star-forming dwarf galaxies may account for the QSO Lyα forests, providing a explanation for both the heavy elements and large sizes recently observed for them. Supernovae shock the interstellar gas to high temperature, and the resulting gas outflows from the dwarfs owing to their shallow potential wells. The gas cools radiatively as the radiative cooling time shortens because of adiabatic expansion. Subsequent thermal instability results in condensation of clouds. The clouds inherit the kinetic energy of the flow and coast to large distances, providing regions of the absorbing gas with sizes of up to hundreds of kpc. We calculate the Lyα absorption line profiles and the neutral column distribution, and show that they are consistent with observations. We suggest that the Lyα forests are caused by the faint blue galaxies found in the deep extragalactic surveys.